Another weird TBI problem!!

[southernspeed]

Has anyone had this. For the last year or so, when I start the truck from cold it will usually...but not always, sound like it is starting on 6 or 7 pots then after a few seconds it'll jump to 8, then back to 7 and back to eight again. This takes anything from 4 seconds to about 20. Then it runs fine and always when cold, never when it's run recently. It may not be dropping a cylinder or two but that's how it sounds. It's had plugs, leads ,cap, rotor arm and so on. I have not done a compression check as yet. Beginnning to wonder if it's something on the throttle body and to do with richening the mixture for starting. Maybe it sounds like it's only on 6 or 7 because it's not getting enough 'choke'??? /forums/images/graemlins/confused.gif Any body had the same?? /forums/images/graemlins/thumb.gif

 

[dyeager535]

Cold only problems I'd be going straight to the temperature sensor.

I know your location probably prohibits easy access to an OBD1 scanner, but if you've got a laptop, make the cable and use winALDL. Either way, I'd check that your temp sensor for the ECM is working correctly.

 

[TJS]

Sounds like a pick-up coil in the dist. is starting to show signs of needing replacement. Also check the magnets on the dist. shaft for cracking. If you do this replace the module as well and please use GM parts.

 

[southernspeed]

I've got the Winaldl programme and a LONG lead from my pc!
But as it only happens for a few seconds it hard to figure out what I'm looking at. Truth be known I need to figure out how to read the data properly and which are the sensor readings. I'll have to have another go with it and see. Thanks for the advice. /forums/images/graemlins/thumb.gif

 

[southernspeed]

Thanks, I'll check those. They've never been looked at since I bought the truck in '96 and it has got 160,000 + miles on it now. /forums/images/graemlins/thumb.gif

 

[dyeager535]

You don't even need the truck running to check the temp sender. Just turn the key to run, and you can see all the sensors at their "base" rate.

winaldl screenshots

I just jack in with my scanner if I need to do something quick, it has the right connector and is a lot smaller than a laptop, but not as much data of course.

 

[southernspeed]

Thanks for that. /forums/images/graemlins/thumb.gif

 

[dyeager535]

If it isn't clear where I was heading with my suggestion, with a cold engine, the ECM temp sensor should be very close to ambient air temperature. If it is reading 100*+ when the engine hasn't been run overnight, you know the sensor is bad.

 

[southernspeed]

Ok, know what you mean. If I survive this weekends enduro I'll have a go at it next week. Thanks. /forums/images/graemlins/thumb.gif

 

[southernspeed]

UPDATE!!It started running on 7 pots only so I pulled the plugs. Number 5 under the EGR valve was carboned up up inside it but the tip was clean. The metal body of the plug was a different colour to all the others and it STANK!! It did last time I changed them too, about 8K miles ago.The others are all fine. But the smell was an horrible burnt metal/plastic smell. Really weird. Do you think a small coolant leak in that cylinder could cause that? I lose about 2-3 inches out of the catch tank over the course of 1000 miles maybe at most. Always put it down to evaperation or small hose leaks etc. Any of this sound familiar to anyone? Thanks. /forums/images/graemlins/thumb.gif