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All right, I know this is an F-Body forum, but you guys are really knowledgeable, so I am hoping someone will recognize this problem. This might belong in Advanced Tech, I'm unsure. Moderators, if there is any problem with this being in General Tech, use your amazing Moderator skills to make things right. Anyway, here's the skinny. Buddy of mine has a 95 GMC Sonoma. It's got a 4.3L V6 with a 5 Speed Manual and 4x4. It's been acting extremely weird for a week or two now. We were driving (in the general direction of Point Pleasant, WV, aka: Mothman Territory) the truck started acting up, and it's been doing it since that night. Here are the symptoms:
While idling, the oil pressure gauge sets right on 40psi.
Apply throttle and the pressure jumps to 60psi.
Shove in the clutch, and it will drop, sometimes as low as 20psi.
The truck has plenty of oil, he just changed it the other day, the dipstick reads fine, and there are no leaks underneath.
When pulling out the truck hesitates, the oil pressure gauge reads around 25-30psi, and then it starts to shimmy really badly.
During the shimmy, the truck acts as though the key has been turned off, you can't tell its running until you try to start it again, and grind the starter.
When the shimmy takes place, the speedometer jumps to about 60mph (when we are just pulling out), the ABS light, Brake light, Seatbelt light, and a couple others start going crazy on the dash.
When it's going through all this, the headlights start cutting out, as if his Daytime Running Lights are shutting off when turning the vehicle off, but these are his regular headlights while the truck is running.
There are a few other things, but can't think of them offhand.
So, now, I need a diagnosis. I think it's one of a few things;
Number 1: Dead Oil Pump. It could be the root of this problem. Long shot: With its demise, the ECU?/PCM?/whatever, is telling the engine to shut off due to the low oil pressure. (I don't know if this feature was part of the programming on the 95's, but have heard of it in a newer Silverado).
Number 2: Bad Oil Pressure sensor? I don’t know too when it comes to the sensors, but it's a possibility. Right? If it's bad, it could be sending the computer an erroneous pressure reading, and thus causing the same long shot I mentioned in the last scenario. Computer shuts the truck off to avoid causing damage? Again, I don't know if the '95 Sonoma's have this feature (know someone who got a Lemon of a Silverado, dealerships wouldn’t work on it till something serious went wrong, so he drained the oil and tried and blow it up. But the truck wouldn’t run without oil pressure. I think he said something about reading the manual later, only to find that the computer won’t let it run with no pressure, to avoid damage)
Number 3: Electrical Problem. We don’t even want to go on a wild “Electrical Problem” goose chase. He will probably sell the truck before he goes through that.
Number 4: Who knows? All help is appreciated guys. Any advice would be great.
Thanks to everybody who even made it through all that, I know it’s a long read. Please help.
[ May 07, 2003: Message edited by: silvachris1 ]</p>
While idling, the oil pressure gauge sets right on 40psi.
Apply throttle and the pressure jumps to 60psi.
Shove in the clutch, and it will drop, sometimes as low as 20psi.
The truck has plenty of oil, he just changed it the other day, the dipstick reads fine, and there are no leaks underneath.
When pulling out the truck hesitates, the oil pressure gauge reads around 25-30psi, and then it starts to shimmy really badly.
During the shimmy, the truck acts as though the key has been turned off, you can't tell its running until you try to start it again, and grind the starter.
When the shimmy takes place, the speedometer jumps to about 60mph (when we are just pulling out), the ABS light, Brake light, Seatbelt light, and a couple others start going crazy on the dash.
When it's going through all this, the headlights start cutting out, as if his Daytime Running Lights are shutting off when turning the vehicle off, but these are his regular headlights while the truck is running.
There are a few other things, but can't think of them offhand.
So, now, I need a diagnosis. I think it's one of a few things;
Number 1: Dead Oil Pump. It could be the root of this problem. Long shot: With its demise, the ECU?/PCM?/whatever, is telling the engine to shut off due to the low oil pressure. (I don't know if this feature was part of the programming on the 95's, but have heard of it in a newer Silverado).
Number 2: Bad Oil Pressure sensor? I don’t know too when it comes to the sensors, but it's a possibility. Right? If it's bad, it could be sending the computer an erroneous pressure reading, and thus causing the same long shot I mentioned in the last scenario. Computer shuts the truck off to avoid causing damage? Again, I don't know if the '95 Sonoma's have this feature (know someone who got a Lemon of a Silverado, dealerships wouldn’t work on it till something serious went wrong, so he drained the oil and tried and blow it up. But the truck wouldn’t run without oil pressure. I think he said something about reading the manual later, only to find that the computer won’t let it run with no pressure, to avoid damage)
Number 3: Electrical Problem. We don’t even want to go on a wild “Electrical Problem” goose chase. He will probably sell the truck before he goes through that.
Number 4: Who knows? All help is appreciated guys. Any advice would be great.
Thanks to everybody who even made it through all that, I know it’s a long read. Please help.
[ May 07, 2003: Message edited by: silvachris1 ]</p>
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