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ase_master327, Shop Owner
Category: Chevy
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Experience:  +15 years experience with Chevrolet. Bumper to bumper diagnosis & repair.
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1988 chevy 1500 v8 350 no power under load with timing retarded

Resolved Question:

1988 chevy 1500 v8 350 no power under load with timing retarded truck will run but idle is erratic or pulses replaced egr, o2 sensor, cap rotor, plugs and tested throttle position sensor and maf sensor. Can not find any vacuum leaks and motor sounds good as far as there is no engine noise like rattling or sloppy valves at acceleration. thought bad cam would produce some noise or possibly increased exhaust smoke.   Thanks, Troy
Submitted: 8 years ago.
Category: Chevy
Expert:  ase_master327 replied 8 years ago.
The timing is retarded?

That explains all the loss of power.

Bring it back uip to 0, and see if it helps correct the problem.. If not, then you will need a vacuum gauge for the next step.
Customer: replied 8 years ago.
I had to retard the timing just to get it to run. I disconnected the vacuum line to the MAP sensor and plugged the line and it idled normal and was able to advance timing back to zero. I replaced the map sensor and did not fix problem. Also tested fuel pressure, with ignition cycled it would go to 5 lbs and then bleed off, with truck started it carried 7.5lbs service manual say should be 9 to13 dont know if that is enough of a difference to matter. I am going to try driving it tonight with map sensor vacuum line plugged and timing at zero and see if it has any power. Any suggestions would be appreciated.
Thanks, Troy
P.S. The only error code logged was 44 saying o2 sensor was bad or that fuel mixture is to lean o2 sensor has been replaced.
Expert:  ase_master327 replied 8 years ago.
Well.. see there? You may have found the problem!! Either that, or there is a bad vacuum leak.. this could be stuck open EGR (but it wouldn't cause loss of power while accelerating).

It is the fuel pressure. Yes, even 1 PSI lower then the specification is too low, and will cause the lean condition that your 02 sensor is picking up. It takes that much pressure to push past the injectors.

It will most likely be the regulator or pump, if there are no leaks... So pinch off the return line that comes off the throttle body, and see if the pressure rises, if it does, then you have a bad regulator (torn diaphragm).. If it doesn't rise, then there is a problem with either the pump, or a leak (which could even be inside the tank).

Another thing to look into is the fuel filter, before condemning the pump. It could just be clogged completely up. The filters on these systems are super fine, and catch everything... That makes it easier for them to clog up than any other filter, for most any other system. On my old TBI 350 truck (personal vehicle), I had to change that filter every 2-3 months, because it would clog up that quick.
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