libtec
10-14-2004, 21:18
Thanks for looking! Yes this another hard starting question but I have a list of info that I hope can help narrow down what is going on.
I bought a 90 suburban with 120k +-, 6.2, auto, 4wd. The previous owner complained it had starting problems but ran fine when it did start. It had been sitting for two years and it took two brand new 900cca batteries and a little coaxing over two hours to get it going and he was correct, it runs great.
Here is the problem. I ran it for a week and a half without any sign of a starting problems after the initial fight to get it going. I was able to go out in +25 temps and cycle the glow plugs through the intital 5-6 secs and the motor would kick on within a second or two of cranking without plugging in the block heater or oil pan heaters at all. I ran this way doing flawless hot and cold starts for a week and a half till I shut it down one day (+55F) for a half hour and it refused to start again till I charged the batteries for ten minutes. Since then it has been a bear to start when cold (+25 to +50) but starts perfect when warm.
What have I tried to fix to cure this problem? Since I was running a questionable alternator I replaced it with a wilson recondition that is showing excellent voltage and is keeping the batteries topped. I replaced the glow plug controller/solenoid since the old one would chatter after the initial 5 secs at start up. I replaced the starter motor and gained a significant amount of cranking rpm and some success at cold starts (but not cured). I have tested all the glow plugs twice (Lucas DSO94) and all heat up within 4-5 secs. I have checked each glow plug lead with a plug and a jumper to ground operated through the solenoid and have heat on all 8. I have 12 volts at the orange wire from the thermal cut out to the plug module 4 pin connector. I believe the cold advance to my IP is operating since I can hear the solenoid engage and release when I pull the green lead and the motor sound and operation is slighlty different till the temp rises. I did replace the fuel and air filter on the first day we got it running. The IP is a reman from a reputable local shop that specializes in Ip's and I have had the pump timing professionaly checked and it showed to be set correct.
Even with all the above mentioned questionable parts in place this truck started flawlessly and with no apparent cause decided to instantly become a problem starter, but still an excellent runner. What could cause this?
The hot compression does have a variance from 410psi +- on the front two, 380 +- on the middle four and 320 +- on the rear two. This has been the same from day one and was rechecked this last weekend. So even though the cylinders aren't perfect they still were allowing the perfect starts I was experiencing ( I do plan on a rebuild next summer ).
In short, I have what appears to be a properly functioning glow plug system, a not perfect but still very strong motor, proper fuel delivery at the proper time, good cranking speed, plenty of air to burn, all the basic elments that a motor needs to run, so why the sudden problem?
I have read that you can bypass the controller by grounding the blue wire, but I see this as a band-aid avoiding the core problem and I don't want expanded plug ends.
I only started to learn about diesels three weeks ago and have only had a couple hours to learn and trouble shoot what I have described this far. The man I was relying on to help and teach me about this motor, my father in law, left us two days after we brought this truck back to life. He was a master mechanic, a jack of all trades and a true craftsman in everything he did, he is with God now. The last thing I ever did with him was test run this truck and he said it had a lot of potential, but a couple of bugs to work out. He said we'd figure the bugs out next weekend.... I'm getting some of them, but I hope some one out there can pinpoint the others he was thinking about because he never told me.
Thanks in advance. John.
I bought a 90 suburban with 120k +-, 6.2, auto, 4wd. The previous owner complained it had starting problems but ran fine when it did start. It had been sitting for two years and it took two brand new 900cca batteries and a little coaxing over two hours to get it going and he was correct, it runs great.
Here is the problem. I ran it for a week and a half without any sign of a starting problems after the initial fight to get it going. I was able to go out in +25 temps and cycle the glow plugs through the intital 5-6 secs and the motor would kick on within a second or two of cranking without plugging in the block heater or oil pan heaters at all. I ran this way doing flawless hot and cold starts for a week and a half till I shut it down one day (+55F) for a half hour and it refused to start again till I charged the batteries for ten minutes. Since then it has been a bear to start when cold (+25 to +50) but starts perfect when warm.
What have I tried to fix to cure this problem? Since I was running a questionable alternator I replaced it with a wilson recondition that is showing excellent voltage and is keeping the batteries topped. I replaced the glow plug controller/solenoid since the old one would chatter after the initial 5 secs at start up. I replaced the starter motor and gained a significant amount of cranking rpm and some success at cold starts (but not cured). I have tested all the glow plugs twice (Lucas DSO94) and all heat up within 4-5 secs. I have checked each glow plug lead with a plug and a jumper to ground operated through the solenoid and have heat on all 8. I have 12 volts at the orange wire from the thermal cut out to the plug module 4 pin connector. I believe the cold advance to my IP is operating since I can hear the solenoid engage and release when I pull the green lead and the motor sound and operation is slighlty different till the temp rises. I did replace the fuel and air filter on the first day we got it running. The IP is a reman from a reputable local shop that specializes in Ip's and I have had the pump timing professionaly checked and it showed to be set correct.
Even with all the above mentioned questionable parts in place this truck started flawlessly and with no apparent cause decided to instantly become a problem starter, but still an excellent runner. What could cause this?
The hot compression does have a variance from 410psi +- on the front two, 380 +- on the middle four and 320 +- on the rear two. This has been the same from day one and was rechecked this last weekend. So even though the cylinders aren't perfect they still were allowing the perfect starts I was experiencing ( I do plan on a rebuild next summer ).
In short, I have what appears to be a properly functioning glow plug system, a not perfect but still very strong motor, proper fuel delivery at the proper time, good cranking speed, plenty of air to burn, all the basic elments that a motor needs to run, so why the sudden problem?
I have read that you can bypass the controller by grounding the blue wire, but I see this as a band-aid avoiding the core problem and I don't want expanded plug ends.
I only started to learn about diesels three weeks ago and have only had a couple hours to learn and trouble shoot what I have described this far. The man I was relying on to help and teach me about this motor, my father in law, left us two days after we brought this truck back to life. He was a master mechanic, a jack of all trades and a true craftsman in everything he did, he is with God now. The last thing I ever did with him was test run this truck and he said it had a lot of potential, but a couple of bugs to work out. He said we'd figure the bugs out next weekend.... I'm getting some of them, but I hope some one out there can pinpoint the others he was thinking about because he never told me.
Thanks in advance. John.