North American Turbocoupe Organization



'88 Rough Idle, Stall, Usual Stuff Checked
oneowner88lx Offline
Member
#1
I am working on an '88 Mustang that I swapped an '88 TC engine/ecu/VAM/sensors into. The car has a slightly rough and inconsistent idle, varies about 50 to 100 rpm intermittently. If the car is warm and I rev it up high (4000+ rpm) it will stumble for a minute or so then smooth out. Sometimes it will stall after reving. But it always revs crisp and fast. I have heard HLAs will do that but engine did not do it when it was in the donor car (bad frame). When everything was in the TC it idled so smooth you didn't even know the engine was running. But unfortuately TC was not savable due to frame damage. The Mustang seems to drive fine out on the road, pulls up hills easily, boost comes on smoothly, but it will stall if reved up and then clutch is pushed in within a short time after reving. If driven moderately it never stalls just has the rough inconsistent idle that was not there when engine was in the other car. Car starts easily all the time. Car does not smoke or run hot.

The KOEO and KOER tests come back with 81,82,83 which is the IRCM missing and should not cause problems.

Did boost leak check to 17 PSI on the in car guage, replaced throttle shaft seals, vacuum hoses, etc so it is leak free. VAM to turbo hose does not leak. All new felpro intake gaskets.

Replaced TFI, PIP, new Motorcraft wires, two sets of Motorcraft plugs, new cap/rotor, and it did not fix the problem.

All three temp sensors (VAT, ECT, ACT) have the correct resistence back at ECU connector in both hot and cold conditions.

All grounds zero ohms back to battery: pin 20, 40, and pin 60. Valve cover to negative battery zero ohms. Valve cover to shock tower bolt zero ohms. All engine compartment connectors (sensors, actuators, injectors) have been verified to be zero ohms back to their respective pins at the ECU connector. Full battery voltage (13.8 at idle) at distributor, coil, IAC, and EGR vent solonoid. VAM voltage is about .82 and looks steady. Headlights are nice and bright. Turbo housing grounded to Pin 49. O2 has good ground and full battery power. VREF is 5.2 volts at VAM and TPS.

Adjusted base idle to 750, TPS voltage set to .95. Base timing at 10 and with spout in it jumps to 25, looks stable, and increases when reved.

IAC is new (no change, old one worked fine on TC), throttle body clean, EGR is blocked off for now because it had a small air leak.

New 255 LPH fuel pump and pick up filter, new Wix fuel filter, new Kirban adjustable fuel pressure regulator. Pressure set at 39 vacuum hose off at idle, 30 with hose on, rises during boost, and goes back down once out of boost.

I tried unplugging the BAP sensor; no change, unplugging O2 sensor, no change, unplugging IAC and turning idle up, no change.

All plugs the same color, compression 140 PSI exactly on all cylinders, throttle body was held open and injectors unplugged during test.

With a timing light I sometimes see spark misses and replacing all the ignition components has not changed that. I see the misses when on the coil wire two but they are intermittent maybe one every 3-5 seconds or so. I can tough all ignition wires and never get shocked. No arcing visible when run at night.

If I pull the spout I do not see misses on the timing ligh. But turning distributor to increase timing with spout out does not smooth it out.

Here is a video that shows the problem. The idle is not smooth to begin with then after the moderate rev it gets really bad then smoother out over time. We have not seen the idle get really bad like that with just a moderate rev before or since but that is how it behaves with a high rev with engine warmed up:

http://www.youtube.com/watch?v=4cQ6uvsX-Rk

In this one you can see the air fuel ratio is in a pretty good range but not stable. The scope shows the TFI controlling the coil with the spout plugged in:

http://www.youtube.com/watch?v=i6s3ULxsBHw

Any advice greatly appreciated, thanks,
Bill

'88 Turbo Coupe
'88 Mustang LX 5.0L 5 spd Conv (one owner survivor)
'88 Mustang Hatchback 2.3 turbo 5 spd
'86 SVO ultra low mile survivor
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oneowner88lx Offline
Member
#2
Also, the exhaust manifold is ported and the upper intake is gutted and lower knifed. The car was an automatic and converted to a 5 speed.
Bill

'88 Turbo Coupe
'88 Mustang LX 5.0L 5 spd Conv (one owner survivor)
'88 Mustang Hatchback 2.3 turbo 5 spd
'86 SVO ultra low mile survivor
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tr_guy79 Offline
Senior Member
#3
Wow... Seems like you covered about everything...

Did you test the full sweep of the TPS for breaks? As far as the missing, I have never seen a 2.3T that didnt have an intermittent miss at idle to some degree.

Did you double check your TPS voltage, AFTER setting your base idle?
3rd Annual Philly Tri-State NATO Meet - http://natomessageboard.com/ultimatebb.p...p=1#000003

'87 - Range Roller 4* adv / 50 trim t04e / Ported E6 / Gutted Knifed intake / Stinger 3->2.5" / Adj. Cam Pulley / Warlboro 255

To Do: PIMP/MS2, FMIC, Bigger Inj
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Pete D Offline
Administrator
#4
Yeah Sure looks like you covered the bases. How about checking out the VAM. Is it mounted in a funny position? Have you checked it out or tried substitution?
Pete Dunham


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oneowner88lx Offline
Member
#5
Thanks for the suggestions.

Both TPS and VAM have a smooth sweep with no spikes. TPS is .95 volts with engine running and I did checked after base timing was set. VAM voltage looks like a steady .82 volts at idle. I am going to check VAM voltage at the ECU harness although wires are zero ohms between VAM and ECU connector.

I'll keep looking and update on what I find.
Bill

'88 Turbo Coupe
'88 Mustang LX 5.0L 5 spd Conv (one owner survivor)
'88 Mustang Hatchback 2.3 turbo 5 spd
'86 SVO ultra low mile survivor
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oneowner88lx Offline
Member
#6
I tried uplugging spout, turning timing up to 35, and it ran the same.

But here is something interesting: with timing fixed at 35, IAC unplugged, and my son holding VAM door open to get .82 volts it idles smooth and consistent. NOTE: with IAC plugged in VAM voltage is .82 and steady. When IAC is unplugged RPMs drop and VAM voltage drops to .45 or so. We did not adjust idle speed screw when we took the video.
Here is the video:

http://www.youtube.com/watch?v=YHSd6DXXIc8

We measured TPS voltage at .99 today.

So as you can see the engine has the ability to idle smooth and consistent and the ECU does a good job firing injectors.

We were seeing timing light misses when the car was running smooth with spout out and IAC unplugged so it must be timing light because it was running smooth as you can see in the video.

With IAC plugged in and moving VAM door with finger we can't get the engine to smooth out.

Here it is with IAC unplugged, ECU controlling timing (25 degrees), and my son holding VAM door to keep it at .82 volts:

http://www.youtube.com/watch?v=3ZY_F7z9yXw

Pretty smooth but if you look closely you see a little bit of shake in vacuum needle. But overall pretty good idle just not as good when timing is fixed.
Bill

'88 Turbo Coupe
'88 Mustang LX 5.0L 5 spd Conv (one owner survivor)
'88 Mustang Hatchback 2.3 turbo 5 spd
'86 SVO ultra low mile survivor
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tr_guy79 Offline
Senior Member
#7
Is the car up to operating temperature in the O2/TFI video? On the EEC-IV you should see a continuous rich/lean bounce when the ECM is in closed loop (though I am not sure if the system you are using is quick enough to pick up on it. If it is warmed up, and still in open loop, that points to a problem somewhere

This is just a thought (typed brainstorm)

With the spout out, the ECM has no control over spark, and with the IAC unplugged it has no control over air. The only variable left for the ECM to control, is the amount of fuel going into the engine. Opening the VAM door "tells" the ECM that there is more air entering the intake tract, which should cause the ECM to add more fuel. So if adding more fuel smooths out the idle, then I would say I am leaning towards a possible dirty/clogged injector. This could cause the symptoms you are having with the idle, but I am not so sure it would cause the stall problem or bouncing vac. Opening the VAM may add enough fuel to compensate for the clogged injector, but without adding enough fuel that it starts choking out the other cylinders. I dont have the info in front of me of how to, but I would reccomend running the ECMs internal balance test. I have never had one come back bad, but It might be worth a shot. I have also found pulling one plug or injector connection at a time helpful. If you pull one and the idle is consistent (thought still rough) you have found your offending cylinder. At that point it could still be a number of things, but at least you know where to look.


Are their ANY other driveability issues?

Hope some of this made sense... Maybe it will at least make a "lightbulb" moment for you or someone esle...

-Shane
3rd Annual Philly Tri-State NATO Meet - http://natomessageboard.com/ultimatebb.p...p=1#000003

'87 - Range Roller 4* adv / 50 trim t04e / Ported E6 / Gutted Knifed intake / Stinger 3->2.5" / Adj. Cam Pulley / Warlboro 255

To Do: PIMP/MS2, FMIC, Bigger Inj
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oneowner88lx Offline
Member
#8
Thanks for suggestions.

All the spark plugs are the same color so I don't think its an injector:

[Image: plugs3.th.jpg]

The 2.3 is not sequential fuel injection so you can't do a balance test, the LA3 ECU does not support it. The 2.3T fires two injectors at a time so the ECU can't do a balance test. Only engines like the 5.0L HO which are SEFI support the balance test.

The car was fully warmed up during the videos.

Thanks again for your suggestions.
Bill

'88 Turbo Coupe
'88 Mustang LX 5.0L 5 spd Conv (one owner survivor)
'88 Mustang Hatchback 2.3 turbo 5 spd
'86 SVO ultra low mile survivor
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tr_guy79 Offline
Senior Member
#9
It will do a balance test on an '87... Cant say that it is useful, but I have done it on my '87 just to see what happened, and it passed.

I am pretty much stumped otherwise, and as long as I have been messing with 2.3T Fords, that's a tough thing to do...

I am VERY curious to hear what this turns out to be. I am thinking it still is related somewhow to your A/F acting like the ECM is in open loop.

Did you check VAT?

-Shane
3rd Annual Philly Tri-State NATO Meet - http://natomessageboard.com/ultimatebb.p...p=1#000003

'87 - Range Roller 4* adv / 50 trim t04e / Ported E6 / Gutted Knifed intake / Stinger 3->2.5" / Adj. Cam Pulley / Warlboro 255

To Do: PIMP/MS2, FMIC, Bigger Inj
Reply

oneowner88lx Offline
Member
#10
The VAT, ACT, and ECT were checked at the ECU connector in both cold and warm conditions and all three sensors have the correct resistence both hot and cold.

The VAM has .25 ohms closed and 4.55 ohms open and no dead spots in between.

I hear you about it being lean but why does the LM1 wide band hover right around 14.7 with IAC hooked up and spout in and idle is rough?

Yes it is a tricky one but I'll keep plugging away.
Bill

'88 Turbo Coupe
'88 Mustang LX 5.0L 5 spd Conv (one owner survivor)
'88 Mustang Hatchback 2.3 turbo 5 spd
'86 SVO ultra low mile survivor
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