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91 GMC C3500 6.2L J code
4L80e trans 4:56 rear end.
33,000 original miles.

Short run down is that I bought this truck two years ago and up until the transmission went it kept a pretty normal pattern of things

Oil Pressure cold would start high 3/4 of the gauge (60 psi?) and then settle to about in the middle at 40. '
oil pressure warm would stay about about 40 even with no load at idle.
Coolant temp would sit below 210 (center) unless going up a mountain then it would hit 210.
Voltage would fluxuate between 12 and 14

I had a used transmission put it since the other one failed with 31000 original miles on it. I had to drive it from NH to SC and noticed things are a bit different. Noticed about 150 miles in that there were some subtle differences

Oil Pressure cold started at that 60psi range but after hitting operating temp and driving for a while it would sit at 40 under load and then drop to 20 (or the quarter mark) when at idle.
Coolant sits at 210 under any driving and goes back to 190ish at idle
Voltage stays around 12

I also have a lot more black smoke (soot) when I have to floor it to get it up a hill. I have a lot less power than I remember before the transmission swap. Also a strange almost groaning noise once it gets warmed up at cruising speeds. sometimes a small hiccup/buck or hesitation on acceleration if in over drive.

I changed the oil upon arrival and didn't see any metal in it so I hope I didn't murder it. Air filter is clean, Fuel filter and electric lift pump were replaced right after the transmission.

Please help with any advice. I asked a couple shops around here to look at it and they want nothing to do with it for a litany of reasons.

Thanks!
 

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Well my first question is how do you know for sure the mileage you posted is correct and the odometer hasn't turned over, and how old is the IP & injectors, any dirty fuel been run in it, Hows the timing, a db2 pump can be hard to time for someone not us to doing it, their are several things that could be adding up...

The higher temps, lower oil pressure lead to a motor with way more miles than you think yours has, what oil weight are you using, what oil filter...

You should not be running 210* just riding down the road, use a AC thermostat only !!!!!!!!!!!! and make sure the cooling stack is clean, might need to remove the radiator and pressure wash the fins and the ac condenser, etc... your fan clutch may be tired, their is a higher flowing water pump for the 4 bolt fan blade, their is a post in the 6.5 section on this subject with part numbers..

Be very cautious sending your injection pump to be rebuilt or checked, a brand new updated pump can be purchased for the same cost as a rebuild of unknown quality, message me if you want more info on pumps...
 

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Your lift pump could sound like it's pumping but not be doing anything causing the IP to pull fuel instead of being feed fuel, this will cause poor response and smoke, ie, making the pump work harder and not doing it's job as good as it could..
 

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Discussion Starter #6
Well my first question is how do you know for sure the mileage you posted is correct and the odometer hasn't turned over, and how old is the IP & injectors, any dirty fuel been run in it, Hows the timing, a db2 pump can be hard to time for someone not us to doing it, their are several things that could be adding up...
All I have to go on is the the documentation provided from the US Government and the utility company I bought it from. From what I gathered this truck sat in Saudi Arabia and Germany, then got turned over to a power company in Georgia where it pulled stuff around their yard.

The higher temps, lower oil pressure lead to a motor with way more miles than you think yours has, what oil weight are you using, what oil filter...
15w40 Valvoline or Chevron Delo. Ran John Deere 50 plus II once. I used a wix 51061 and a now a delco PF1218

I have to reiterate it didn't start doing this until just recently. I drove it from Georgia to NH with zero issues with temp and oil pressure. It was my daily driver until the transmission let go. Before the trans job it never went below 40 psi, temp never got to 210 without a hill climb. Only after I put the transmission installed at a repair shop and drove it from NH towards SC did it start with the fluctuations.

You should not be running 210* just riding down the road, use a AC thermostat only !!!!!!!!!!!! and make sure the cooling stack is clean, might need to remove the radiator and pressure wash the fins and the ac condenser, etc... your fan clutch may be tired, their is a higher flowing water pump for the 4 bolt fan blade, their is a post in the 6.5 section on this subject with part numbers..
noted

Be very cautious sending your injection pump to be rebuilt or checked, a brand new updated pump can be purchased for the same cost as a rebuild of unknown quality, message me if you want more info on pumps...
I'll send you a message.

I was just hoping I could pinpoint one or two things to get it back running like I remember. I don't have the cash to start throwing parts at it.

Thanks,
 

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Your lift pump could sound like it's pumping but not be doing anything causing the IP to pull fuel instead of being feed fuel, this will cause poor response and smoke, ie, making the pump work harder and not doing it's job as good as it could..
It's a month old. I'm guessing it could be defective out of the box?

The old one that was still good is sitting somewhere on a moving truck.
 

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What vehicle did the used transmission come out of?

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From what I remember it was an 89-90 3/4 ton with a 6.2
Ok just wanted to make sure something like a non diesel torque converter wasn't part of your problem.

I'm sure something got messed with or didn't get put back right when the tranny was put in

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Ok just wanted to make sure something like a non diesel torque converter wasn't part of your problem.

I'm sure something got messed with or didn't get put back right when the tranny was put in

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I'm honestly unsure. Is there a way to tell by stamping numbers or any RPO's on the transmission itself?

That wouldn't surprise me and that's really not good news.
 

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I'm honestly unsure. Is there a way to tell by stamping numbers or any RPO's on the transmission itself?

That wouldn't surprise me and that's really not good news.
Doubt it since it was used on both gas and diesel applications. As far as I know the only difference is a different torque converter so maybe a stamp on the TC could tell you? Not really sure I'm not an expert on transmissions.

With the other symptoms you mentioned the problem is likely somewhere else but it might be worth looking into just to be sure

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91 GMC C3500 6.2L J code
4L80e trans 4:56 rear end.
33,000 original miles.

Short run down is that I bought this truck two years ago and up until the transmission went it kept a pretty normal pattern of things

Oil Pressure cold would start high 3/4 of the gauge (60 psi?) and then settle to about in the middle at 40. '
oil pressure warm would stay about about 40 even with no load at idle.
Coolant temp would sit below 210 (center) unless going up a mountain then it would hit 210.
Voltage would fluxuate between 12 and 14

I had a used transmission put it since the other one failed with 31000 original miles on it. I had to drive it from NH to SC and noticed things are a bit different. Noticed about 150 miles in that there were some subtle differences

Oil Pressure cold started at that 60psi range but after hitting operating temp and driving for a while it would sit at 40 under load and then drop to 20 (or the quarter mark) when at idle.
Coolant sits at 210 under any driving and goes back to 190ish at idle
Voltage stays around 12

I also have a lot more black smoke (soot) when I have to floor it to get it up a hill. I have a lot less power than I remember before the transmission swap. Also a strange almost groaning noise once it gets warmed up at cruising speeds. sometimes a small hiccup/buck or hesitation on acceleration if in over drive.

I changed the oil upon arrival and didn't see any metal in it so I hope I didn't murder it. Air filter is clean, Fuel filter and electric lift pump were replaced right after the transmission.

Please help with any advice. I asked a couple shops around here to look at it and they want nothing to do with it for a litany of reasons.

Thanks!
Since this was after a transmission replacement you might check the cooling lines from the trans to the radiator and see if they have full flow. Kind of a long shot but it might have happened.
 

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Does it go into overdrive?
If not then you still have transmission issues.
The electrical connector is troublesome in the early years, 89-91 if not plugged in correctly or grease/dirt in connectors, it could stay in limp mode.
No overdrive means it's going to run hotter adding heat to the radiator.
I'm no help with the engine but just finished rebuilding the 4L80E in my 91 GMC K2500, so I know a little about them.

Don

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Well first off ... the stock gauges and senders suck ... get mechanical ones or get it tested with master gauges.

ya 210 is a smidge warm but see above ... use only geni gm stats

Do you have a tach in this ?? I wonder if the previous trans wasn’t locking up the torque converter sand the new one is. TC lockup is a clutch in the converter which puts 100% of power from the engine to the tires like a standard. Once the tc is locked the tach won’t have any quick movements to throttle on off , it just climbs with engine speed only.
 
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