350 tbi problem???

[JOHN MEADOWS]

I just got a 87 custom 4x4 with a 350 tbi. The problem i found when you start it on a cold start it wants to surge to the point that it will idle up and down til it almost dies and then back up. After it warms up it seems to run a little better but you can still hear the surge. While the truck it appears to have power as it should. While at idle , it seems to run very rich. Since having the truck i have put on coolant temp sensor, iac , fuel filter, and rebuilt the throttle body. Nothing has helped it. Id like to keep it like the truck came, but im to the point of saying heck with it and putting a carb on it ( but really dont want to).

While doing this , I havent found a oxygen sensor on the exhaust and i believe i found the plug for it but it doesn't have one there. I have also noticed near the bottom of the front of the motor what i believe is a crank postion sensor that has nothing plugged into it. Did these trucks even have that on an 87? I have checked the codes and nothing dealing with oxygen sensor was showing. SO if someone thinks they can help me with this issue i would greatly appreciate it. Also would like to say that I'm no professional mechanic so bare with me please .

 

[JOHN MEADOWS]

I forgot to mention that i have checked the vaccum lines with carb cleaner and didnt find a leak.

 

[4WDKC]

Yes it should have an o2, should be in the driverside manifold. You state you replaced the IAC but did you do the calibration/self learn procedure for it? To properly diagnose a TBI you need a scanner or DIY cable connected to a laptop to see what the ECM is seeing and hearing. Without either of those your are wasting money throwing parts at it and its like trying to diagnose a carb issue while deaf and blind.

 

[JOHN MEADOWS]

Im not sure if my manifolds are the right ones for it but i dont even see a place for the o2 sensor on these. i haven't done the calibration yet due to not having a scanner so i can see my rpm to adjust the idle if needed. Im trying to located a scanner right now to do it. If this was the correct motor would it have a crank sensor on it? Because this one has it and no wires going to it?

 

[4WDKC]

Im not sure if my manifolds are the right ones for it but i dont even see a place for the o2 sensor on these. i haven't done the calibration yet due to not having a scanner so i can see my rpm to adjust the idle if needed. Im trying to located a scanner right now to do it. If this was the correct motor would it have a crank sensor on it? Because this one has it and no wires going to it?

get a paper clip bend it into the shape of a U, insert the ends into the upper right to slots on the OBD connector under the dash. Turn truck on but do not start, wait 10 seconds disconnect IAC, turn truck off, remove paper clip, reconnect IAC. Start turck, you may have to hold gas pedal for a few seconds while it adjusts. no scanner required.

 

[JOHN MEADOWS]

I will try that this afternoon and see if it works. Any idea on the crank sensor?

 

[1987 GMC Jimmy]

No crankshaft position sensor. It sounds like you’re talking about the knock sensor, which also needs to be plugged in. I’d like to see a picture just to be sure, though.

 

[JOHN MEADOWS]

Ill take a picture this afternoon

 

[JOHN MEADOWS]

Ok i got home and did the calibration on IAC . Even after that it would still surge. I will post a pic of the surge and maybe you can hear what I'm taking about. WELL I tried to upload video and it said error??

 

[JOHN MEADOWS]

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[JOHN MEADOWS]

Above is the sensor that I don't know what is nor have any wiring that goes to it

 

[4WDKC]

looks like a knock sensor

 

[1987 GMC Jimmy]

Yep.

 

[JOHN MEADOWS]

Anyone have any pics of the wiring from sensor and where it leads to?

 

[1987 GMC Jimmy]

It’s a blue wire that goes to the ESC sensor, which is going to be on the passenger side of the intake by the MAP sensor and EGR solenoid.

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