Can you diagnose this engine problem ?????

1990 Vette starts instantly on first crank, runs good, idles good, for the first few minutes, sometimes longer, then quits. Can not get it to start again.

Leave it set for awhile will start instantly on first crank, run a short while then die.

Before it dies, it runs good, then very, very light roughness, then quits suddenly.

During periods when it dies and will not start, I can prime the intake with either and it will run.


What I have done so far:

First of all, the only codes that I get from the ECM is a code 12.

Looks like fuel flow problem: but not .

Fuel pump and intake strainer has less than 3000 miles.

Fuel pump is running, 40 some pounds of pressure in the fuel rail. Checked both before starting and after engine dies.

Changed fuel filter, checked for water, no help.

Let car set for a couple of hours, starts on first crank, idles good, put in gear, drove 100 feet, dies and will not start. Will run on either.

The only codes that I get from the ECM is a code 12.

Any suggestions ????????

 

Okay, you know that you have fuel.....

Next run the car until it dies. Then check for spark. The problem sounds like it is related to heat. Like something once it is heated then cuts off voltage (assuming no spark to the plugs).

 

It does run on either, so it has spark.

 

Based on your post.....car quits and does not start again until it sits for a couple of hours.

So if you hit it with starting fluid it will start....does it continue to run? OR does it run for a few minutes and then dies again? You have attached the fuel pressure gauge and watch the gauge as the car runs and then dies and it has a constant 40 psi. If you leave the gauge on over night what does it read in the morning? Faulty gauge?

Any smoke out the rear end as it states to run rough and then dies? Check spark plug to see if you are running too rich? You might be flooding out. But when you hit it with starting fluid there is enough spark to push it into starting??? A smell of raw fuel?

 

If you have a noid light handy,plug into an injector plug to see if you are loosing injector pulse. Possibly a faulty driver in the ecm without throwing a code.

 

Ignition Coil or Ignition Control Module, all in the distributor cap. These two in particular are more likely to fail once heated.

 

I agree, I was going to say Fuel Injectors when you said it starts with Ether, but if your getting a steady supply of fuel, I say Coil or ICM. Both of these can be affected by heat, but so can the Injectors....WW

 

Both of these items are super cheap and easy to swap out. If you haven't done it in awhile, replace the distributor cap and rotor while you are in there. My Coil was way out of spec on resistance and my ICM was suspect as I too had problems once heated up. Your local auto parts store can usually check the ICM for you (special diag tool) for free but they would be only checking it cold, that is unless you can get it off quick and have oven mitts.

 

I agree. This is the first thing I do on a no start to rule out a spark issue at least for the time being. If the car temporarily starts at will using starter fluid I just confirmed spark is there and I don't have to waste my time looking at the spark side for nothing. I can focus on fuel. If it still does not start with starter fluid I attach my inductive timing light to any plug wire and see if the timing light flashes while cranking. If it does there is spark going though that wire. Because it starts with ether I would not pursue a spark issue at this point. Obviously there is spark or it would not have started with ether or starter fluid at all. Based on this I would focus on fuel right now not spark. Your tests thus far have not completely verified fuel delivery all the way down into the cylinders.

I would verify injector pulse now. You have correct pressure at the rail but are the injectors being commanded (pulsed) to spray and are they physically able to spray fuel into the cylinder if and when they are pulsed? Since we know that when you spray ether in the intake the engine starts we know spark is there because it started. So we need to know if fuel is actually physically being sprayed into the cylinders or not.

Get a noid light kit. You can rent them at Autozone or buy one at Harbor Freight. Plug a noid light into an injector connector and crank it again during the no-start time (the same time when ether is able to start the engine but it won't start on it's own). Test both banks (sides) of the engine with the noid light.

The noid light should flash on/off at each injector plug on each bank while you crank. Each injector has two wires. One is voltage with the key on and the other is the ground wire. The ECM switches the ground wires on/off to spray the injectors while voltage remains constant on the voltage wire. On the L98 the ECM has one common ground wire for one bank and another for the other bank of 4 injectors. Each bank of 4 injectors also share a common voltage wire on each side on an L98.

No flashing noid light means no injector pulse for whatever reason (either no voltage feed or no ecm pulsed grounds) and injectors are not being commanded to spray. On an L98 the distributor sends a signal to the ecm that the engine is rotating. If this signal is not there it will not pulse the injectors to ground.

Good injector pulse does not mean the injectors are firing. It means they are being told to fire. Ohm each injector individually with an ohm meter. The spec for L98 is 16 ohms plus/minus a couple ohms. Ohm testing will tell you if there is a break/open in the coil or too much resistance. But it cannot tell you for sure if the injector is actually spraying fuel into the cylinder or anything about the actual spray pattern.

A way to know for sure if a injector can spray fuel without removing it is by attaching your fuel pressure guage to the rail. Cycle the key a few times and leave it in the key on/engine off position to fully pressurize the rail. Fuel pressure should be steady at this point. If you supply one terminal of the injector with ground and the other with voltage you should see a sharp and instant drop in fuel pressure on your guage the instant you do so. This proves that injector pintle actually physically opened and sprayed pressurized fuel into that cylinder when commanded manually. No drop in fuel pressure on the guage when you energize the injector directly means it did not physically spray any fuel into that cylinder.

If you can verify fuel delivery all the way down to the cylinders during the no-start and the problem is still there check the timing and check spark strength.

A healthy coil should be able to jump a 30kv gap using an adjustable spark tester like this. This one is made by Thexton.

 

I like that tester! Where and how much?

 

Amazon $11. One of the best tools you can buy.

 

Wow! good analytical mind, there. I'm storing this for the day my turn comes!

gracias,
joe

 

Just ordered one of those. Thanks for the tip!

 

I have 2002 ZO6 started car column steering lock light comes on and I tried to put in gear it dies. Pull battery it's an optimin 75/35 charge is good any ideas.will pull codes and post

 

And then post them in the C5 section. My work here is done, now back to NASCAR, Thunder in the valley... Oh, go Jimmie

 

Check for injector pulse. You may have failing injector(s). If the injectors resistance gets too low, it will knock out the ECM's injector driver.

Ohm test your injectors.
Watch Jon's video on ohm testing.

http://forums.corvetteforum.com/c4-t...questions.html

 

Im with this guy, but leaning towards the ICM first.....

 

My issue was if it wasn't started for a couple of days it wouldn't start. So I would spray starter fluid in and it would start up. I replaced the filter, fuel pump, injectors and was better for awhile then it started to do the same thing. Next I replaced the ICM, coil, rotor, cap and it was doing great, until a couple of weeks ago when I took my sweetheart out for ice cream and what seemed to be in front of the whole world my car just cranked. Went walking for some starter fluid put it in and it started right up. Now I have to wait until it is in the non start mode to check for something else.