Apology in advance long thread. Hey guys, new to this forum because this truck has got me stumped. It’s a 94, 350TBI. And 4l60e. Truck is very solid , and I’d like to keep it around for awhile I’ve had it for about a month. So to start things off truck has a rough idle when cold, will come out of it after driving for a couple minutes. After about 15-20 minutes of driving around town, it starts the rough idle and has absolutely no power it starts running really rich. Can put the pedal to the floor and it revs way up, but doesent go any faster, sputters and backfires. Here’s the weird part. Throw it in neutral and shut the key off, crank it right back up and it will run amazing for about 5 minutes and then start losing power drastically until it’s doing that again. Fuel pressure is good, I checked base timing, changed map sensor. I don’t really know where to go from here. Coming from a strict ford diet I honestley have the slightest clue about these engines. Any tips or advice? Thank you!!
I hope this helps someone out there in GMT400 land!
I've spent 11 months trying to work out a very similar issue.
1994 with 4.3 V6.
Changed: TPS, MAP, IAC, Knock sensor, Temperature senders, PCV, EGR, Fuel pressure regulator(2x), Injectors when I rebuilt the TBI, New Distributor(2 times), Ignition control module(2x), Coil, fuel filter 2 times, new ground straps, O2 sensor, you name it!
ECM. It's timed dead on Zero advance with the brown wire unplugged(Mine is under the glove box).
All of those parts from the parts cannon and...
It only changed it's bad habits a bit but no midrange, just falling flat on it's face.
Misfire but no backfire/detonation.
No codes until finally a "lean" code!
Finally changed the FUEL PUMP last week...
PERFECTION!!!
It's a 4.3 and you would swear it's a 350 when not towing a heavy trailer/boat.
I'm running without a cat for now.
It's a joy to drive again!
FUEL PRESSURE!!!
It's the most important thing or one of the most important in the chain of factors that have to be perfect.
I didn't have tools to make a fuel pressure tester and learned the hard way.
I learned everything on the GMT400 site and it worked!
Thanks to everyone.
A note: Before changing the fuel pump I unplugged the temperature sensor at the thermostat and it ran better!
Until it warmed up.
FYI, I used all ACDELCO replacement sensors/parts.
I got 2 bad dist. caps that are Acdelco and actually read MADE IN THE USA on the tops!!!
I'm 100% American and that pissed me off.
The terminals inside were twisted right out of the box.
You can't assume a new part is a "good part".
I swapped the rotor and cap for MSD and comparing the ACDELCO side by side, the MSD is built superior.
Was only $30 more than the Delco set!
Terminals are wider/thicker and the rotor swings closer to the terminals.
The only odd thing is that the temperature gauge runs up to 210, closes loop, then down all the way to 135 or so?
I'm in Southern California so it never really gets cold out.
When I check the thermostat with a infrared temp sensor it's proper at 195.
I've changed that temperature sensor 2x and have the same result.
I'll let that go for now.
I'll try to add some pics.
In my experience, use ACDELCO/DELPHI parts.
Pete!
