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How long does it take to get the air out?

Michaeljp86

Michaeljp86

EVIL GENIUS
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I had a valve cover leak so I fixed that and the leaky injector returns should be fixed too. Two days ago when I put it back together I let it run for maybe 20 min. Yesterday I started it again and it started like it had air in it still. I let it run for about 20min. Should all the air be out or if I still have problems does that mean more leaks?
 
I had this problem. sadly GMCTD isn't around anymore AND IS SORELY MISSED but he did a very long and detailed write up of why this happens at the old site but it never made it here. Basically it's because the PCM is cutting fuel to the cyls trying to balance out the motor making it harder to get the air out. The cures were either somehow disconnecting the OS and running it(not sure on that one and didn't do it that way) or justget it on the highway and pound it for a good 45 mins. That worked for me. When I got off the higway it sounded like a new truck. Just idling in the driveway or revving it for a few minutes won't do it. Trust me. I thought I f'ed something up big time changing my nozzles but it was just air. If you have leaks on the pressure side you will see them.
 
Mechanical ip. After 20 minuites of running the air should be out. Starting and stopping the engine with a rest inbetween will work the air out through the return line.Might want to try the clear fuel line on the return line coming off the IP. If you got bubbles you have air getting in somewhere. Check return line for blockage.
 
bk95td said:
Mechanical ip. After 20 minuites of running the air should be out. Starting and stopping the engine with a rest inbetween will work the air out through the return line.Might want to try the clear fuel line on the return line coming off the IP. If you got bubbles you have air getting in somewhere. Check return line for blockage.
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Good idea about the clear tube, I put clear hose on the return lines on my tractor and always had little bubbles. I thought it was normal then found a old dryrotted hose the hard way. :eek:

I cant drive the truck because the ground isnt froze anymore so its a mud bog here.
 
IMO if you cant get it running smootly within 1/2 min after thouroughly bleeding the system up to the IP and have fuel at the inj, you got a problem somewhere in the fuel supply ,tank to filter.
 
I started it today and it starts for a second and the quits. Then while cranking its sounds like its half way running. If you step on the throttle it will start but chug smoke.
 
It was running fine before you took it apart? How careful were you not to get dirt in the nozzles ? It could be airbound. Then again many times another problem surfaces at the same times and can drive you batty. May be best to start from scratch and make sure fuel supply to IP is good.
 
Before it was a hard start but worse. It had a leaky injector return and I thought that may be letting air in. It had a leaky valve cover so I fixed both problems.
 
The truck runs and still pumps fuel out the top of the filter so the fuel is there.

What do you mean the IP is packing it in?

I started the truck today and I didnt have to step on the throttle. It started right up but smoked like a locomotive and shook like its missing for about 20 seconds then it was running on all 8. Its runs perfect its just the starts.
 
What kind of fuel pressure do you have at the filter manager?

Having several glo plugs not working might also cause this problem on cold startup. Does it do the same if you plug in the block heater for a couple hours?

Have you tried turning up the fuel a bit?
 
Acesneights1 said:
I'm not real familiar with the 92's. Is the LP Electric or Mech ?
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Its electric, I think they had to go electric on all the 90s body style trucks because the frame or something was in the way of the mechanical pump.

buddy said:
What kind of fuel pressure do you have at the filter manager?

Having several glo plugs not working might also cause this problem on cold startup. Does it do the same if you plug in the block heater for a couple hours?

Have you tried turning up the fuel a bit?
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Ive never used the block heater, maybe Ill try it out tomorrow. If I start it while the engine is still warm from running it starts right up. This truck has the IP cranked up. Im not sure about the pressure, Ill see if I can find a gauge tomorrow.
 
Your LP should run during WTS and cranking (powered by the LP relay), and during operation (powered by the OPS). It could be it starts better from being warm or that it was recently primed with fuel
 
I guess the block heater is a good test. If its air in the system then it would still start hard with the block heater. The LP on this truck is wired up to the fuse block so the LP runs when the key is turned. I wish I would have checked the glow plugs while I had the turbo off.
 
Michaeljp86 said:
The truck runs and still pumps fuel out the top of the filter so the fuel is there.

What do you mean the IP is packing it in?

I started the truck today and I didnt have to step on the throttle. It started right up but smoked like a locomotive and shook like its missing for about 20 seconds then it was running on all 8. Its runs perfect its just the starts.
Click to expand...
Air in the system can cause that as well as bad glows.

I got 2 engines with a mech IP, both had the same symptoms at one time or another, both had good glows and no air in the system.
Both IP's where FFed. they dont seem to last beyond 125 k.
 
This truck has a brand new IP.

I plugged in the block heater for about 3 hours and it fired right up. I checked the glows on the drivers side with a ohm meter and they were ok I think. I just wonder if they are still the stock glow plugs under the turbo.

I still have the block heater plugged in, Im going to try it again tomorrow.
 
warm engine on first start helps then. The block heater sucks down some juice so may not want it on all night.

When you ohmed the GPs were they 1 ohm or less? And did you check to make sure there was 12V at them during WTS?

It can be GPs, or maybe retarding the injection helps it. Can try disconnecting the advance on a cold startup.
 
I didnt check for voltage at the glows. They were all 1 ohn but one was .6 from what I can remember. I guess Ill have to check them again.
 
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