Hello, new to the forum so please excuse any ignorance.

I bought an '89 K3500 (7.4L 454) last week and it was running great at first- I ran it up one of my local canyons to test the engine and experienced intermittent loss of power at high speeds, which got worse until the truck stalled out when I came to a stop. Was able to get it started, but it would only stay alive when I pumped the gas pedal. Weirdest thing. Was finally able to sputter it to the nearby Chevy dealership pumping the accelerator (oddly enough, the engine seemed to fire briefly when I let off of the accelerator, and I had to keep pumping to keep this up), and they ran a diagnosis and said that it has fuel pressure, but that the injectors were dumping fuel into the engine. Per their advice I replaced the injectors, plugs, plug wires, distributor cap/rotor, & ignition coil, and it still wouldn’t idle.

We then read the OBD and it said that there was an open circuit in the TPS sensor, so we replaced the connector and it still wouldn’t idle. When I took the TPS sensor out to replace, the screws were broken off inside the screw hole- but the strange thing is that the car still won’t idle or stay alive without me pumping the gas, and I don't believe you need a mounted tps to do either, as long as the arm is in the right place on the sensor.

I feel like we are one part or adjustment away from this thing running solid but need some advice from someone who knows the model better, because google has led me down multiple rabbit holes. Any suggestions on what to look at?

 

You said they checked fuel pressure. Should be 54-55 PSI minimum.with 60 PSI the standard Might be looking at a new fuel pump here. I mean it's a 1989 model, and its gonna quit one day.

 

Chevy did a pressure test and confirmed that there was solid pressure. That was ruled out, unfortunately.

 

Thats a bummer when the dealership cant even figure it out. Still working on this matter. Q: can you see the spray pattern from the TBI injectors?

If its not fuel then it has to be ignition or electrical. Hoping your ECM is okay, Those arent cheap.

Is everything else clean? MAF, Air-cleaner, PCV valve, fuel filter? Any chance something like water is in the gasoline?

Any way it might be a vacuum leak or a bad EGR valve? Is it getting a good spark? (i know you replaced the cap and rotor)

Trying to rule these out as much as possible.

 

89 shouldnt have a MAF and fuel pressure should be max of 12 min of 9.

Troubleshooting sensors and how to test

a faulty or poor connection for C.T.S. would dump too much fuel. even a poor ground will mess up the signals

 

The 1989 did have a MAF sensor Irish_alley:

ACDELCO 2133205 {#19106672, 2134662, 88864353} Professional

My company used to own an 1989 K-1500 with a 5.7 liter, so I know I am accurate.I am a stickler about them, even though its not likely the
issue here.

I made the mistake of putting a K&N oiled air-filter on my 1998 K-1500. Big mistake and I was lucky that a good cleaning of the MAF brought it back
to life. Now it's AC Delco only air-filters

Something else is going on withjustintuah's K-3500, I just want to cover all the bases to find out what is wrong.

 

Tbi's don't have a MAF, they have a MAP, very different parts. Fuel pressure is 12-15 .

 

I know what a manifold absolute pressure sensor (MAP sensor) is and how it operates.Burnhedge. That said I admit that I was QUITE mistaken about the MAF sensor,on the 1989 Chevrolet model pickups, which used a TBI, injection unit, not a carburetor The spider style fuel injection system, which came out in late 1995-1996 with the (SFI) or spider style fuel injection system and, not the TBI, had the MAF sensor. as well as the MAP sensor. Please forgive my mistake and my apologies are extended to all involved in this matter..I am just a man who makes mistakes occasionally like all humans do..

That said I hope that we can still help this man out on his 1989 K-3500's issue with his Chevrolet pickup.

 

water under the bridge, lets fix this truck. we all make mistakes, OCH knew what he was talking about as the part numbers he posted are for the MAP he just called it the wrong name.

 

Justintuah - I’m not clear on the status of your problem after you replaced the TPS sensor. Are you saying you still have to “pump the gas pedal” to keep it running? Or is it just not idling well and you have to move throttle off idle to keep it running?