88 Chevy 5.7L/TBI/700R4/Weird Problem

Posted in Ignition Systems

First: NO Check Engine Light. 150k original miles with the original engine/trans combo.

OK, as mentioned I have a 5.7L and I have a problem that is very hard to diagnose. Just today,I drove 2.5 miles without switching into overdrive ( 45mph zone), I jump on the freeway, get up to speed, shift into overdrive and then I cannot apply pressure to the gas pedal or I feel a lean misfire, hear popping through the TBI. I can actually feel it coming on as I get above 60 mph. But the kicker, Once I let off to go into coast mode and then go to reapply the throttle the problem is gone. That fast. Today, it happened just like mentioned above, I went 2 miles, got off the freeway and then grabbed a Coke. Jumped back into the truck, onto the freeway, did it once I shifted into overdrive going up a hill. Made it up the hill, crested said hill and then poof, gone. Not another problem remaining on the freeway for another 20 miles, stopping for about 45 minutes, getting back on the freeway for another 15 miles. This problem I DO NOT experience everyday. I can go months without it ever happening. I have only had it happen twice in one day, once. And it happened like mentioned above, drove over 50 miles and then happened in the middle of my drive going uphill. I use to be able to get it to do it going up a certain hill but, like I have said, once a month maybe. It has never happened twice in one week except for the twice in one day.

Parts already replaced. Ignition module, Coil, fuel pump and filter. Disconnected remote start for sh*ts and grins.
Parts installed aftermarket. Headers, Flow Master, Throttle body spacer.

I have over 20 years experience in the automotive repair industry and I am baffled at the moment. I am seriously leaning towards a PCM/PROM ?!?!?! Has anyone ever seen a oil sending unit for the fuel pump every cause an issue like this ??? I never have these symptoms below 60 MPH ( no tach, not sure of rpm’s). Lets hear from the Chevy gurus and see if someone could shed some light on this issue.


There are 4 Answers for "88 Chevy 5.7L/TBI/700R4/Weird Problem"

    1. Larry E says:

      How about the TBI it’s self. It might be starving the engine of fuel.

    2. adiabaticfire says:

      that sound like it might be the injector being plugged a little or low fuel pressure. id just dump in a bottle of good fuel system cleaner since thats cheap any ways and see if it goes away. it could be the ECU is confused because of your headers and throttle body spacer but i doubt it. if the fuel pump was weak it probably act up more often too. id just try fuel injector cleaner first. good luck.

    3. slipstream says:

      check timing chain for wear with timing light…check for slight wandering with timing light pointer…if there is it could be a combination problem with the timing control switch in the transmission which retard,s the timing in overdrive for fuel economy…that combination could create a problem when the timing chain slack,s due to acceleration/ deceleration. just a possibility that you could check…also check for vacuum leak at your throttle body spacer…vacuum rises up the & down the intake throat at different R.P.M,s & could create a lean condition that could cause the back fire condition you described…..good luck!

    4. brad h says:

      Gotta tell ya i have a 88 s-10 blazer 4×4 with the 4.3 tbi vortec and it does the same thing. i’m thinking it has something to do with the tbi system, only does it up steep hills or inclines and also turning around at fast speeds.I know carbs do that kinda stuff on steep hills (inclines) because of the gas flow, can’t put it into words but i’m sure you follow..as fuel injection does not have this problem..so i am assuming the tbi is part of the problem..not entirely sure but hope someones answer helps us both..