'98 Astro will NOT start cold, will start hot

[cell315]

’98 Astro will NOT start cold—will start hot.

22,000 miles on the V-6. This vehicle sat around outside in the sun (in Honolulu), a long time before I bought it. It used to start OK when I first got it, but now it will not start first thing in the morning. It will try to start for a revolution or two and that is the end of it. It acts like it is not getting fuel. After it is in the sun for an hour it will start every time and then runs fine the rest of the day with no problem at all. If I start it at 10:00 PM and run it for 5 or 10 minutes, it will usually start first thing in the morning because something in the engine is still warm enough. We aren’t talking cold mornings here. Cold is 60 degrees F. That is about as cold as it ever gets. I put a thermometer under the engine hood and when the ambient temperature is 75 to 80 degrees F. the under-hood temperature is between 100 and 105 degrees F. This is when the engine will start every time without fail.

This is what I have done: I checked the fuel pressure first. A friend came by with his fuel pressure gauge and it read 62 or so psi. He said it looked OK to him. I took the van to a supposedly reputable repair shop. They told me it would be $77. to diagnose the problem. They called three days later and wanted more $ because they did not have it figured out yet. I told them to stop what they were doing. I went down there and had words with the owner, and he said that he did not know how I was going to get my van out of his parking lot because it would not start. By this time it was late afternoon and it had been sitting in the sun. It started right up. This cost me $85 for nothing—but one thing he said was that the fuel pressure was OK.

So now I suspected the ignition—high voltage leakage. I tried starting it at night and sure enough there were some light flashes near the coil. When I removed the coil, there was evidence of corona discharge to ground. I replaced the coil, ignition wires (with expensive ones), rotor and distributor cap; oh, and the spark plugs as well. I really thought this would solve the problem. It did not solve anything. Then I took a heat gun and carefully warmed up various points on the engine, such as the distributor, coil, air intake, etc. thinking that if there was a moisture problem, this might show me where it is. No luck. I could not simulate the heat of the sun on the engine compartment. I checked the resistance of the air temp sensor (thermistor) and it seemed to be in the ball park. At this point I do not think humidity or moisture is the problem.

Then I bought my own fuel pump pressure tester and went over that again. As soon as the key is turned on, the fuel pressure jumps right to 62 psi. When the pump shuts off (reaches pressure), the reading drops to 55 psi. It stays there but slowly drops. In five minutes it will be down to 45 psi.

All the time the engine is cranking, the pressure reading stays right around 61-62 psi. If it starts, while the engine is running the fuel pressure hovers between 50-55 psi. depending on the throttle position and engine RPM.

No OBD error codes are ever set. I give up.

[Matrixx]

Hi cell315
The pressure drop is to much over that time period cell315, 2 pounds in 10 minutes (or close to that) is the given specs. for pressure requirements. I don't "think" that is your problem though. If you have a heat gun and you know it starts every time when it's warm out and heat related, maybe hit the Temp Sensor (next to the thermostat housing) on the front of the motor as well as the EGR valve (front Intake by thermostat housing), Fuse Block, and Computer. If you still don't get any results, then hit the Crank Shaft Position Sensor located on the lower part of the crank shaft pulley on the passenger side on the front of the motor. You get access to it under the front of the vehicle. Maybe even start hitting plug-ins leading to the motor from the computer.

If everything with the heat gun fails, then you will need to start pulling wires off to make sure your getting spark from the coil to the cap and then from the cap to the spark plugs to start with. This is not my normal recommendations, but if it's heat related and you have a heat gun I'm sure you will at least find the area where to start looking anyways. The process of elimination is important here. Hope this helps, please keep us updated, Thanks.

[astro355]

Do you have any access to a decent scan tool?

Two things I would be curious about are if the injectors are firing and if there is a signal coming from the crank position sensor.

[Matrixx]

Hi cell315
Just another suggestion as well with the heat gun, is to hit the ignition switch with it and see what happens. Don't over heat it though. If it's been sitting for a long period of time, then dampness and corrosion could have entered into it as well. Just a thought. Astro355 has some good suggestions as well. Mine are a bit unorthodox for this particular post, but I feel it will find the problem (or problem area) quicker as you say it is heat related (worth a try anyways). Please keep us updated, Thanks.

[astro355]

I have given this a little more thought. You have tested for fuel pressure but you don't actually know if the injectors are fired. What you could do to test it is get some propane. While the van is being turned over, put some propane down the intake. If it starts, you would then know that you are not getting any fuel into the cylinders. I would used a propane torch or anything else that has a valve on it so you can control the flow of propane.

[cell315]

Hi cell315
The pressure drop is to much over that time period cell315, 2 pounds in 10 minutes (or close to that) is the given specs. for pressure requirements. I don't "think" that is your problem though. If you have a heat gun and you know it starts every time when it's warm out and heat related, maybe hit the Temp Sensor (next to the thermostat housing) on the front of the motor as well as the EGR valve (front Intake by thermostat housing), Fuse Block, and Computer. If you still don't get any results, then hit the Crank Shaft Position Sensor located on the lower part of the crank shaft pulley on the passenger side on the front of the motor. You get access to it under the front of the vehicle. Maybe even start hitting plug-ins leading to the motor from the computer.

If everything with the heat gun fails, then you will need to start pulling wires off to make sure your getting spark from the coil to the cap and then from the cap to the spark plugs to start with. This is not my normal recommendations, but if it's heat related and you have a heat gun I'm sure you will at least find the area where to start looking anyways. The process of elimination is important here. Hope this helps, please keep us updated, Thanks.

Hi Matrixx,
Thank you for your help. This may take some time. At least for now this thing is being consistent. The warmer the air temperature gets, the more the engine sounds like it wants to start. It will fire for a few revolutions and not run. When I was changing ignition components, the van was facing North, and the sun never hit the front. It would not start. I pushed it around in the yard until it was facing the sun, and within an hour, it started. Yesterday as it was getting warmer it almost would start. At this point I took my heat gun and heated that sensor (or whatever it is) that is next to the thermostat housing. When I heated it up, the engine started right up. However, I need to do this again in the same sequence when it is cooler outside to make sure that this is the culprit. By the way, it has five wires coming out of it. What exactly does it do, and how is it removed??? Another thing I am thinking is that whatever it is that is getting warm and allowing the engine to start, is probably at the top of the engine, fairly near to the engine hood. This leaves out the crankshaft position sensor, I think. I did try heating the air temp sensor just behind the air-flow sensor, and it as well, and nothing changed. I do not have a Haynes or other repair manual for this vehicle and am in pretty much in the the dark concerning all the magical things that are everywhere on this beast. I grew up with ignition points and carburetors and I hate this stuff.
Thanks again for your input.

[cell315]

Do you have any access to a decent scan tool?

Two things I would be curious about are if the injectors are firing and if there is a signal coming from the crank position sensor.

Hi astro355,
No, I don't have anything except a bare-bones code reader. Is that what you meant?
Thanks for your input.

[cell315]

Hi cell315
Just another suggestion as well with the heat gun, is to hit the ignition switch with it and see what happens. Don't over heat it though. If it's been sitting for a long period of time, then dampness and corrosion could have entered into it as well. Just a thought. Astro355 has some good suggestions as well. Mine are a bit unorthodox for this particular post, but I feel it will find the problem (or problem area) quicker as you say it is heat related (worth a try anyways). Please keep us updated, Thanks.

Hi Matrixx,
I tried this with the ignition switch, and it did not help. Actually there is not much corrosion around except aluminum oxide starting to show up on bare aluminum tubes and other parts.
This van was totally baked in the sun for some years judging by the deteriorated paint and dried out window gaskets front and rear. It belonged to the U.S military. Now it is located on the dry side of the island (of Hawaii). This is another reason that I think the problem is strictly temperature related.
Thank you very much for your help.

[cell315]

I have given this a little more thought. You have tested for fuel pressure but you don't actually know if the injectors are fired. What you could do to test it is get some propane. While the van is being turned over, put some propane down the intake. If it starts, you would then know that you are not getting any fuel into the cylinders. I would used a propane torch or anything else that has a valve on it so you can control the flow of propane.

Hi astro355,
Thanks for your continued input. Before I knew any better, I tried spraying something like starter fluid into the air stream. I could not tell if if was doing anything or not. It did not seem like it. I will try the propane though. That seems like a lot better idea. Will this thing run with the air intake totally disconnected?
There is one other thing: At the time I was measuring the resistance of the front temperature sensor, and found it to be OK, I just disconnected the two-wire plug going to it, and the engine still started and ran fine. It was already the middle of the day by then.

[Matrixx]

Hi cell315
Thanks for the update. Can you be more specific to the location of that 5 wire plug-in (and the color of the wires) you say you heated then fired right up? I can look it up and let you what it is exactly. I was raised on points and carbs as well, this new system can be overwhelming at times.

Once you understand the method on how this electronic stuff is set up, it isn't hard to figure out what goes where, their is an order to it. Just takes time to understand it. If you could let me know on the question I asked that would be great, then I can give you an answer to it, Thanks.

[astro355]

Hi astro355,
No, I don't have anything except a bare-bones code reader. Is that what you meant?
Thanks for your input.

No, not a code reader. A scan tool like a Tech 2 or something. On those scan tools, you can monitor the sensors to see what they are doing. Hell, you can even watch the pulse width on the fuel injectors.

[cell315]

Hi cell315
Thanks for the update. Can you be more specific to the location of that 5 wire plug-in (and the color of the wires) you say you heated then fired right up? I can look it up and let you what it is exactly. I was raised on points and carbs as well, this new system can be overwhelming at times.

Once you understand the method on how this electronic stuff is set up, it isn't hard to figure out what goes where, their is an order to it. Just takes time to understand it. If you could let me know on the question I asked that would be great, then I can give you an answer to it, Thanks.

Matrixx,


Sorry this took so long. I keep thinking that I will have discovered something new but I don't think so. That device with the 5 wires on it appears to go into the water jacket. It is just to the left of the thermostat housing. The colors of the wires are: Red, Slate, Brown, Black, White. There is a number also: 33672. It is tilted forward to the plane of the block about 45 degrees.
It could be a coolant temp sensor? Why five wires? I used the heat gun on this directly a couple of times and it did not help--so that is not the suspect. I have discovered a couple of things: The engine will start and run (when air temperature is warm enough) with the air temperature sensor disconnected. But it will set an error code, P0113, I believe. This is of course no help, to me at least. The air flow sensor can be removed from the intake air stream, and the engine will start and run but only for a few seconds. This is repeatable. If the engine does not start on the first couple of revolutions, because it is not warm enough, there is no way that I have found to make it start, except let the truck sit in the sun for an hour or so. In fact, if I did not Know any better, I would say that it seems as though it 'floods.' At least if it were a carbureted engine this is the only thing that I could come up with. Once it decides to start, it starts immediately and runs fine. I can drive it all day and the performance is absolutely normal in every respect. It always tries to start, fires a few times, but if it does not 'catch' right away, the ball game is over, and as I said there is nothing I have figured out that will make it start, except to wait for the sun. I tried the propane thing after it would not start, and this did nothing. I am not in a position to start buying replacement sensors, computer, etc. I am convinced that this is what the dealer would do, and it would add up to a lot of money, most of it probably unnecessary. (The only dealer here has had a bad reputation for service for many years. I had a nightmare going on with them over a new Chevy diesel (company) truck, that resulted in the company just getting rid of it because Chevy could not repair it).

I don't think that the crank position sensor is affected by changing ambient temperature. It is way down at the bottom of the engine, and the ambient temperature change here is not all that much to begin with. I am thinking that whatever is affected by the temperature would be something near the top of the engine, right under the hood. What about the air cleaner and associated housing etc? What about warmer air inside of all of that? What if it is not a sensor at all? My heat gun experiments have not been conclusive at all. If the engine really does 'flood' when cold, what could be the cause of that? I know very little about how the multi-port fuel injection systems function.
Thanks again for your help. Best regards,

[astro355]

I would have to tell you that the temp sensor you unplugged is at fault. If its sending a faulty signal back to the ecm, the ecm may think that its a lot colder than it really is and be running way too rich.

[cell315]

I would have to tell you that the temp sensor you unplugged is at fault. If its sending a faulty signal back to the ecm, the ecm may think that its a lot colder than it really is and be running way too rich.

That does make sense all right. But I did check the resistance of the sensor (thermistor), and it was right in the ball park according to the ambient temperature at the time. Is there a way to temporarily replace the sensor with a fixed resistance that will tell the ecm it is 75 degrees F. all the time?

[astro355]

Yeah, just leave it unplugged.

And when did you check the resistance, when it was cold (ambient temperature), warm (ambient temperature), or engine warm?

[Matrixx]

Hi cell315
Thanks for the update. Yes that 5 wire plug-in goes to your EGR valve. As Astro355 asked, how was the Temp Senor tested? Here is a chart that may help: