88 Mustang Smog Pump bypass - Ford Mustang Forum
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post #1 of 13 (permalink) Old 10-17-2019 Thread Starter
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88 Mustang Smog Pump bypass

I have an 88 5.0 and the smog pump locked up on it. I had a 84.5 inch belt that I put on several years ago and bypassed the smog pump. After I put it on the car started running very poorly. It was backfiring, very little power etc. I put the original belt back on and the car ran fine for the last several years. The smog pump locked up and left me stranded me a few days ago. I put the 84.5 inch belt on again and bypassed the smog pump. Now the car is running poorly again. I only saw 2 vacuum lines going to the pump I removed both of them and capped them off. Everything that I have read says the smog pump should not cause any problems if it is taken off. What could be the problem? It is stock with speed density computer.

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post #2 of 13 (permalink) Old 10-18-2019
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That is an odd one.The only time a thermactor system component should cause an issue is when the system is in place and functioning,but a component is defective.Otherwise it should not affect how the car runs at all.All the smog pump does is send fresh air to the heads during the first couple minutes of runtime then to the lower cats after that,to help the cats create the catalytic reaction thats needed in order for them to function.Open the link at the bottom then scroll down to post #10 & read a very detailed description of how the thermactor system and its components work.
Make sure youve got the correct vacuum lines connected to the egr valve and the evr solenoid,which is the solenoid on the upper/rear side of the passenger strut tower.One line should run from a rear intake vacuum port to the lower vacuum port on the evr solenoid then one line should run from the upper evr solenoid port to the egr valve.Those vacuum lines and the lines to the thermactor valves get crossed sometimes and cause an issue.
You can run code tests using a jumper wire and a 12v test light connected to the appropriate terminals at the diagnostic port on the rear side of the driver strut tower area.The 86-88 models dont have a functional check engine light,so thats what the 12v test light is for.The 2nd link at the bottom will show you where to connect the jumper wire and test light and how to run the tests.The light will flash the codes out.Youll likely have codes for the thermactor system,but see if codes are present for any other system or component also.
If your smog pump and the other thermactor components were functioning and your cats had been removed and you were having backfiring issues,I could see how the smog pump sending air to either the heads or the hpipe might create a lean condition, without the cats being there to consume/ use up that air,but once the smog pump is put out of commission,by deleting it or bypassing it,theres no air traveling thru any of the components to cause a lean condition.However,you could try disconnecting the hose on the diverter valve,that runs between the valve and the crossover pipe (that runs to the back of both heads) then cap/plug the crossover pipe and do the same to the now open port on the diverter valve.Maybe one of the valves or hoses is leaking and drawing in outside air (basically creating a vacuum leak) thats upsetting the afr.Here is another important factor.If you're still running cats,the smog pump and every other thermactor system component must be kept in working order because the cats depend on the air from the smog pump being present and if its not,the cats will clog and fail in short order.So if your cats are still in place,better get a smog pump back on it quick.If cats are present without a functional smog pump,that could be whats causing the backfiring.I should have mentioned this right off the bat,but I guess I assumed your cats had been removed already.They could be starting to clog and thats the reason why it runs normally when the smog pump is connected,but abnormally once you bypass the smog pump.




https://www.stangnet.com/mustang-for...-to-it.477938/


DIY KOEO/KOER/Cylinder Balance Self-Test Procedure

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post #3 of 13 (permalink) Old 10-19-2019 Thread Starter
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That is an odd one.The only time a thermactor system component should cause an issue is when the system is in place and functioning,but a component is defective.Otherwise it should not affect how the car runs at all.All the smog pump does is send fresh air to the heads during the first couple minutes of runtime then to the lower cats after that,to help the cats create the catalytic reaction thats needed in order for them to function.Open the link at the bottom then scroll down to post #10 & read a very detailed description of how the thermactor system and its components work.
Make sure youve got the correct vacuum lines connected to the egr valve and the evr solenoid,which is the solenoid on the upper/rear side of the passenger strut tower.One line should run from a rear intake vacuum port to the lower vacuum port on the evr solenoid then one line should run from the upper evr solenoid port to the egr valve.Those vacuum lines and the lines to the thermactor valves get crossed sometimes and cause an issue.
You can run code tests using a jumper wire and a 12v test light connected to the appropriate terminals at the diagnostic port on the rear side of the driver strut tower area.The 86-88 models dont have a functional check engine light,so thats what the 12v test light is for.The 2nd link at the bottom will show you where to connect the jumper wire and test light and how to run the tests.The light will flash the codes out.Youll likely have codes for the thermactor system,but see if codes are present for any other system or component also.
If your smog pump and the other thermactor components were functioning and your cats had been removed and you were having backfiring issues,I could see how the smog pump sending air to either the heads or the hpipe might create a lean condition, without the cats being there to consume/ use up that air,but once the smog pump is put out of commission,by deleting it or bypassing it,theres no air traveling thru any of the components to cause a lean condition.However,you could try disconnecting the hose on the diverter valve,that runs between the valve and the crossover pipe (that runs to the back of both heads) then cap/plug the crossover pipe and do the same to the now open port on the diverter valve.Maybe one of the valves or hoses is leaking and drawing in outside air (basically creating a vacuum leak) thats upsetting the afr.Here is another important factor.If you're still running cats,the smog pump and every other thermactor system component must be kept in working order because the cats depend on the air from the smog pump being present and if its not,the cats will clog and fail in short order.So if your cats are still in place,better get a smog pump back on it quick.If cats are present without a functional smog pump,that could be whats causing the backfiring.I should have mentioned this right off the bat,but I guess I assumed your cats had been removed already.They could be starting to clog and thats the reason why it runs normally when the smog pump is connected,but abnormally once you bypass the smog pump.




https://www.stangnet.com/mustang-for...-to-it.477938/


DIY KOEO/KOER/Cylinder Balance Self-Test Procedure
Thanks for the information. I have an offroad xpipe so I don't have cats. I haven't checked the codes lately but for several years I have been getting code 44 or 45. I am sure which one. The car was running good so I didn't worry about it. I am going to remove the hoses and cap them off like you suggested. I was thinking I might have a check valve stuck open and letting exhaust leak into the heads. What is your opinion on that theory? It's not a daily driver so it may take a few weeks to get the problem resolved. I will keep you updated on what I find. My worst case scenario is replacing the smog pump. Thanks again for your help.
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post #4 of 13 (permalink) Old 10-21-2019
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If youve got an offroad xpipe,the smog pump and every other thermactor system component can be removed completely because those components are serving absolutely no purpose now that the converters are gone.Codes will likely be present afterwards,but those codes will not cause any driveability issues,as long as the system was deleted properly (i.e. - you plugged the vacuum hoses,capped the xpipe airtube,etc) Any codes related to the removal of those components are called "soft codes" and they harmlessly stay dormant in the ECU.Their only purpose is to help you repair the thermactor system back to original factory specs,if you were ever to add converters again and needed the thermactor system intact.

I can see how your theory of leaking check valves could be a possible cause of the backfiring,but Im not sure just how possible?? You mentioned removing the vacuum hoses from the smog pump,but I believe you meant to say (& Im assuming of course) that you removed the vacuum hoses from the tab & tad valves?? If my assumption is correct,removing those hoses would trigger the following
** When the vacuum source is removed from the bypass valve,it triggers the valve to dump any air flowing through it out of its silencer ports,which dumps the air to atmosphere. **
** When the vacuum source is removed from the diverter valve,it triggers the valve to dump any air flowing through it out of the port thats connected to the xpipe airtube hose,which dumps the air to the xpipe.**
So with that said,I wonder if outside air is being drawn into the bypass valve,via its silencer ports since they're always open now with the vacuum source removed, then making its way thru the diverter valve & on to the xpipe,where its likely creating a lean condition and subsequent backfiring??
Another possibility could be if unburned fuel is reaching the exhaust where its igniting and causing backfiring.Then once you reconnect the smog pump and its air reaches the exhaust,its leaning it just enough to compensate for the unburned fuel and this is removing any backfires.
If you remove the diverter valve hoses from the crossover pipe and the xpipe airtube,then cap both pipes and the backfiring disappears,your theory about the check valves may be spot on.

I should've asked in the first place,but this backfiring is in the exhaust,right,and not in the intake??

If code 44 popped up with the smog pump/thermactor system functioning, that code usually means the crossover pipe and/or the thermactor passage on the passenger side of the pipe or head is clogged with carbon buildup.The carbon will be so hard you'll have to use a chisel,
dremel tool,etc to clear the pipe or head passage.That condition would normally send more smog pump air to the driver side passage,causing a o2 sensor lean code on the driver side,but since your problem is only occurring when the smog pump is bypassed,a clogged pipe/head passage would have no bearing on the backfiring condition.If it was the other way around & the backfiring was occurring with the smog pump running,then a clogged pipe could be the cause.
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post #5 of 13 (permalink) Old 10-21-2019
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Is it possible that the problem lies somewhere with the 84.5” belt and not the smog pump? For example, it might not be turning this or that fast enough or possible too fast? If it was running prior to it seizing up I’d replace the pump and be done with it.

Last edited by 90lxwhite; 10-21-2019 at 10:22 PM.
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post #6 of 13 (permalink) Old 10-22-2019
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The only thing is,it would be a waste for him to buy a smog pump since he doesn't have converters anymore.

1991 Mustang lx
D.S.S. 342ci {10.5:1}
TFS 190cc + track heat
Lunati 61011 .549".565"
Pro-M 76mm maf
Jetronic 30lb inj
QA1 Coilovers
17" Weld ProStar XP's
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post #7 of 13 (permalink) Old 10-22-2019
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Quote:
Originally Posted by wbrockstar View Post
The only thing is,it would be a waste for him to buy a smog pump since he doesn't have converters anymore.
I know it. I just priced them, I was thinking that they were closer to $100 than $200, but that doesn’t seem to be the case. I guess he could try the delete pulley for $50, but that might be a gamble. If I found one cheap enough it’d be worth it to be up and running vs pulling my hair out. It won’t hurt anything having one and not needing it.

Last edited by 90lxwhite; 10-22-2019 at 10:56 PM.
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post #8 of 13 (permalink) Old 10-23-2019
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I know it. I just priced them, I was thinking that they were closer to $100 than $200, but that doesnt seem to be the case. I guess he could try the delete pulley for $50, but that might be a gamble. If I found one cheap enough itd be worth it to be up and running vs pulling my hair out. It wont hurt anything having one and not needing it.

Damn thats outrageous!!! If mine wasnt close to seizing up,I'd send him the one Ive got in my garage.I haven't ever opened one up to see what internals it has,& it probably wouldn't help anyways due to the lack of availability of those parts,but if it was possible to buy those parts,a rebuild would likely be easy and, maybe,inexpensive?? There cant be more than just a few parts that makeup the smog pump.Im also curious about what those parts are so I can try & understand why they seize up so often when they're on a car,but not being used for months or when they're pulled off the car and stored inside a garage??If they go bad when shelved,why don't they do the same when sitting on the shelf at the parts store??
I was thinking theres a leak somewhere, along the thermactor system hoses/ pipes/valves,thats not causing any problems when the smog pump is forcing air through the system,but once that air is cutoff,by bypassing the smog pump,the leaking component is then drawing outside air into the system thats causing a vacuum leak and afr issues??

1991 Mustang lx
D.S.S. 342ci {10.5:1}
TFS 190cc + track heat
Lunati 61011 .549".565"
Pro-M 76mm maf
Jetronic 30lb inj
QA1 Coilovers
17" Weld ProStar XP's
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post #9 of 13 (permalink) Old 10-24-2019 Thread Starter
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Quote:
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Is it possible that the problem lies somewhere with the 84.5 belt and not the smog pump? For example, it might not be turning this or that fast enough or possible too fast? If it was running prior to it seizing up Id replace the pump and be done with it.
I don't see how it could be the belt since I am not having charging or overheating problems. I agree with wbrockstar that I have another problem that the smog pump was covering somehow. I capped off the tube going to the xpipe and the tube going to the heads. It runs a lot better now. It still has occasional loss of power and misfires. I am going to run codes and check for vacuum leaks. I have other vehicles I can drive so I am going to try to resolve the problem but worst case scenario would be to buy a new smog pump.
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post #10 of 13 (permalink) Old 10-24-2019 Thread Starter
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If youve got an offroad xpipe,the smog pump and every other thermactor system component can be removed completely because those components are serving absolutely no purpose now that the converters are gone.Codes will likely be present afterwards,but those codes will not cause any driveability issues,as long as the system was deleted properly (i.e. - you plugged the vacuum hoses,capped the xpipe airtube,etc) Any codes related to the removal of those components are called "soft codes" and they harmlessly stay dormant in the ECU.Their only purpose is to help you repair the thermactor system back to original factory specs,if you were ever to add converters again and needed the thermactor system intact.

I can see how your theory of leaking check valves could be a possible cause of the backfiring,but Im not sure just how possible?? You mentioned removing the vacuum hoses from the smog pump,but I believe you meant to say (& Im assuming of course) that you removed the vacuum hoses from the tab & tad valves?? If my assumption is correct,removing those hoses would trigger the following
** When the vacuum source is removed from the bypass valve,it triggers the valve to dump any air flowing through it out of its silencer ports,which dumps the air to atmosphere. **
** When the vacuum source is removed from the diverter valve,it triggers the valve to dump any air flowing through it out of the port thats connected to the xpipe airtube hose,which dumps the air to the xpipe.**
So with that said,I wonder if outside air is being drawn into the bypass valve,via its silencer ports since they're always open now with the vacuum source removed, then making its way thru the diverter valve & on to the xpipe,where its likely creating a lean condition and subsequent backfiring??
Another possibility could be if unburned fuel is reaching the exhaust where its igniting and causing backfiring.Then once you reconnect the smog pump and its air reaches the exhaust,its leaning it just enough to compensate for the unburned fuel and this is removing any backfires.
If you remove the diverter valve hoses from the crossover pipe and the xpipe airtube,then cap both pipes and the backfiring disappears,your theory about the check valves may be spot on.

I should've asked in the first place,but this backfiring is in the exhaust,right,and not in the intake??

If code 44 popped up with the smog pump/thermactor system functioning, that code usually means the crossover pipe and/or the thermactor passage on the passenger side of the pipe or head is clogged with carbon buildup.The carbon will be so hard you'll have to use a chisel,
dremel tool,etc to clear the pipe or head passage.That condition would normally send more smog pump air to the driver side passage,causing a o2 sensor lean code on the driver side,but since your problem is only occurring when the smog pump is bypassed,a clogged pipe/head passage would have no bearing on the backfiring condition.If it was the other way around & the backfiring was occurring with the smog pump running,then a clogged pipe could be the cause.

Yes the backfiring is coming from the exhaust with a loss of power at the same time. The vacuum hoses that I capped off were the two that plugged into valves along the hose coming from the smog pumg to the heads and crossover tube. Is that the TAB and TAD valves? I capped off the tube going to the xpipe and the tube going to the heads. It runs a lot better now. It still has occasional loss of power and misfires. I am going to run codes and check for vacuum leaks. If the EGR is stuck open could that cause the problem? It is the original EGR so it probably isn't working correctly. What are your thoughts of removing the EGR and putting a plate over the holes? Do I need the plug that fools the computer into thinking the EGR is working properly? If I don't get a code for the EGR I will just leave it alone. I had a problem similar to this once before but with the smog pump working. I unplugged the 02 sensors and the problem went away. I later replaced the 02 sensors. Do you think it could be bad 02 sensors but didn't make the car run bad with the smog pump operational? I am going to try to resolve the problem but will just replace the smog pump if I can't.
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Yes the backfiring is coming from the exhaust with a loss of power at the same time. The vacuum hoses that I capped off were the two that plugged into valves along the hose coming from the smog pumg to the heads and crossover tube. Is that the TAB and TAD valves? I capped off the tube going to the xpipe and the tube going to the heads. It runs a lot better now. It still has occasional loss of power and misfires. I am going to run codes and check for vacuum leaks. If the EGR is stuck open could that cause the problem? It is the original EGR so it probably isn't working correctly. What are your thoughts of removing the EGR and putting a plate over the holes? Do I need the plug that fools the computer into thinking the EGR is working properly? If I don't get a code for the EGR I will just leave it alone. I had a problem similar to this once before but with the smog pump working. I unplugged the 02 sensors and the problem went away. I later replaced the 02 sensors. Do you think it could be bad 02 sensors but didn't make the car run bad with the smog pump operational? I am going to try to resolve the problem but will just replace the smog pump if I can't.

(Q) Is that the TAB and TAD valves?
(A) Yeah those are indeed the TAB/TAD valves you removed the vacuum hoses from.

(Q) If the EGR valve is stuck open could that cause the problem?It is the original EGR so it probably isn't working correctly.What are your thoughts of removing the EGR and putting plate over the holes

(A) If the EGR valve is stuck open,it will essentially create a vacuum leak,which causes a lean condition.A few things to note about the EGR system and the EGR
Eliminater plug.When the EGR valve is open,it triggers the ECU to lean the fuel mixture and advance timing.Anytime a code is set for the EGR system,it triggers the ECU to delete/bypass EGR function in the EECIV,so that the fuel and timing values will remain normal vs being altered like stated above.What the EGR Eliminater does is,it outputs a voltage equivalent (0.50) to the value of a closed EGR valve,so that the ECU will see a always closed EGR valve and run normal fuel and timing values and it also prevents the cel from coming on,if the code is one that triggers a cel.The cel would not affect you anyways since the 86-88 models didnt come with a cel.You dont need the Eliminater anyways,since the ECU shuts the EGR function off with a code present.All youve gotta do is remove the vacuum hose from the EGR valve and plug the hose.This will trigger a code,which will trigger the ECU to delete the systems function and fuel/timing values will remain normal.A free trick that can be used for someone having a cel on due to the EGR is to remove the EVP sensor from the EGR valve,push the sensor rod in until the sensor reads a value around 0.50 volts then wrap tape around the sensor and rod to hold it in that voltage position,super glue the rod then once it dries,remove the tape,bolt the sensor back on the EGR valve (unless you'd rather use a blockoff or delete plate to totally delete the EGR valve) reinstall the EGR valve (or just the plate by itself) then plug the wiring harness back in.If youve got a blockoff plate or delete plate,just leave the EVP sensor off the valve and ziptie just the sensor up out of the way somewhere.This trick keeps you from needing the Eliminater plug.If your EGR valve is leaking,just get rid of it and install a plate or you can make your own out of a piece of sheet metal.

(Q) Do you think it could be bad 02 sensors but didn't make the car run bad with the smog pump operational?

(A) Alot of time,o2 sensors will set a code (41,91,42,92) if they're defective,but these codes can also be caused by many other issues too,so dont go replacing the o2 sensors everytime a code pops up for them.Test them first.As an example, something as minor as a lean or rich condition will set those codes.A loose or disconnected hego ground wire could cause a lean o2 code also.The possibilities go on when it comes to things that can cause codes for the o2 sensors.Its very important that o2's react quickly to the changes in the exhaust, which indicates whats going on in the motor or efi system.They need to switch from lean to rich to lean,etc rapidly to keep the afr stoich.As o2 sensors age,their ability to measure o2 in the exhaust and their reaction time slows down,which is referred to as a lazy sensor so when the ECU tries to compensate for the o2 readings (by richening the system if the o2's are reading a lean condition or leaning the system if the o2's are reading a rich condition) its imperative that the o2's read correctly and quickly.If not,the changes the ECU makes will run behind somewhat because of the speed at which the o2's are operating at,if they're lazy.IOW - by the time the ECU sees a lean reading from a lazy o2,it might have already changed to a stoich or rich reading by the time the ECU has gotten around to compensating for that lean condition.The following link details how to properly test the o2's.


O2 Sensor Codes 41/42/91/92 Troubleshooting

1991 Mustang lx
D.S.S. 342ci {10.5:1}
TFS 190cc + track heat
Lunati 61011 .549".565"
Pro-M 76mm maf
Jetronic 30lb inj
QA1 Coilovers
17" Weld ProStar XP's
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post #12 of 13 (permalink) Old 10-28-2019 Thread Starter
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I got codes 44,94,42,92,13. I unplugged the O2 sensors and the car is running ok. Do I need to check O2 sensors and replace if bad? If it won't cause a problem I would just as soon leave them unplugged.
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I got codes 44,94,42,92,13. I unplugged the O2 sensors and the car is running ok. Do I need to check O2 sensors and replace if bad? If it won't cause a problem I would just as soon leave them unplugged.

The o2 sensors are not necessarily bad.Code 44/94 could be present because of the smog pump being bypassed.No smog pump air to the heads would trigger the ECU to set codes 44/94 due to lack of flow at the thermactor passages at the rear of both heads.If the smog pump is working,but flow is not present at the thermactor passages,that would indicate the crossover pipe or thermactor passages are clogged with hard carbon buildup.The ECU toggles the tab(bypass) valve on/off then looks for changes in the o2 sensor readings,as a way of testing the smog system.When the bypass valve is toggled open,the o2 readings should go up (i.e.- the o2's should indicate a lean condition) When its toggled close,the o2 readings should go back to normal.

The reason your issue is disappearing when you disconnect the o2 sensors is because you're forcing the ECU into Open Loop mode when you disconnect the o2's.In open loop,the engine runs on pre-set fuel & timing values stored in a lookup table and the majority of the efi sensors on the engine are not used during this time.If a sensor is out of range so much that the ECU cant compensate for it,the engine will normally run fine when the ECU is operating in Open Loop mode,but once it goes into Closed Loop mode,driveability issues will normally begin,if a sensor is way out of range.When the engine reaches operating temp & the o2 sensors are heated up,the ECU goes into Closed Loop mode and runs the engine using feedback from all the sensors,especially the o2 sensors.If the engine is cold,if the o2 sensors are disconnected,if the check engine light is on or if the throttle is in the WOT position,the ECU will revert back to Open Loop mode.

Code 42 and 92 indicate a rich condition. If excess or unburned fuel is making its way to the xpipe,this could be the backfiring & code 42/92 cause.A leaking injector,leaking FPR or a stuck open canister purge valve could cause a rich condition/codes.If you run a cylinder balance test,it may id a suspect injector if youve got one leaking or stuck open. Check the fpr by disconnecting its vacuum hose,start the engine,look for fuel seeping out of the regulator vacuum port or fuel in the vacuum hose.If either is present,the regulator is bad.To check the purge valve,clear the codes,remove its vacuum hose at the outlet port,plug the hose,cap the valve port and drive the car for 15 minutes then run codes again.If 42/92 gone,the purge valve is bad.

1991 Mustang lx
D.S.S. 342ci {10.5:1}
TFS 190cc + track heat
Lunati 61011 .549".565"
Pro-M 76mm maf
Jetronic 30lb inj
QA1 Coilovers
17" Weld ProStar XP's
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