98 Astro AWD Intermittent Starting Problem

This has been a real tricky problem to troubleshoot. Failure to start seems to coincide with sitting for a day or two without use. The engine will crank and sputter slightly after the ignition is disengaged as if it's getting too little spark or fuel. The coil, distributor, and rotor were just replaced. I checked for spark and it looked good. I purchased a fuel pressure gauge and found that with the pump on (ignition on, but not cranking) the pressure was 62 psi for a couple of seconds, coincident with the hearing the pump run, then drops to 56 psi when the pumps stops.which is in spec but at the bottom of the passing range, according to the manual. This past weekend I changed the fuel filter and it started right up and ran well, this after not starting for the last 2 weeks, trying to start it every day and also three times before changing the filter that day. The fuel pressure reading when it was starting remained the same as when it didn't. After sitting for 2 days it wouldn't start again. My thinking is the valve inside fuel pressure regulator may be getting stuck (so I have pressure but no flow) or the injector spray pattern may be out of sync with the crankshaft. Any suggestions would be greatly appreciated.

This has been a real tricky problem to troubleshoot. Failure to start seems to coincide with sitting for a day or two without use. The engine will crank and sputter slightly after the ignition is disengaged as if it's getting too little spark or fuel. The coil, distributor, and rotor were just replaced. I checked for spark and it looked good. I purchased a fuel pressure gauge and found that with the pump on (ignition on, but not cranking) the pressure was 62 psi for a couple of seconds, coincident with the hearing the pump run, then drops to 56 psi when the pumps stops.which is in spec but at the bottom of the passing range, according to the manual. This past weekend I changed the fuel filter and it started right up and ran well, this after not starting for the last 2 weeks, trying to start it every day and also three times before changing the filter that day. The fuel pressure reading when it was starting remained the same as when it didn't. After sitting for 2 days it wouldn't start again. My thinking is the valve inside fuel pressure regulator may be getting stuck (so I have pressure but no flow) or the injector spray pattern may be out of sync with the crankshaft. Any suggestions would be greatly appreciated.

You may be weak on fuel pressure . even a couple of lbs low on a cold start will cause a no start.
Double check cold start cranking fuel pressure. If under 63-62 lbs you have problems.
one test is to give it a squirt of carb cleaner not starting fluid. If it starts then you have a fuel pressure problem.
Run the full fuel pressure test and post back pressures.
Here is the guide lines on testing.
Hard to start cold.
Check cold start fuel pressure.
Check engine running fuel pressure.
Check engine running on the road fuel pressure.
Then shut it off and watch for fast leak down.
Pinch off at rubber part or block off return line and check full pressure.
Later V6 and V8 gm engines should have 60-66 fuel pressure.
Cold start should be 64-65 lbs of pressure.
If you do not have full fuel pressure on a cold start the injectors will not squirt fuel.
Do not leave home without it.
Engine running should be 60-66 lbs pressure depending on engine load.
Full pressure with return pinched off should be 75-85 or more.
And if it has a fast leak down after shut off you have a leak.
Post back fuel pressure readings.

Thanks for the feedback. The return line does not seem to have a rubber portion, can you suggest a way to block the high pressure metal line? If I measured 62 psi on cold crank (with no start) then block the return line and it starts (with the 75-85 psi), does this mean it's the pressure regulator or fuel pump?

Thanks for the feedback. The return line does not seem to have a rubber portion, can you suggest a way to block the high pressure metal line? If I measured 62 psi on cold crank (with no start) then block the return line and it starts (with the 75-85 psi), does this mean it's the pressure regulator or fuel pump?

No.
The 75-85 is only a check on the capable full pressure of fuel pump.
If you can not find the rubber return line check full pressure by plugging return line or just or the true full pressure can be taken direct at the end fuel filter.
What are the pressure readings that you have done.
What are your cold start pressure readings?
Post back what you have.
MT

My '97 did about the same thing, with the marginal fuel pressure.
I used the starting fluid method. Just a 1 second squirt down the air pipe after the air filter. It seems these vans need more pressure to start than to run, so with the fluid it started, and then ran fine. I replaced the pump, it works fine. And yes, I changed the filter as a 1st troubleshooting method. (cheap insurance)

Ok, just tried blocking the return line and I measured approx. 75 psi. Van still doesn't start. Then I tried replacing fuel pressure regulator, and it doesn't start. My mechanic measured the electrical impedance of the injectors the two recently replaced ones measured 12.8 Ohms. The four old ones measured 11.4 Ohms, and the four new ones he wants to put in measured 12.8 Ohms. He's going to try it with the four new ones. I don't think this is the problem as resistance can be a little different between different injector manufacturers and batchs. I'm leaning toward the computer, even though the reader is saying the injectors are being driven at the right pulse width modulation. I doubt the computer is looking at the very output of the injector drive circuit. But if something did go on the computer it would have to be common to all injector drivers.

Ok, just tried blocking the return line and I measured approx. 75 psi. Van still doesn't start. Then I tried replacing fuel pressure regulator, and it doesn't start. My mechanic measured the electrical impedance of the injectors the two recently replaced ones measured 12.8 Ohms. The four old ones measured 11.4 Ohms, and the four new ones he wants to put in measured 12.8 Ohms. He's going to try it with the four new ones. I don't think this is the problem as resistance can be a little different between different injector manufacturers and batchs. I'm leaning toward the computer, even though the reader is saying the injectors are being driven at the right pulse width modulation. I doubt the computer is looking at the very output of the injector drive circuit. But if something did go on the computer it would have to be common to all injector drivers.

You need 3 things.
Compression
Good hot blue spark to all plugs.
Good gasoline and proper fuel pressure. 63-64 lbs.
If you have all 3 then move on to injector pulse to all injectors.
I think each injector is on a seperate driver on that one.
Check for pulse to all of them.
MT

Just curious why you suggest using carb cleaner and not starting fluid?

Just curious why you suggest using carb cleaner and not starting fluid?


Lot safer.
If you get a intake or engine full of starting fluid it can blow things all to hell.
Carb cleaner will start it if it is a fuel problem and lot safer.
Also in the good old days my kids used to get a couple of cans of starting fluid and get in the back end and have a good starting fluid spraying contest.
Good for a big blast if someone lights a match. :grinyes: :rofl: :lol:
MT

I just tried spraying carb cleaner in the air intake. I did it twice for about 6 seconds each. After a couple of more cranks there was a little more firing and I got two pops or blow backs out of the air intake. Does this indicate weak spark? Earlier you had mentioned that the spark should be blue, I saw yellow when I tested it last week. Since there's a new coil, rotor, and distributor cap, I thought maybe the plugs are not getting a good ground. While cranking I measured the voltage between the motor and frame to be 0.3 Volts and while not cranking the resistance to be 0.6 ohms. I'm at a loss what to do next. I'm going to check the coil next using the manuals troubleshooting algorithm.

Found a ground wire that attaches to the cross beam just in front of the fuel tank that does not appear to be making good contact. I first just tightened the grounding screw and found the Van started right away. So I pulled the screw and crimped washer and cleaned them it up and reattached to the frame. It's been starting and running fine now for 24 hours. If I get anymore no-starts it must be in the connector that this ground wire originates from which runs along this same cross-beam in front of the fuel tank. I'm now trying to identify this connector and ground and how they play into the starting sequence.

I thought I had metioned that.....
Yes, the nut on that ground had backed off about 1/4" on my van. Quite corroded too. I cleaned it up, and greased to prevent more corrosion. But i still had to change the pump.

Solution Found. I recieved an email from someone who had the same problem with a 99 AWD Astro. He suggested just replacing the cap and rotor. I took for granted that my mechanic replaced these two items after I requested him to do so. After inspecting the items I found the cap looked new but the rotor seemed older and one of it's screws (that mount it to the distributor) was stripped allowing some movement. Anyway I'm not sure if the stripped crew was the problem but replacing the cap and rotor has resulted in consistent starts. Thanks for the help guys.