My 86 starts fine when it's cold, but when it warms up after driving for a while it sometimes will not restart. It will usually restart a few minutes later or it may take up to an hour for it to restart. I was able to duplicate the problem in my driveway did a few tests. Fuel pressure is good, I am getting spark, and the timing is correct. There is a slight bit of oil residue in the distributor cap, and I am betting this could be helping the problem. The ICM has recently been replaced about 6 months ago with a cheapie duralast unit, so it would be wise to have that tested. I have brand new injectors from FIC. Plugs and wires are also new. What is interesting is I can clamp off the vacuum line going to the FPR and there seems to be no change at idle or when revving. I have been told to unplug the MAF while the car is running or when the problem occurs to see if that changes anything, but I have yet to try that. Any thoughts?

 

Only codes stored are 32 (because I have no EGR) and 42 (set when I checked the timing). Reset the ECM and no codes are present.

 

Coolant temp sensors are good for doing strange things like this...

Pulling the vac off the fuel reg doesn't do anything...just adds a few lbs fuel pressure. Pulling the MAF plug doesn't do anything either...except shock the ECM and $300 MAF sensor....avoid doing that. All you want to do is force it into open loop operation...do that by d/c the maf then start the car. Don't pull the plug with it running. Thats stuff about shifting into "diagnostic mode" by shocking the system is crap and spread by people that are not there to pay for your parts that get damaged by jolts in energy. There is "open loop"..."closed loop"..and "limp home mode" which is just the cal-pak program taking over. The shift to closed loop is managed by the O2 sensor...so thats a possible suspect as well.

As usual, inspect and clean all system grounds. NOT the battery ground cable...the harness grounds. On the block by the oil filter.

Do the same for the power leads on the jumper post behind the battery. Bad contacts transmit bad data....computers are only as good as the data they receive...and these cars operate on delicate electrical resistance that you can distort with dust or rust on a connection.

If fuel pressure is good and stable at around 40 psi....and inj are new, take the dist apart and clean and get a DELCO ICM and seat it in a puddle of silicone grease. THAT step is critical. Do not worry about the grease going everywhere...it will. Does not matter. It MUST transfer heat away from the ICM to the dist body for disapation.

I've never had a store brand ICM perform well. The calibration is not the same as the delco quality.

 

Check for fuel in the vacuum line that attaches to the FPR. You could have a leaky FPR diaphragm.

 

That's what I thought would happen and is why I haven't tried it yet. The 02 sensor is new as well. Cliff, I checked for fuel in the vacuum line and there is none present, although it does smell like fuel.

 

I was able to duplicate the problem again tonight and I discovered that the fuel pump is not working when this problem occurs. Turn the key to the on position, and I can't hear the pump and the car of course does not start. This only happens when the car gets warm, it never has a problem starting cold. I need to check the pump and the relay, what else should I check?

 

If you crank long enough the oil pressure switch will bypass the fuel pump relay and turn on the fuel pump. As I recall, it only takes 4 PSI of oil pressure to kick in, so it shouldn't take more than 10 seconds.

Are you sure the fuel pump in not running for 2 seconds at key on? I can't hear the fuel pump in my car if the radio or AC is on. The fuel pump priming timer is built in to the ECM and NOT controlled by the code in the EPROM. It will happen each time you turn on the key unless you didn't wait long enough after turning OFF the key. The ECM does a MAF burnoff and other stuff before it shuts down internally, which takes around 10 seconds or so.

After that first 2 second fuel rail prime, the ECM will turn on the fuel pump when it sees reference pulses from the distributor, which will happen when the engine starts cranking. The purpose of this is to keep the fuel pump off if you turn on the ignition but don't start the car.

You can force the fuel pump to come on by applying 12 volts to terminal G of the ALDL connector. The cigarette lighter is nearby and fused. On my car it's hot all the time.

 

You were right Cliff, I didn't wait long enough after turning it off. Did this again today, fuel pressure was good, it was getting spark, and it is getting power to injectors. A few minutes later it started right up and ran with no problems.

 

did we find the problem?

 

No it's still sitting in the corner of the garage for not behaving...

 

Does anyone have any more ideas?

 

I'm having a similar problem with my '89, thought I had it licked but the problem came back the following year. Check out this thread I found in the forum that might help. This will be my next step.
http://forums.corvetteforum.com/c4-t...art-issue.html

 

Betcha it's that parts store ICM.

 

I just replaced the ICM with an Accel unit...
Myfunz my car cranks fine but it just won't start.

 

Sound like it might be a bad catalytic converter?

 

Sounds like your cold start injector works.

seems like a fuel delivery problem but sounds more like a distributor related issue is causing it. Check for injector pulses @ the injector(s)/harness next time it wont "start". Checking for injector pulses may require you to crank the engine for ~ 8 - 10 seconds at a time. Also while your cranking, does the RPM gauge register anything while cranking the engine?

 

myfunz, I have no cats. engle, I connected a volt meter to the inside of the injector connector and it was getting voltage. However, I don't feel that was very accurate as I don't know what kind of voltage I should be getting. I was getting some power there though. The rpm guage does register.

 

When the ignition is on with the engine not running you will see 12 volts on one injector connector contact and zero volts on the other. You should measure the voltage on both sides as there are two injector fuses, one for each side. The pins with zero volts are all connected together and go to the ECM (light blue and light green wires).