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87 Mustang GT
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Discussion Starter · #1 ·
I used to be on a Mustang forum years ago but took some time off with doing much of anything to our GT. With a supportive wife and a son at home, they've got me interested back again into Mustangs.
My youngest son and I installed a new camshaft with major help of one of my friends at work with.
The camshaft is a Lunati 51014. Also, we installed new lifters and pushrods.
After some time, everything went together well.
We also did a base idle reset after everything was complete and adjuster the TPS. The idle has been a nightmare. I'll get it set then after i drive it again the idle issue starts.
It will idle around 700 for 30 seconds then drop to 500 for another 20 seconds then up to1000 for another 30 then back to 700. I have changer Idle air control too.
Under hard pull it runs really strong for what it is. The problem is at low-speeds ,30-35 in 5th gear, it jerks and bucks.
Any ideas would be helpful.
 

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2014 GT, 1967 Fairlane GTA
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The 1987-88 speed density fuel injection doesn't respond well to any changes to the engine. Unless you put an MAF conversion on it then I doubt that you'll be able to get a proper running car with an aftermarket cam in it. My guess is that the ECM is hunting for a good idle speed but can't find it due to sensors detecting things out of parameters and it can't adjust for it because the speed density system is less adaptable to change than an MAF system is.
Btw, I'd love to see a pic of your car. I love t-tops fox bodies.
 

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If the TPS sensor is really old it might be giving erratic readings to the pcm. When mine failed on my old Mark vii it would sporadically hold the throttle open at a rpm even when taking my foot off the the pedal while driving.
 

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87 Mustang GT
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Discussion Starter · #5 ·
I used to be on a Mustang forum years ago but took some time off with doing much of anything to our GT. With a supportive wife and a son at home, they've got me interested back again into Mustangs.
My youngest son and I installed a new camshaft with major help of one of my friends at work with.
The camshaft is a Lunati 51014. Also, we installed new lifters and pushrods.
After some time, everything went together well.
We also did a base idle reset after everything was complete and adjuster the TPS. The idle has been a nightmare. I'll get it set then after i drive it again the idle issue starts.
It will idle around 700 for 30 seconds then drop to 500 for another 20 seconds then up to1000 for another 30 then back to 700. I have changer Idle air control too.
Under hard pull it runs really strong for what it is. The problem is at low-speeds ,30-35 in 5th gear, it jerks and bucks.
I just realized I forgot a change to our Mustang.
it has been converted to mass air. The mass air meter is 73 mm and it’s calibrated to the 24 lb. Injectors too.
Any ideas would be helpful.
The 1987-88 speed density fuel injection doesn't respond well to any changes to the engine. Unless you put an MAF conversion on it then I doubt that you'll be able to get a proper running car with an aftermarket cam in it. My guess is that the ECM is hunting for a good idle speed but can't find it due to sensors detecting things out of parameters and it can't adjust for it because the speed density system is less adaptable to change than an MAF system is.
Btw, I'd love to see a pic of your car. I love t-tops fox bodies.
I appreciate the response because it let me know I forgot to add a piece of information
It’s been converted to mass air with a 73 mm mass air. And it has 24 lb injectors.

If the TPS sensor is really old it might be giving erratic readings to the pcm. When mine failed on my old Mark vii it would sporadically hold the throttle open at a rpm even when taking my foot off the the pedal while driving.
Thanks for your response.
The TPS is fairly old so I’ll give that a try.if I has to guess id say 10-15 years. Maybe more.
 

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What is your rear gear? I have 3.73s and with my custom cam i cannot run 1400 rpm in 5th at a really low load; which is like 35 mph. It bucks. Just the nature of the beast. Not sure the camshaft specs for your car, but anything radically different than stock with stock rear gears probably wont mesh that well




Just did more research, this is the current offering from lunati with those cam specs

Street/Strip Hydraulic Roller Cam - Ford 351W & 302 H.O. 284/292 (lunatipower.com)

3.55 rear gear required or better.

I appreciate the response because it let me know I forgot to add a piece of information
It’s been converted to mass air with a 73 mm mass air. And it has 24 lb injectors.
Just to add a few more things.

Im assuming you went with a "calibrated MAF"? These are ok, but are kind of a band aid. You might not ever get a really nice running car at idle with a calibrated maf, new injectors, and a cam change.

As far as i understand these calibrated MAFs, all they do is scale their MAF curve. You're tricking the ECU into thinking there is less air flowing into the engine than there is. So the computer is relying on the stock tune to run the car which is programmed for injectors with different flow characteristics and a stock cam.
 
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87 Mustang GT
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Discussion Starter · #7 · (Edited by Moderator)
What is your rear gear? I have 3.73s and with my custom cam i cannot run 1400 rpm in 5th at a really low load; which is like 35 mph. It bucks. Just the nature of the beast. Not sure the camshaft specs for your car, but anything radically different than stock with stock rear gears probably wont mesh that well.

Just did more research, this is the current offering from lunati with those cam specs

Street/Strip Hydraulic Roller Cam - Ford 351W & 302 H.O. 284/292 (lunatipower.com)

3.55 rear gear required or better.
It has 373 gears

Just to add a few more things.

Im assuming you went with a "calibrated MAF"? These are ok, but are kind of a band aid. You might not ever get a really nice running car at idle with a calibrated maf, new injectors, and a cam change.

As far as i understand these calibrated MAFs, all they do is scale their MAF curve. You're tricking the ECU into thinking there is less air flowing into the engine than there is. So the computer is relying on the stock tune to run the car which is programmed for injectors with different flow characteristics and a stock cam.
I bought the mass air kit from Fiveology racing.
it came with everything to convert to mass air.
 

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Looked at their site, did you buy the kit with the maf for 24lb injectors? Other than that cant give you a really definitive answer without seeing some sort of data log. Does the car smell rich?

Sorry for not being anymore help
 

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I had a surging idle after upgrading a few things. I did a base idle reset with no improvement. Then figured out I missed a couple steps.

When you did yours, did you unplug the spout connector on the distributor and the IAC before setting initial idle around 600 rpm (I missed the spout connector first time). Then followed the rest of base idle reset instructions. Later I still had some minor surging and disassembled and cleaned my IAC REALLY GOOD. Disconnected the solenoid part and cleaned the plunger area as good as possible with brake cleaner. I blew it out, reassembled and reset the computer. Much better now. Here is cold start afterward...


Video was intended to show AFR's on start up, but shows idle just as well.

My combo in the video is a stock bottom end 302, GT40 3-bar heads with 1.7RR, Crower 15512 cam, Explorer upper and lower intakes with 70mm TB and EGR and 24 lb injectors. Exhaust is MAC equal length shortie headers and a full 2.5" catted exhaust. I have a 76mm C&L MAF with a calibration tube of my own sizing, so yes I am tricking the computer, but it works. No other tuning, just the stock A9P (auto) computer.

Not sure what brand your MAF is, but if it is a C&L 73 and they gave you the blue calibration tube, I think that may be why you are a little rich.
 

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87 Mustang GT
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Discussion Starter · #11 ·
I had a surging idle after upgrading a few things. I did a base idle reset with no improvement. Then figured out I missed a couple steps.

When you did yours, did you unplug the spout connector on the distributor and the IAC before setting initial idle around 600 rpm (I missed the spout connector first time). Then followed the rest of base idle reset instructions. Later I still had some minor surging and disassembled and cleaned my IAC REALLY GOOD. Disconnected the solenoid part and cleaned the plunger area as good as possible with brake cleaner. I blew it out, reassembled and reset the computer. Much better now. Here is cold start afterward...


Video was intended to show AFR's on start up, but shows idle just as well.

My combo in the video is a stock bottom end 302, GT40 3-bar heads with 1.7RR, Crower 15512 cam, Explorer upper and lower intakes with 70mm TB and EGR and 24 lb injectors. Exhaust is MAC equal length shortie headers and a full 2.5" catted exhaust. I have a 76mm C&L MAF with a calibration tube of my own sizing, so yes I am tricking the computer, but it works. No other tuning, just the stock A9P (auto) computer.

Not sure what brand your MAF is, but if it is a C&L 73 and they gave you the blue calibration tube, I think that may be why you are a little rich.
Thanks for responding to my test.
I did unplug the spout when idle base idle reset.
also I installed a news idle air control valve. I ordered a news TPS to see if that would help. I’ll post after I get it installed.
As for mass air meter I had a by fiveology racing installed. Its actually a 75 mm not 73.
 

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The problem is at low-speeds ,30-35 in 5th gear, it jerks and bucks.
I have 3.73s and with my custom cam i cannot run 1400 rpm in 5th at a really low load; which is like 35 mph. It bucks. Just the nature of the beast.
Doing the math, if you are running a stock height tire (25.8") and a stock T5 (overdrive being 0.68) along with the 3.73 gears - 30 mph will be 985 rpm, 35 mph will be 1150 rpm. The solution ... at those speeds keep it in 4th. Those rpms will always lug engine and jerk and buck - in any gear.
 
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