Hi!

I’ve had problems with my 99 suburban K1500 for about 6 months now. The issues occurred after pulling overweight for a short distance in, unfortunately drive 4wd auto.

The truck started shattering around 49 and above mph, got worse uphill with the engine light flashing.

Found the yoke from the rear end of the transfer case to be cracked. Thought that was the cause, replaced it, and all of the u-joints - no improvement.

Then replaced the spark plug wires, spark plugs, the whole distributor with rotor and cap. Weird thing is that the issues changed, the car improved, but is still shaking uphill, worst around 35-40 mph, and it also sound a bit funky above 50, a deep rumbling, sort of.

I figured I put the car in a workshop instead of throwing in new parts with no clue.

They ran a diagnose, found nothing suspicious according to them. Got only one code, P0141 - Heated oxygen sensor. They suspected problems with the lock-up.
They pulled the oil pan from the tranny and found a lot of clutch and metal debris, and told me that was the cause of the problems.

SO, I sent the tranny to a transmission workshop with a good reputation. The tranny was checked, rebuilt and enforced. Good as new. New torque converter.

Back home the workshop reinstalled the repaired transmission. But guess what, apart from shifting a bit quicker, NOTHING has changed. Total 5000 USD for nothing.

Talked with the transmission guy, and his suggestion is that the real problem is the motor (5,7 vortec), that the motor misfires and causes problems with the lock-up.

Problem is that there are no codes indicating misfire, although I also suspected some kind of bad pre ignition or so, but I’m not a mechanic.

This is not the most common car in this country, and although the workshop is one of the few specialists in American trucks, they have no clue.

So if anyone here have any ideas, or have experienced someone similar, please share. I’m kind of desperate, and I’m not ready to give up on my truck yet.

 

Sooo, drove the truck to another workshop where they changed the fuel poppets with spider and so on. Also replaced one of the O2 sensors. They replaced the spark plugs again, as they thought they looked a bit worn- oddly enough, as they were recently replaced.
The truck didn’t improve at all, in my opinion it got a tad bit worse.
workshop checked the timing chain and gears, but seemed within normal range.
Engine is over all shaky, and the truck vibrates a lot uphill and engine seems tired.
It hasn’t stopped running, but it is just as if it’s about to when idling with warm engine.
No issues starting the truck.
Fuel pump has a high frequency noise, had this prior to these problems, but I figured I’d check the fuel pressure.
Ignition on/engine off: 59-60 psi while pump is heard, rests at about 52.
Engine on: 50psi
3000 rpm, no load: slightly under 50 psi
Cruising: 54-56psi
Uphil, about 2000 rpm: 58-59 psi.Very noticeable shaking as well.

Have tried to google what the fuel pressure should be, but it did not make me any wiser.

Are these normal readings, or could I assume that fuel pump is the main source of my problems?

I feel I have went through a lot of “could be”s, but nothing seems to help.