What happened to my truck?!?!?

[4blaXzer4]

Once my 91 TBI warms up it sputters/bucks/pops when any load is put on it.
History: Truck ran absolutley awesome until approx. 3 weeks ago. On my way home from work my heater core started leaking inside and gave me a "buck" every once in a while. No big deal. Changed out core and while I was at it, changed out 160 deg. therostat plugs and brakes. Went for test drive and it started to sputter when given load. Thought maybe I had bad gas,so in went some dry gas and some Lucas. Over the couple of days it got worse. I then changed out cap/rotor, air cleaner, fuel filter. No help. My friends had me convinced it was a fuel pump, so I changed that. Drives much better, but still sputters under load. Since then I've swapped out EGR valve, checked resistance of coolant sensorand plug wires (good), replaced termostat with new 195deg. and replaced only broken vac line I could find. Used my chilton man. to check voltages at MAP sensor and they are all jacked up, but I fear that it may have an underlying cause. Like I said this only happens when engine warms up, runs great when cold. ANY SUGGESTIONS? HELP IS MUCH APPRECIATED!

 

[gauder]

Did you change the fool filter too?

 

[resurrected_jimmy]

you gotta let us know what the situation is now....... I'm going with gauder FUEL FILTER

 

[TrcksR4ME]

If the MAP sensor voltage is not right, then perhaps its the MAP sensor thats at fault. The MAP sensor is the single most important sensor when it comes to TBI.

 

[tch777]

My 1991 acted very similar when my coil went bad. Only ran good at full throttle and the rest of the time it was bucking and chugging.

Not sure if that is your problem but maybe????

 

[midnitewarya]

My Blazer used to do the same thing. It was always having problems with timing and would constantly bog down and stutter. It finally overheated so I replaced the temp sensor, distributor, coil, plugs and wires. After that, no problem. I would test the Ohms Resistance on the coil. Those things can cause alot of problems in the TBI. If it tests bad, thats your problem. If not, you got a cool excuse to get a performance distibutor!

Al

 

[diesel4me]

not sure ,but..

I'm not too familiar with TBI,but a pick up coil in the distributor (or a crank sensor if it has one instead) can do weird stuff like you described sometimes,and is temperature related often..runs good a short time,then acts up or craps out entirely after several minutes run time..

I've seen ignition modules do it too....the module controls spark AND the injectors,and one side can funtion normally,while the other side might work intermittently,or not at all at times..and it might not act up for days at a time too,just to make it more difficult to diagnose..you replace something,and think its cured--then a day later,it rears its ugly head again!

BTW--a 195 degree thermostat is the ONLY one any fuel injected motor should have,in fact ALL Chevy motors from 1968 and up came with a 195 thermostat,and its recommended for year round use..with a 160 degree,the sensors wont even send the proper voltage signals to the computer!.(might stay in the "cold" mode forever!)...unless its had one of those "high performance chips" added to the computer,they use a "cold" thermostat to fool the computer into delivering more fuel..

I'd use the 195 thermostat,you'll get better gas milage with the motor fully up to operating temperature..

 

[89K5guy]

Does it still have the catalytic converter?If so it could be causing this when it gets hot.It may be plugged.

 

[RustyParts]

I had a rocker arm one time that the push rod had worn a hole in, idled good but popped like hell when put under a load.

 

[4blaXzer4]

I appreciate all your replies. I have changed the fuel filter. Next I'll try the coil. Is there a value I'm looking for or just open or short? Also thought it may be the converter. If clogged would it run good cold? It still has the original "pancake" POS on it with 145K. As for the MAP, I'll probably change that too, although just from what I've read it doesn't seem that it is the fix. I'm thinking of trying winaldl.

Thanks for the info on the thermostat.

 

[theperfectgarage]

I would hate to be right on this one but the heater core part of the story bugs me.... did you maybe have a head gasket fail ? Could that add pressure to your cooling system and cause your heater core leak ? A longshot but I'm just thinking out loud. sure could explain the way she's running.