Chevy & GMC Vans

yes kings your right , we figured that out last night with a good diagram we finaly got our hands on . but thanx for trying to help .

Have I missed something or has no one mentioned "Throttle Position Sensor"? It could be a bad ECU.

Any chance if the motor jumped time it would cause these symptoms ???? i didn't consider it cuz of how good it runs in park . I mean theres not much left to consider . the electronics have all been replaced or checked , the fuel system was checked , he even rebilt the TBI with new injectors today & it still falls flat on its face in drive .

wheres that pull your hair out smiley when you need it ????

Wish I could help you out Dan...I am pretty much clueless unless it's basic engine maintenance.

You mentioned you had checked all the wires so this may be a moot point but I'll post it anyway.
I ran across this on false code 42's.
http://www.troublecodes.net/articles/gm ... td42.shtml

Try disconnecting both ECM connectors. Measure resistance on the white wire between the 4 pole connector at the distributor and the ECM, make sure you have low resistance between the two ends and high or infinte between it and ground.

Also once you have over 400 RPM the EST circuit should be a varing voltage. If the EST line is shorted to ground then the ECM will not be recieving a signal from the Ing module in the dizzy. Thus no EST control and inproper spark timing will result. Also check the knock sensor voltage, if it is open or shorted you will get a code 42. Check continuity of the knock sensor wire too.

That's a good article on the EST circuit. I wouldn't have bothered posting if I had checked that first.

ditto on the jumped timing, how many miles on this van? Disconnect the brown timing wire (for setting initial timing) and use a timing light to watch your timing marks. Disconnecting the wire will keep the EST from advancing and retarding timing. Watch the your timing mark while varing engine RPM and see if it jumps around. this can indicate a loose chain.

You brought up one other thought that's been bouncing around my brain - the knock sensor. It effects timing advance, but I didn't post it because I didn't think it would throw a false code 42. From everything skippy has checked it really seems that there has to be short to ground somewhere.

I'm going by memory, but I believe you can use a 3.5k resistor in place of it to determine it's at fault too.

Disconnecting the wire will keep the EST from advancing and retarding timing. Watch the your timing mark while varing engine RPM and see if it jumps around. this can indicate a loose chain.

when the brown wire was pulled the rpms were all over the place . so the next step is that we're pulling the timing chain cover to see what condition the chain & gears are in.

will let ya know how it turns out .

Dan,
You can pull the dist cap and number one spark plug.Put your finger over the spark plug hole and bump it over until you get number one at TDC.Check the timing mark so it is at -0- while number one is at TDC.Check the dist and it should be at number 1 post on the dist.If not and you haven't have the dist out then go for the timing chain and gear set.Just one tooth off will show up at the dist timing.To help locate TDC on number one you can pull the valve cover that side number one is on and watch the intake rocker open and then close.Once the intake rocker just closes that should be TDC on number one with it at -0- on the timing mark.Again the rotor for the dist should be dead on number one post.

before we took the cover off , at TDC the timing mark was at 14degrees advanced .took the cover off and there was about an inch of play in the chain LOL . i think we found the problem . saturday we'll put a new chain & gears on , put it back together & HOPE for the best . i'll let ya know how we made out .

keep your fingers crossed for us . Thanx

How is this coming Dan?

still not put back together yet , waiting on my cousin to make sure everythings kosher before it goes back together & the weathers not cooperating either .

I really can't believe this is happening !!!!! put the new timing chain & gears in , guess what ???? no friggin difference !!!! still runs the same way !!!!! we're stumped , i don't know what else it could possibly be . does anybody know how to test a TPS )throttle position sensor ) its the only thing left that i can think of . or like someone else suggested , maybe the trannys holding it back , doubt it but ......

it showed a code 42 again today too after running it for awhile , i don't know !!!! ](*,) ](*,) ](*,) ](*,) ](*,) ](*,)