Problems Under Hard Acceleration

[gt1009]

I have a 90 Jimmy with the TBI 350. Truck has 296k miles on it, but I'm not sure if it's the original engine or what. When I accelerate anything above 1/4 throttle, the engine starts to cough and seems like it might be backfiring or something. Took it to a shop and they told me that the valve springs were weak and that was causing it. However, they also told me that nobody makes a rear window motor for the truck either, so I'm curious to see how much those guys actually knew. Does anyone have any other ideas? The truck will be accelerating fine, then cut out and make a loud noise, which will continue about twice per second until I back off the gas a little bit. It is not speed or gear related, but simple about how much throttle I give it.

 

[Z71paramedic]

I'd start by checking fuel pressure. A tune up (cap/rotor/wires/plugs) might help as well, but it sounds like a fuel issue to me. Possibly a pump/injector problem.

Does it only do it under load or if you just rev it up too?

 

[4xcrazy]

Fuel pressure..

 

[gt1009]

The issue only appears under load as far as I can tell, but I also don't rev it too hard. Changed fuel filter when it started a couple months ago and that didn't help. Should I go about getting a new injector along with a general tune up (cap, rotors, plugs), or should I try to get the fuel pressure tested somewhere?

 

[Z71paramedic]

Definitely test it. Don't want to throw $$$ at it if it's not an issue. More than likely it's a pump problem, but it very well could be an ignition issue. I'd pull the cap and look at it inside. My 93 did this one time and it was only a year since my last tune up. I was pulling my hair out by the time I pulled the cap and it looked like hell in there. $35 worth of parts later and no more runability problem I doubt the injectors are the issue, but it's possible too, but I'd start with the pressure test first and go from there. I think most auto parts stores will rent you a fuel system pressure tester

 

[diesel4me]

Knock Sensor?...might not be adjusting the timing correctly,causing that noise (pinging?)........could be spark being lost under a load too,the cap & rotor are good places to start looking,and the plug wires and plugs...weak spark will die out under heavy acceleration...fuel pressure too,as suggested....coil could be cracked or failing inside too...

 

[4xcrazy]

Only reason I said fuel pressure, is he decsribed exactly what mine did, unfortunately, while i was 400 miles from home in San Diego... Replaced a few parts that kept throwing codes, nothing fixed it.

Coughing, sputtering, serious lack of power, backfire through the intake when you try to force it to go, drove all the way back to Phoenix in 3rd gear because the engine wouldn't produce enough power to get it up to full speed and into overdrive.

Stupid thing would sit and idle fine, just under load was the problem.

Finally just got fed up and replaced the fuel pump, fixed the problem,,,, until the next go around with something else.