Hey guy thanks for letting me join. My son and I inquired an 87 k5 350 with this. The truck is loading up on gas. We have a rebuilt this, new fuel pump. New cap rotor plugs. WE FOUND DISTRIBUTOR of by about 20° out advanced. Put it back to 0°. Two plug wires were crossed. Put everything back as should be. But it still loads up new tbi. Question, could the computer module be messing up? Could the wiring to injectors be wore out.( wiggled them and it seemed to level out but went right back to idling kind of rough)? Any suggestions would be appreciated. Thanks.

 

Could be a bad coolant temp sensor, MAP sensor, O2 sensor, or a few other things. Is the check engine light on? OBD1 won't have nearly the onboard diagnostic capability that OBD2 does, but it does have some.

BTW, nice rig. I have an '88, but it's not in nearly such good shape.

 

thanks Tom, no check light but also no oxygen sensor or map sensor either. They either eliminated them or the beast never had them don't know. Got it from so derlick that didn't know much about it. So should it have these sensors in 87? And could it be the issue, not giving computer the right info for the pulse for injectors?

 

I know some emission controls some years were only on California models, but I'm pretty sure yours should still have a MAP sensor and an O2 sensor. If the underhood decal is still there, it should tell you.

Basically, if the coolant temperature sensor circuit was open, it would "think" the temperature is -30 degrees and richen the mixture accordingly. Same with the MAP sensor thinking you were under heavy load all the time, and the O2 sensor reporting the mixture as always lean. You can check those values with a voltmeter, but a scanner makes it much easier.

 

Not sure if you can get any good data readouts from an 87. They are pre OBDII and possibly feature a GM ALDL plug.

As TomA said, the TBI is mostly susceptible to coolant temperature input and MAP. One issue found regularly on the old TBI engines is rotted vacuum lines.

As for these old trucks they usually have only one O2 sensor in front of the CAT. The ECU does not know if a CAT is there or not. If the O2 sensor is bad it simply does not go into "closed loop" (which means it's controlling according to the O2 sensor) but should run more or less fine. Lack of the O2 sensor would set a CEL (check engine light).

 

My '88 gives pretty good streaming data on my Monitor 2000 scanner. It's primitive compared to OBD2, but it's definitely helpful. I almost got rid of the thing years ago (bought it brand new in the 80s when it was state of the art), but then it came in handy when I got my '88, lol. I would recommend one if you have an OBD1 Chevy, since they're usually available on ebay for $20-30 now.