Help! Very strange starting

[EEvette]

Hello everyone,

I am what i like to call strange starting issues. I am by no means an expert but this problem is driving me nuts.
First a few things ive done to try and solve the problem.
1) New Fuel pump/filter
2) New IAC valve
3) New exhaust system (no restriction issues)

Ok so this is what happens, I first turn the switch to start the car and it cranks for maybe four or five seconds and then starts. I have noticed that if I turn the switch and let go right away, at the second try it starts like a champ.

Please help like im sure everyone here has, Ive invested quite some money on this car.....its all worth it when it runs though!

 

[JimBobC4]

I think you have a fuel pressure leak down issue.

Check pressure at the schrader valve on the fuel rail.

 

[EEvette]

Thanks Jim

I will do so.....I also forgot to mention that once it starts it idles perfectly.

Oh, and I have a wet kit nitrous system on it...I have not used it yet, but the test port is connected to the fuel soleniod on the kit. I doubt this has anything to do with it but mind as well make mention of it.

 

[TedC]

EEvette, Disconnect the injectors and measure resistance and report back. They should all be very close to each other (in the 16 ohm range). Also, is your ECM EPROM the stock EPROM or was it customized? In 1989 GM added a longer delayed start to increase the crank time, improving starting oil pressure. 1989 EPROM code is a popular base to customize from because of the higher timing advanced curves vs. prior years and the elimination of the 9th injector used for cold start.

 

[EEvette]

TedC,

I have an 86, as far as the ECM I personally have not modified/upgraded it. This is a recent issue so it is safe to say it is not due to an ECM upgrade. I will check the injectors' resistance as soon as I get home from work.

I just passed emissions inspection last sunday so I know the engine is not running too rich.

I will post the injector readings later this afternoon.

 

[EEvette]

Ok, I read the resistance on all 8 injectors yesterday. They all read between 16.1 and 16.2 ohms.

 

[TedC]

That is good news on the injector front. Just one bad injector (low resistance) can cause the ECM not to pulse any of the injectors. Would suggest investing in the factory service manuals. Some other suggestions... When you turn the key to run (do not start the engine) do you hear a click (fuel pump relay). I would check then make sure you are getting fuel pressure on the rail and that this pressure holds. Pull a plug wire and check for a spark during this condition. Check timing.

 

[EEvette]

I have also checked the fuel pump and the relay. I can hear the pump activate as soon as I turn the key....might be the timing.

I will look into getting the factory service manuals since I have the Haynes but thats not quite as good I hear.

Thanks for all your help and I will report back if I find the problem.

 

[Ezmunie]

Keep us posted on what you figure out as I'm having the same problem

 

[EEvette]

Would a bad or about to go bad ICM cause this problem?

 

[TWISTERUP]

Would a bad or about to go bad ICM cause this problem?

Doesn't sound like the ICM to me

I think you have a fuel pressure leak down issue.

Check pressure at the schrader valve on the fuel rail.

I agree with JimBobC4--Have you checked fuel pressure at the rail yet ?
I know you've ohmed the injectors..the resistance may check OK and they could still be leaking down (not holding pressure) over time. The time lapse you feel when cranking may be the time it takes the fuel pump to build pressure back up in the fuel lines/ fuel rail and the injectors

 

[muddywaters]

That's exactly what my 88 was doing. Injectors ohms were ok. Fuel system would not hold pressure. Replaced the injectors with Bosch GenIII's and my problem was solved. Starts hot/cold, runs beautiful. I'm sure there could be other issues, but the fuel pump was changed, could be the regulator. More than likely it's the injectors leaking down and I thank all who got back to me with the solution.

 

[EEvette]

I will check fuel pressure next....how long would I need to leave the gauge in place before I can determine if there is/isnt loss in pressure?

 

[TedC]

You have verified injector resistance. This means that the ECM should be able to pulse the injectors properly. It is important to verify that the rail is getting pressure, and the right pressure. Injector leak down is usually a problem on a hot soaked engine. I guess it could occur on a cold engine. My 1988 had leaking injectors, and it still started like a champ when cold. Did you check for spark during cranking? This is an easy test, and can help it determining if we should be looking for an ignition issue. When you measure fuel pressure, measure first in run (do not start) and record what happens at the start and after 5 minutes. Then start the engine and measure again. Record pressure with and without the vacuum hose attached.

 

[EEvette]

I did check for spark, I used a spark tester that I bought from a local automotive store. However, I wasnt sure to what setting to adjust the screw to. It ranged from 10 to 40 SE. On the 35 setting I got a spark upon starting and not during cranking. The spark would not jump the gap every time(engine running). Has anyone used these, what setting should I use?

Thanks for all the help.

 

[TedC]

EEvette, Now we are getting somewhere. I'm hoping those with more knowledge on the L98 ignition will speak up. My 1989 has no issue jumping the gap during cranking all the way up to 40 using a similar tool. I think the 40 setting represents 40,000 volts, and the stock L98 coil can produce some really high voltages.

 

[EEvette]

TedC, I wonder if its ignition related. Like I said, once the engine started the spark would jump the 40 gap inconsistently.....when I reduced the distance to about 20 I would get consistent sparks.

Anyone that knows more about this please speak up.

 

[TedC]

EEvette, I would think a spark strong enough to reach 20 should be enough to ignite the fuel. If I understood your prior post, you did not see any spark of any quality during crank. Please confirm the long start when engine is both cold and hot.

Some addition info on pre 1989 L98s...
WHAT THE ECM - PCM DOES: The 1985-1988 TPI system utilizes the following sensors and devices to control the engine: Mass Air Flow Sensor, Manifold Air Temperature, Coolant Temperature, Oxygen Sensor, Throttle Position Sensor, Cold Start Switch, Cold Start Injector Fuel Injectors, Idle Air Control Valve, Distributor Electric Spark Timing, (Module in distributor TPI) Electric Spark Control, Module and Knock Sensor.

When the starter is engaged and the coolant temperature is less than 100 deg F. The cold start injector provides a spray of fuel, of 8 seconds duration max, to each cylinder via a air distribution system built into the intake manifold. If the engine temperature is greater than 100 deg F, the cold start injector is disabled by the cold start switch. Upon startup the ECM utilizes information in the calibrator to establish the initial pulse rate for the injectors and the engine starts. At this time the engine is operating in open loop mode and will continue to do so until the engine warms up. After the warm up period the ECM scans the sensors, if all sensors are operating and within their proper range, the engine then goes into closed loop operation.

 

[EEvette]

tedC,

Here are a few things I have noticed:

Starts cold with no problems.

After being driven, lets say I go to the store and I come back to start it, takes a while 5 to six seconds. If I turn it off once it starts (hot) and immediately turn the key, it starts. I guess it has to sit for a while after being driven for the problem to surface.

With the gap set at 40, no spark during cranking (hot) on cylinder 1 but engine eventually started.

Once started spark would not jump 40 gap.

I guess I need to check fuel pressure to see if there is any loss from the time I turn the key, to maybe ten minutes after in the off position. I will do that as soon as I get home.

 

[TedC]

EEvette, The results of the pressure test are key. My 1988 would not start right away after sitting hot for 5-20 minutes. Had to crank for 5+ seconds. It would start fine hot if started right after shut off or I waited a few hours. Leaking injectors can cause a rich condition that requires the extra cranking to clear the combustion chambers. What I don't understand is why you are not seeing any spark during this situation.