87 Mustang 5 speed running really rich hard start when warm....

Topic: 87 Mustang 5 speed running really rich hard start when warm.... (Read 8881 times) previous topic - next topic

87 Mustang 5 speed running really rich hard start when warm....

December 03, 2013, 06:02:37 PM

Hey kiddies!

It's been awhile. Not much to report on my end. Looking for someone to repaint a few panels on the Cougar that the last guy screwed up and refuses to make good on (deadbeat). Wish I had the patience and facilities to do body work myself.....

I digress.

Got one for you that honestly has me stumped...
This is a buddies car that he recently acquired. It's an '87 Mustang Gt with t Tops and a 5-speed, still running speed density with a DA1 ECU. The car has stock everything save for exhaust and gears and sat for about 3 years before he got it. Needless to say it needed a little TLC to get it going.

As it sits right now it runs horrendously rich at all times. The car also is quite hard to start after warm. Cold startup is flawless. On warm/hot starup she turns over as if it has a severely low battery that sat in an Alaskan winter overnight.

Battery is new, distributor and TFI module are known good. Fuel pressure regulator is stock. Fuel pressure is good and within parameters. When the problem was first described to me I thought about the HEGO harness and the possibility of it not being hooked up correctly. My buddy chased the wires last night and it is in fact hooked up correctly. Interestingly enough, disconnecting the HEGO harness from the engine harness shows no change in how it runs. Due to the richness, the car does not want to idle lower then 850 RPM and even at that RPM it's quite choppy. It smooths out if it is bumped to 1000.

I should add that the o2 sensors are new as well. Battery voltage is good and alternator is charging like a champ. There are no extra electrical components added to the car. Still has the stock speakers and head unit.

I'm thinking it's either a wiring problem somewhere in the HEGO harness or a faulty ECU. Am I on the right track here?

87 Mustang 5 speed running really rich hard start when warm....

Reply #1 – December 03, 2013, 06:20:46 PM

Your thoughts are possible. I'd check the fpr for leaks. Pull the vac hose off of it and see if your smell fuel.

87 Mustang 5 speed running really rich hard start when warm....

Reply #2 – December 03, 2013, 06:41:15 PM

87 t top kinda rare

Pull any codes ?

87 Mustang 5 speed running really rich hard start when warm....

Reply #3 – December 03, 2013, 06:44:02 PM

I'd look for corrosion in/on the ground wires. They can loose conductivity over time. Replace the battery ground wire and check the EEC ground. I've cleaned the connection before (thinking that was enough) and actually had a bad cable. Once I split it open it was filled with corrosion. That corrosion caused a resistance and led to problems.

87 Mustang 5 speed running really rich hard start when warm....

Reply #4 – December 03, 2013, 06:48:58 PM

One other thing to check would be the computer's temp sensor. (Not the one for the gauge.) The computer might be thinking the car is cold all the time and adding fuel, not getting out of warm-up logic. That might explain why the O2 sensor made no difference.

87 Mustang 5 speed running really rich hard start when warm....

Reply #5 – December 03, 2013, 07:18:07 PM

That could be it

87 Mustang 5 speed running really rich hard start when warm....

Reply #6 – December 03, 2013, 07:48:10 PM

FPR is good. No smells. It's getting a good vacuum signal. All grounds have been replaced. The guy who picked this car up has been pretty thorough due to how long it sat. No codes other than canister purge solenoid which is out of the car (it was bad). I've seen these cars run without those before without issue.

Quote from: flylear45;425207

One other thing to check would be the computer's temp sensor. (Not the one for the gauge.) The computer might be thinking the car is cold all the time and adding fuel, not getting out of warm-up logic. That might explain why the O2 sensor made no difference.

I'll let him know on that. Didn't even come to mind to me when I was giving the car a once over.

I'll keep you guys posted

87 Mustang 5 speed running really rich hard start when warm....

Reply #7 – December 03, 2013, 10:12:37 PM

i'd start with checking all the sensors, mainly the coolant temp sensor, intake air temp sensor, and map sensor

87 Mustang 5 speed running really rich hard start when warm....

Reply #8 – December 03, 2013, 10:20:17 PM

It is a possibility even without a code. The computer throws a code when a sensor is out of range. If it fails to read properly but is in range.....no code. I just fixed an issue similar to this on my son's 89 Daytona. Modern cars are a bit smarter, but they still lie, too.

87 Mustang 5 speed running really rich hard start when warm....

Reply #9 – December 04, 2013, 04:42:36 AM

Paul, Check the TPS for broken wires.

87 Mustang 5 speed running really rich hard start when warm....

Reply #10 – December 04, 2013, 04:57:15 AM

X2 on TPS or wiring. I had a coolant temp sensor go "bad" and cause symptoms like you describe, as well. That was on a 5.0 F series truck. Later on, the FPR went bad, and it also caused the same problem. Would run like a raped ape till the engine got warm, then acted like it was getting loads of fuel dumped in (because it was, technically).

If all that pans out, I'd also check the O2's and their connections/wiring.

87 Mustang 5 speed running really rich hard start when warm....

Reply #11 – December 04, 2013, 05:34:36 AM

Clogged cat?

87 Mustang 5 speed running really rich hard start when warm....

Reply #12 – December 04, 2013, 06:02:43 AM

check the timing. maybe someone swapped a cam in and set it too far advanced or retarded, or dropped the dist in wrong. could be firing all the injectors to the wrong cylinders.

87 Mustang 5 speed running really rich hard start when warm....

Reply #13 – December 04, 2013, 06:40:06 AM

Quote from: 88turbo;425221

Paul, Check the TPS for broken wires.

That WOULD throw a code.

87 Mustang 5 speed running really rich hard start when warm....

Reply #14 – December 04, 2013, 07:06:35 AM

Quote from: Dougy_Fresh;425213

i'd start with checking all the sensors, mainly the coolant temp sensor, intake air temp sensor, and map sensor

Yes, and the vacuum hoses, too. The map line is known to crack.

He did cap off the line to the manifold when he removed the charcoal cannister?