A9L foxbody tune help

[toomanytoys]

I have a 88LX and need some help tracking down a problem. First off I have owned this car since Feb 91 and have done 99% of the work myself. The car started life as a fully loaded speed density with a auto.I have done some major work over the years and the mod list is:

stock block 331 stroker with a o-ringed block and ARP studs (balanced)
TFS Twisted wedge heads ported and polished with 1.72 roller rockers and Comp springs
Holley Systemax II intake with 75mm tb
E303 cam
Vortech S trim @ 14psi
Aeromotive a1000 fuel system and 55lb injectors
Pro-M maf with A9L conversion and MSD ignition
1 3/4 long tubes into full 3" exhaust with x pipe
manual trans conversion with a TKO 600 and Ram clutch and flywheel

When the car is cold it runs awesome however once warmed up it starts to break up when loaded (anything more than 1/3 throttle) and idles funny. If I shut the car off and try to restart, the car will not start unless I floor the gas pedal and then I get a huge black cloud when it finally starts. If I shut her down and let her sit for about 20 min everything goes back to normal until it warms up again.

I tried a new coil and cap and rotor but there was no change. The car does have a chip burned for the 55lb injectors so thats not it

Any ideas where to look or what to check? Distibutor maybe? New MSD? Engine harness?

Thanks for looking :beer:

 

[01yellercobra]

Everything you're saying sounds like a fuel issue to me. Having to hold the gas pedal down and then getting the black cloud means fuel is getting dumped when you crank it.

As for it running better when cold that could be because it's in open loop. As soon as it goes into closed loop it acts up. That could be a bad oxygen sensor or 2. A bad MAF could also cause issues.

Was the car tuned for the whole set up or is it a generic tune for the injectors?

 

[toomanytoys]

The tune was done for the whole setup. The car was fine for a while afterwards then this started. I'm not getting a cel but I'm not going by that as I think it's broken somehow. It only comes on when I first start the car

Is there any way to use a more modern computer and harness?

 

[toomanytoys]

Anyone else have any ideas?

 

[watman02]

Air leak? Did you check fuel pressure? Fuel filter pluged?

 

[toomanytoys]

Fuel pressure is good and steady. I was thinking vacuum leak and I changed the hoses, but wouldnt that happen when the car was cold as well? Is there a way to isolate the sensors to tell if there is a bad one?

 

[90redcoupe]

You need to start from the basics, If you have a wideband you need to check the AFRs when the car is warm. When the car is cold its in closed loop and might have more fuel in it. Also you need to check the TPS and make sure its around .90-.98 max. This could be part of the startup issue when its warm. Also with aftermarket injectors if the startup fuel/ECT is off or not scaled properly per the injectors you have that will cause the startup issue. I'm not sure of the chip you have either and if the settings are correct for your setup. Let me know if you have anymore questions. Also set your fuel pressure to 39-40psi vacuum off, or the chip might have a printout that list what the fuel pressure was set to when it was tuned.

 

[Don 95Vert]

Here are a couple thoughts:
If it has a switch chip with a cable, try removing the cable. It'll default to setting zero - if it is an SCT chip. The cables sometimes cause RF interference.
Ditch the MSD crap and put in stock OEM ignition components. Seen MSDs do this all the time on the dyno - OEM - never.
See above with regrds to the TFI module - when they go bad, they usually work OK when cool - and cause issues when hot.
Check 02 sensor wires, on an older Fox, the wires often lose insulation from being exposed to weather and all the heat/cool cycles - often there are tiny breaks that can cause havoc.
I have seen a couple Fox bodies with odd issues have a bad PCM - no way to test this other than throwing a new part at it.
Hope this helps.

Don

 

[toomanytoys]

I changed the TPS and set it to .92 volt KOEO and there was no change. The chip was burned at LaRoccas and it is mounted to the ecm. Not a switch chip and no cable. Tried cleaning and resetting with no change. My O2 harness is new as the old one crumbled from age (doesnt mean anything though, I know). The only MSD part I have is a 6AL everything else is OEM. Fuel pressure is 40 psi with vacuum off. I have a wideband that Im going to install as soon as possible and get some readings (although with the amount of black exhaust coming from this car I think I know what that outcome will be) . Im also gonna swap in a new TFI module and see what happens.

One more thing, I dont know if this has anything to do with it but the car doesnt have a "cold idle". The car can be sitting for a month, and as soon as I start it it drops to a warm idle (800 rpm ) immediately and is driveable.

 

[90redcoupe]

Let me know how the TFI goes sometimes that can cause ur symptoms for sure. When I tuned A9L I usually use moates quarterhorse. I like to tune the 02's off and run the car in open loop all the time but u must have a wideband installed to make corrections. This way theres no bullshit with the stock 02's trying to correct all the time.

 

[90redcoupe]

One other thing is you can try is changing the plugs or even reading them. But if u think the car is too rich and its been sometime the plugs might be pooched or even the plug wires are broken. Always try simple things first to minimize headaches.

 

[gmcconn1]

I would unplug the O2 sensors and see what happens. If it has a known good tune - runs good when cold (open loop) and poor when warm (closed loop) I would guess something with O2 sensors. Unplugging the O2s would confirm.

I would definitely dump the MSD and the replacing the TFI is good. I have been stranded more than once with a bad TFI.

 

[toomanytoys]

The wires are pretty new (Taylor 409s) and the O2 sensors are pretty new as well. I had to change them when I put the long tubes in the car as the old ones wouldnt come out. Had the car out again and noticed that the car doesnt pull this nonsense as soon as it goes into open loop. It seems to depend more on underhood temps and not engine temps. I had the hood open for 15 min after driving and the problem was gone when I restarted (came back in about 5 min).

Maybe my ECM is crapped out?

 

[90redcoupe]

Do me a favour since I dont know how that chip is setup if you a spare A9L swap it out for yours start the car drive it around but do not get into boost cause the tune will be off but I just want to factor out that the chip might be off.

 

[90redcoupe]

What have u changed on the car since the chip was originally burned for your combo??

 

[Robs87coupe]

Hey iam having the exact same problem did you figure it out?thanks!!

 

[toomanytoys]

Yes I did. I gave up on it for the winter and started back up this spring. I found 3 things:
1. There was a broken clamp on my discharge tube. It looked good from the front but was broken in the back. And it was stuck to the coupler so it looked ok
2. The reluctor wheel inside my distributor was worn and was hitting the sensor
3. Even though my plugs were fairly new at least 2 were bad

After repairing these 3 the car is back to her old self

 

[Robs87coupe]

Thanks man!!