Runs like a pooch! - Ford Mustang Forum
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post #1 of 9 (permalink) Old 4 Weeks Ago Thread Starter
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Runs like a pooch!

I'm having the dreaded runs good for a minute then bucks and stalls backfires when I let off the gas. Always smells like gas.....etc.... One thing I noticed is I can completely cover my throttle body opening and my engine won't die. When I set base idle, idle screw is backed all the way out iac is unplugged and new. Engine still idles. It has a professional products tb egr plate and intake. Should it still idle?

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post #2 of 9 (permalink) Old 4 Weeks Ago
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Sounds like you have a vacuume leak..... time for a smoke test or swap the professional products TB & intake out back to the oem parts....

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post #3 of 9 (permalink) Old 4 Weeks Ago
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Quote:
Originally Posted by Andy2373 View Post
I'm having the dreaded runs good for a minute then bucks and stalls backfires when I let off the gas. Always smells like gas.....etc.... One thing I noticed is I can completely cover my throttle body opening and my engine won't die. When I set base idle, idle screw is backed all the way out iac is unplugged and new. Engine still idles. It has a professional products tb egr plate and intake. Should it still idle?
Yeah man, it should still idle without the IAC plugged in. As a matter of fact, one adjusts the idle with the IAC unplugged and the motor up to operating temperature. It could be a vacuum leak, but anytime I’ve had one the poor idle was a constant. Where as what you described sounds like it’ll idle until you give it gas and let off.
Scan for error codes. You might not get any, but it’s a good place to start. If you don’t have an OBD code reader use a paper clip. Google the instructions, they’re out there.
It also could be a fuel pressure issue. You’ll need a tester to ruel that out. It’s an easy test but the tester isn’t all that cheap. I had a harbor freight one that was $40 (I think) and it only lasted a handful of tests before it crapped out.
But yeah start with error codes.
*Edit*
There are lots of things that can cause those symptoms and OBD1 is pretty vague even if it does throw a code.
This might help but you’ll need a volt/multimeter.
https://www.stangnet.com/mustang-for...cklist.698148/
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post #4 of 9 (permalink) Old 4 Weeks Ago
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Is this a SD car or MAF?? It'll still run with the air intake hose off if its SD (86-88) If its MAF,it normally wont run with the hose off.Reconnect the hose then disconnect the MAF harness and see if it will run & if it does,does it run better with the harness removed?? If yes,the MAF sensor is dirty/ defective,the wiring/plug may be suspect.

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 #5 of 9 (permalink) Old 4 Weeks Ago Thread Starter
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Sd car
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post #6 of 9 (permalink) Old 4 Weeks Ago
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Quote:
Originally Posted by Andy2373 View Post
Sd car

Ok.Check for vacuum leaks.A vacuum leak will cause the o2 sensors to read lean which will trigger the ecu to richen the fuel mixture,causing obnoxious fumes at the tailpipes & possible driveability issues.The purge valve and carbon canister hoses are known to dryrot & cause vacuum leaks and since the map sensor is probably the #1 or #2 most important sensor on a SD car,check it thoroughly.Make sure the canister purge valve isnt stuck open too,because it will cause an unmetered (rich) fuel condition. Just disconnect its vacuum hose on the intake side of the purge valve,plug the hose and see if it runs any better.Next,to make sure the egr system isnt causing your problem,remove the vacuum hose from the egr valve,plug the hose and see how it runs.If it runs better,troubleshoot the egr system.Anytime a code is present for a egr component,the ecu deletes/bypasses its operation in the ecu logic & it disables its function so that the ecu can run normal fuel and timing values,which are normally adjusted to compensate for the gases anytime the egr valve is open.However,if the egr valve is stuck open because of alot of carbon buildup or a defective evr solenoid, egr gases will still be allowed to pass into the engine and without the ecu compensating for these gases,driveability issues will likely occur.Next test,If youve got a multimeter,disconnect the harness from the ect sensor & touch a meter lead to each terminal on the ect sensor.Test it cold then warm the engine up and test it hot.The ohms value should match the chart below for the given temp listed.If the values are off,go ahead & replace the ect sensor.Reconnect the harness when testing is done.Next test,start the car up and let it run.Pull the vacuum hose off the fuel pressure regulator and see if fuel is seeping out of the regulator port or if the vacuum hose is wet with fuel.If either condition is present,replace the regulator.Next test fuel pressure.Autozone rents test kits for a refundable deposit or you can buy a gauge to permanently mount or you can use a tire pressure gauge,but it may not be 100% accurate.The Schrader valve (test port) is located on the stainless fuel line section a few inches from where the line connects to the fuel rail near the passenger valve cover.Pressure should be:
Key on/engine off= 35-45psi
Key on/engine running= 30-40psi

It also wouldn't hurt to pull KOEO/KOER codes.If you dont have a scanner,use a jumper wire/paperclip and a test light,since the 86-88 models dont have a check engine light.The diagnostic port is at the driver strut tower/firewall.The following link will help.The second white diagram you come to at the site in the following link shows you where to connect the jumper wire and test light.The test light will flash the codes out for you.The test directions and code list is also there.For each code set you get (if any) each set of codes will be flashed twice (OD & CM) If codes arent present,you should get code 11 (system passed code) Post any codes you get.Do the cylinder balance test afterwards.It will help you id any suspect injectors.
If none of the tests above fail,leaking, buldging or eroded posts on any/all of the 3 blue capacitors on the ecu circuit board and/or a damaged trace on the board can also cause your symptoms,but do these checks after all other tests have been completed,since the ecu is a small pain in the to remove from behind the passenger kick panel.

Good luck


EEC-IV
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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

Last edited by wbrockstar; 4 Weeks Ago at 11:58 AM.
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post #7 of 9 (permalink) Old 4 Weeks Ago
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BTW- I dont think it would cause your current issues because the iac is used for idle,but if you develop any idle issues,cut the diode out thats spliced into your iac harness wires,if youve got a new/remanufactured iac with the diode built-in.The diode is pictured below.Once you remove it,splice the red wires back together then cover them and the white/lt blue wire with heat shrink.This diode will compete with the iac valve diode and idle issues will begin.Some experience this problem and some dont.The following link explains the tsb.

1983 Ford Bronco TSBs & FSAs (Recalls) for '83-96 Broncos & F150s picture | SuperMotors.net
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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 #8 of 9 (permalink) Old 4 Days Ago Thread Starter
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Is it to good to be true? I did the harness diode delete, and I feel like something was lifted off of me! I tried everything. All new parts, smoke test! No vacuum leaks by the way. My car runs like it's supposed to.this forum has been the best source for info. Thank you
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post #9 of 9 (permalink) Old 4 Days Ago Thread Starter
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Wbrockstar you are the master! Lol
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