BeardedWonder92

First off, new to the forum but have used its abundance of knowledge.

5 months ago i found a killer deal on a 89 pickup with 290k that was running but smoked. bought it as a project/ 2nd truck, drove it around for a couple of weeks to access the problems. performance sucked, had a rough bumpy idle and smoked and consumed oil and check engine light would come on and go off, (never got to check the codes before rebuild). So i figured first things first and after encouragement from superbleeder's rebuild thread I parked it in the shop for a couple months and gutted her. Sent the block to the machine shop, bored it .020 over, decked .008 off the head surface and turned the surfaces on the crank. It went back together with a laundry list of goodies, used engnbldr rebuild kit with new h2o pump, oil pump, timing kit. Also engnbldr's street RV head and 261 crawler cam. Sent all the injectors off to witchhunter for cleaning and they all checked out. From Lce: header, complete rocker assembly, adjustable cam gear and a few odds and ends including new fuel filter (important for later). Ted from engnbldr was extremely helpful in getting the cam degreed in. I timed the cam 2° advanced off the 110° centerline. Went through the recommended break in period and timed the ignition to 5° advanced correctly with te1 - e1 jumped and 12° not jumped. All and all when it was said and done, I had close to 3 grand in motor. First fire was a beautiful sight, fired right up and ran great.

After things got settled and 400 miles put on the motor the rough bumpy idle is still there. almost sounds like it is not firing randomly and it smells rich. I have codes 21 41 and 51, the tps was adjusted per fsm and was in spec. the tps sensor its self was a little draggy but did not get stuck through its range. i have read you can adjust the afm to lean up the mixture but i feel like that is a bandaid to my problem. Fuel pressure seems to be good, as i was priming it before i first fired it i forgot to tighten the cold start injector and fuel went shooting 4 ft out of the engine bay, fuel pressure, check. I have checked and sanded all 4 grounds and every thing seems to be good there. i have a suspicion its a short somewhere... somewhere.

what do yall think where should i start???

scope103

Do you know what those codes mean? Code 41 points right at a "draggy" TPS. But rather than feel it blind, put your multimeter on VTS and slowly open the throttle. The resistance should climb slowly and SMOOTHLY. If it's jumping around, your TPS is bad, and SHOULD throw 41.

Do you know what 21 means? Most likely cause is an open/short in the O2 sensor HEATER circuit. At your mileage an O2 sensor is a maintenance item, so I'd just replace it, but don't forget that your problem is in the CIRCUIT, not just the sensor. The wiring for the O2 sensor is in a hellish environment, and if you break a wire you'll get that code with a perfectly good sensor.

For code 51, just make sure the A/C is off, the transmission in in park (neutral), and the throttle is closed when you check for codes.
Yeah, you can, but it would only affect operation in "open loop." Which is not your problem. The O2 sensor controls the mixture after a few seconds, and then the setting of the VAF means nothing. You'll regret messing with the VAF.

Why? Shorts are always possible, but do you have symptoms that point to that?

BeardedWonder92

when adjusting the tps i didnt see spikes or drops in the meter but i will check agian.

all the criteria was meet for code 51 when i was pulling codes. which in my head points toward a short, i know very little about wiring so i could be completely wrong. but with 51 and the throttle mechanically closed, in conjunction with 41(tps/ tps circuit) makes me think a short or bad ground (maybe??) in that circuit which is falsely telling the computer that the throttle is open which throws the 51 and the short bad ground that caused the 41 is somehow all related to the o2 miss reading and throwing 21..... just a thought.

anywho i have my work cut out for me chasing the o2 wires and rechecking the tps

the efi electrical thing is alittle over my head so i appreciate the ideas.
thanks

Clifford1990

Where did you go to buy the O2 sensor? How did it hold up, also, last question, how was it to access the circuit?

BeardedWonder92

Haven't tackled the o2 yet. I put the multimeter back on the tps and it was in fact faulty. Got a new one on order and will post results and if i have to tear into the o2 circuit.