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Discussion Starter · #1 · (Edited)
Here's a basic summary of what's going on. If you want to follow the entire scenario from the beginning, here's the original thread: http://www.moddedmustangs.com/forums/99-04/209802-car-wont-stall-idles-very-strange-please-help.html

Summary: Auto to 5-Spd swapped car, with a questionable mechanic: about 2 years after the swap I am having some shifting and idling issues where the RPM remain around 2000. This was after an attempt at cleaning the IAC to fix an ongoing stalling issue when braking. Replaced vacuum lines and a replaced IAC, took the car to a parts shop to have codes run, some of them are likely not cleared and no longer relevant, but these are the codes I got:

RELEVANT CODES:
P0708 Transmission range sensor high condition
P0743 TCC circuit condition
P0755 Shift solenoid 2 circuit condition
P0750 Shift solenoid 1 circuit condition

POSSIBLE IRRELEVANT CODES:
P1504 Idle Air Control (IAC) circuit fault
P1507 Idle Air Control (IAC) underspeed error

I have a couple immediate questions when I see these. First, how would I be having shift solenoid codes if its a 5-spd now? Could this mean that the mechanic never put a 5-spd computer in? But if that's the case, how would I have been able to run this car without any similar problems for the past 2 years? Or is it that these codes are coming back because the sensors haven't been removed and the wiring from the auto trans is still the same? But if the problem is just sensors trying to find parts that aren't there, what in the hell is causing the idle issue?

In a perfect world, I will just need to find a new ECM from a manual trans and swap them out, and my car will run as smooth as ever. Any ideas or thoughts? This one is killing me since the car is my daily driver and no longer functions at a drivable level.

I'm going to check the codes again with the mechanic that lives next door (not the same one that did the conversion) and see if any of those codes go away. Fingers crossed!
 

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King Trashmouth
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Your idling and shifting problems are likely due to a bad IAC or wiring.

The trans codes are irrelevant, as the engine can't do anything about them. You control the transmission, not the computer, so it's essentially dead ended and just throwing a code. I don't think the auto stangs have a failsafe that put the car into a limp mode if trans problems are detected.

But I would say your mechanic did not put a 5-spd computer in it. You got hosed. You're better off just getting it reflashed, since if you get a new ECM it would have to be reflashed to disable the PATS to let it work in your car.
 

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Discussion Starter · #3 ·
I can't imagine the IAC is bad still, I literally put a brand new one in this morning. I guess the wiring could be faulty though.

And about the ECM: how much would reflashing it typically run? The wife is already talking about putting the car on blocks and removing insurance because of the costs (even though I'm still under $100, she just hates the car :(). And forgive the ignorance but PATS?
 

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King Trashmouth
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I can't imagine the IAC is bad still, I literally put a brand new one in this morning. I guess the wiring could be faulty though.

And about the ECM: how much would reflashing it typically run? The wife is already talking about putting the car on blocks and removing insurance because of the costs (even though I'm still under $100, she just hates the car :(). And forgive the ignorance but PATS?
For the IAC a good voltmeter might answer your question. The circuit fault code might mean that it's shorting to ground or power, so it would be in the 0-0.5V or 4.5-5V range. Don't quote me on this, but that's how a lot of sensors/circuits work. They have an operating range that isn't from 0-5V, so that you can tell if it has shorted. You might need to do some research on that code. At the very least inspect the wiring.

Not sure how much a reflash would cost. You'll either have to deal with a dealer or tuner. The dealer is probably going to screw you royally.

PATS- Passive Anti Theft System. If you so much as replace your gauge cluster, the car won't start. It's a big pain. Thus if you swap ECM's, you'll need all the other components to "agree" with that ECM S/N, or disable it entirely with a tune.

I'd focus on resolving the IAC issues, that should take care of your problem.

Nice paint job on the car btw.
 

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Discussion Starter · #5 ·
Thanks for the info. I'll check the wiring and see if I can figure out what's going on. Hopefully, its something simple.

And thanks about the paint, its as old as the car and is not garage kept! I think I'm lucky on that one.
 

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Discussion Starter · #6 ·
So I tested the TPS since the parts store insists its that causing the problem. It showed a normal range with the multimeter and had nothing unusual going on with it so that more or less rules out the TPS as an issue. Though the parts guy still insists its hanging up on me or something.

Tomorrow I'm having the codes run again and see what comes up, then trying to exchange the IAC, I'm wondering if the new one on there isn't defective. Otherwise I may end up replacing the TPS anyhow just to see if it helps. I'm stumped on this :confused:

To make sure I'm not testing the TPS wrong, the operating range for the 5v is between 0.5-1.0 at idle, and 4.5-5.0 at wide open throttle? The return was at 5v when disconnected. I followed the Haynes, so I think I did it right!
 

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King Trashmouth
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Yeah I'd agree with the parts store on this one.
The IAC itself may be fine, but you might want to trace the wires back through the harness.

If all that checkes out OK I'm at a loss.
The primary causes of idle issues are vacuum leak, IAC, and MAF. If all those check out fine that's rather strange.

I see you did mention you had some vacuum lines replaced, I'd check to see they're routed correctly and not leaking.

The odd thing is vacuum leaks typically cause a stalling condition versus high RPM's at idle. But that would also point me toward unmetered air entering downstream of the throttle body, or even elsewhere.
 

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Discussion Starter · #8 ·
All of the vacuum lines that were replaced were checked for leaks and had clamps applied to most of the connections. Its all routed right and proper, and the mechanic next door to me checked the other lines behind the motor that weren't replaced. Those all checked out fine. We traced the wires and they all appear fine, unless there is something I'm missing inside the harness that isn't right, but from what I did initially by just cleaning the IAC I don't really see how any damage could've been caused. He tried to diagnose it but like most of the people I've talked to they are more familiar with carbureted motors.

When I went back up to the parts store the only codes that came back were those transmission codes, nothing about the TPS or IAC or anything of that nature. I'll be calling up the shop tomorrow that originally had done the transmission conversion for me to see if they can figure out this anomaly. The guy at the store also suggested calling the local auto tech schools to see if I can land a free full diagnostic.

As much as I hate to, I may just have to bite the bullet on this one and pay someone to fix it :sorry
 

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King Trashmouth
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At the very least I think your next step is seeing if you can get a reflash to a manual tune.

Maybe your mechanic thought he reflashed it to a manual and actually botched the idle tables in the process?

Beyond that it's pretty puzzling. Intuitively I wouldn't think that the transmission would affect the idle. I don't believe that auto's are like AMT's, where it's a closed feedback loop. I think the transmission purely receives commands from the ECM, and the engine doesn't change based on transmission output.
 

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Discussion Starter · #10 ·
Everyone I have talked to so far agrees that the transmission shoudn't affect anything anymore and that its only throwing codes because those sensors are still there, but the parts are not. It's just hitting a dead end when the signal tries to fix things.

As for the reflash, that may be what the mechanic suggests when I take it in or talk to him. I'm just hesitant to take it to someone if its only the EGR or TPS or something simple because I'm going to pay twice as much.

Nice Cobra build by the way. I like the idea of building it ground up, who cares if you could buy a real one for the same price you invest? Haters gonna hate. I personally want to build a 2v Cobra Killer once I finish school.
 

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King Trashmouth
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Everyone I have talked to so far agrees that the transmission shoudn't affect anything anymore and that its only throwing codes because those sensors are still there, but the parts are not. It's just hitting a dead end when the signal tries to fix things.

As for the reflash, that may be what the mechanic suggests when I take it in or talk to him. I'm just hesitant to take it to someone if its only the EGR or TPS or something simple because I'm going to pay twice as much.

Nice Cobra build by the way. I like the idea of building it ground up, who cares if you could buy a real one for the same price you invest? Haters gonna hate. I personally want to build a 2v Cobra Killer once I finish school.
Hmm. The EGR and TPS are usually pretty good about throwing codes when they go bad. Worth a look though. Have you adjusted the throttle stop screw any?

And I advise against the 2v idea, 2v's just do not flow as well as 4v's. Looking back I say make yourself a nice unassuming looking 4v TT. Those things will eat Supras alive all day long. Even single turbo's are formidable. There's a guy back home with a 97 Cobra vert, single 76mm turbo, putting down close to 800rwhp. That thing is downright frightening.
 

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Discussion Starter · #12 ·
Come Monday I'm going to the junk yard to find a MAF, MAP, EGR, and TPS to replace mine and see if any of that helps. I just don't have the money to buy all of those new and end up not fixing it. I'm also trying to track down the mechanic that did the original swap today, but he moved shops and has a new number and it's proving difficult.

As for the 2v vs 4v, I still like thinking about a 2v with all the work done by me putting down big numbers, but I know the 4v has more potential. I'm only aiming for 400-450 rwhp, so I don't need the full potential of a 4v for what I want. I'd like it to still be my daily! By the time I'm done with school and actually have the $$$ for it my mind may have changed. I'm even thinking about finding a decent '85 Fox to work on so I don't have to worry about the FI and associated ECM problems I'm having to deal with now!
 

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Discussion Starter · #13 ·
I'm headed to the junkyard for parts in question (MAF, MAP, TPS and EGR) and was told that the Grand Marquis uses the same motor and parts are interchangable. I also know several other fords that use the 4.6L modular motor (Crown Vic, F-150) and was wondering if those would be compatible.

Is it true that I can use those parts from a Grand Marquis, Crown Vic or F-150?
 

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Discussion Starter · #15 · (Edited)
JKQ have an exchange policy if the part doesn't work. So if my car get worse when I put it on, then yeah, its junk. Haha! And I have heard recently that the MAF may not work because it has application specific programming, unless I have a reprogrammer (tuner, I'm guessing?) which I don't.

And about that Interceptor motor, what year is it that you have in the car? Are you planning on getting rid of it at any point in time? I'm wondering if its any better than the PI motor in mine.
 

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King Trashmouth
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Yeah, I think MAF's have individual calibrations. I could be wrong though.

And funny you mention about the interceptor. Not sure what year it is, PO said it had 40k on it. It's certainly clean and runs strong.
And here's the fun part; I will be ditching it as soon as I get my car down here and swap the cammed termi motor in. I'm going to try and sell it as a complete liftout, all accessories, clutch, trans, everything you'd need.

As to it's benefits, I can't directly attest. I've heard lots of rumors about it over the years, nothing I could confirm. Everything from a higher flowing water and oil pump, bigger injectors, heavier duty bearings, to a more agressive ECM tune. Not sure about any of these, but there must be a reason they have no problem running these motors to 300k mi.
 

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Discussion Starter · #17 ·
Do you have numbers from the block? I could try and find out. I'm just curious about it. You're sure about that mileage? And what kinda price are you looking at for all that stuff? Transmission info? I was planning on rebuilding my motor once I finish school and have that knowledge, but if a new setup came that offered more potential I'd definitely be open to it. I'm going to start looking more into it.

But not to forget about what this thread started I'll post results to the part hunt and swap. I may ask a buddy if I can swap his parts out to see if those do the trick.
 

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King Trashmouth
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Right now the car is still in storage back in NY. I'm waiting for all the salt and crap to be off the roads before I move it, which of course could be awhile in Buffalo. I'll have to look up the serial numbers when I pull it.

To be honest, I'm not sure how much more potential it would give you, but it's sure a clean motor that runs great. I can't directly verify the milage on it, but the chassis has 55k on it, and came with the original motor that had popped a head gasket seperate, with the P71 installed.

Behind the engine is an aluminum flywheel and Centerforce II clutch, with an 01 Cobra T3650 transmission. I only state the difference with the Cobra because the Cobra and Mach's had a different top gear ratio due to their 3.55:1 rear ends. If anything it would help if you went to a higher gear ratio. I may or may not keep the flywheel and clutch for my new setup, I haven't decided yet.

Bottom line is it's a great setup that runs strong. The only reason I'm swapping it out is to go to a termi drivetrain, which is quite an upgrade. I'll have to do some research before I throw out a price.

But more importantly, good luck with your swap.
 

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Discussion Starter · #19 ·
SOLVED!

I checked all the wiring and made sure the harnesses were connected properly, there was a wiring issue on BOTH the IAC and TPS, secured the wiring and reset the computer. A half hour of driving later the car is running nearly 100%. The only exception is the idle is still a bit high when slowing down, around 1100-1400RPM, but I think the computer may still be resetting its parameters.

I'm thrilled! Thanks for all the help!
 
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