bfrank79

the motor is in a 79 C10, and the harness was redone by speartech. I got running first about 2 weeks ago, it is straight headers and i did not have the O2 sensers hooked up, it would crank and isle just fine. Now i was gonna take it for the first test drive so I hooked up the O2's and just kind of rigged them with wire ties so they would stay just inside the opening of the headers. And now it will not idle. It pulses for a minute and dies, also the check engine light is flashing, Any ideas? do i just need to get the exhaust done and the sensors mounted correctly maybe?

Old Geezer

iTrader: (3)

Sensors hanging loose at the end of the headers will allow them to be hit w/ atmospheric air. They will report false readings, causing the problems you have.
Put the system on, make sure there are no leaks, install the sensors the way they should be, and retest...

Monte4ever

iTrader: (2)

What he said^^^^^^^^^

bozzhawg

X2 I bet the check engine or DL code will be P0171 and P174 or P0300 etc.... it is probably reading too much air or thinks its a lean condition, the ECM cannot compensate for the excessive air so once it maxes out of the fuel trim, it will go into safe mode...

Also when you start your car at first, the ECM runs open loop, not referencing the O2's, then after a period of idle, goes to closed loop referencing the O2's.....


Bozz

bfrank79

ok thanks, one more thing i forgot to ask about...during the first test drive i was going down the road and the thing just went crazy, no pedal response and barely idling. After some head scratching i noticed that somehow the positive post of my battery was touching the metal housing of my trans ecu, obviously it was shorting to ground and causing the problem. I have since relocated my ecu so that it wont happen again, but do you think i could have screwed the ecu?

bozzhawg

Hopefull you did not fry a circuit. A circuit that can easily get fried or damage is the one in the ECM that controls the throttle body on the DBW systems.... This circuit seems to be real sensitive.... its actually the plug that connects from the TB to the ECM... It works in a loop..... revolving from ground to power in a circular fashion. If this circuit is damaged what will happen will be no pedal response and not comunication between the pedal to ecm to TB.... Another way to check is, when you turn the key on but not the car, you should be able to hear the TB blade open and close or see it open and close to the position... If it does not do this, then your problem is prob a fried circuit that controls the TB.... Now this is only after you check all wires for continuity with the TB/pedal assembly....

The reason why I know this, because it happened to me before, and we spent 2 weeks chasing our tails trying to figure out WTF it was...

Bozz

bfrank79

ok, well the good thing is since then i have been able to rev it so i think thats still good. its just not idling, but i have not tried it with out the O2's again yet

Old Geezer

iTrader: (3)

Time to scan it, and run some data logs.....

bfrank79

how do i do that

bfrank79

ok, so i figured out that i fried my trans ECU, so what does it mean if the pedal does not respond sometimes? before i figured out that it was fried sometimes the pedal would not respond and i had to cut the truck off and back on and it would work fine. Could it just be the computer doing it?