SpeedySteve

1992 chev Van w/refurbished CarQuest 305 engine : After installing the engine I now have a back fire in the TBI when you mat the throttle and let off quickly, I have checked every thing I can think of , Vaccum good , EGR good, Injectors good , TPS good , replaced EST because that was the code I recieved last (43) Fuel Pressure check good, when you advance the timing it helps some but will not clear it out completely. My next option is to change the ECM ( Engine Control Module) has anyone ever ran across this problem?

SABL

Hi SpeedySteve,

First off, congrats on replacing a van engine!! No fun!!

The easiest check would be with the ignition system. Make sure the plugs have the proper gap and all spark plug wires are in good shape.

The only other thing I can think of is the timing being one tooth "off".... mistakes do happen even in rebuilt engines.

OK...another thought. How is the exhaust system? Is the Cat clogged?

Something is leaving hot gasses in the cylinder and when the intake valve opens, it ignites the incoming fuel.

Only thoughts on the matter...perhaps someone else can be more specific.

Best of luck,
SABL

SpeedySteve

Thanks for the Reply Sabl , Plugs, Wires , Dist, Ignition module , EST,ECM, EGR, IAC,,and TPS have all been replaced chasing this issue and the Cat is clean as well .........It drives great under normal driving, IT HAS ME PULLING MY HAIR OUT! Thanks tho!

SpeedySteve

BUDFAN8

i think SABL is correct in the 1 tooth off theroy. advanceing the timing would pull it closer to on time. the only way fire can get into the intake is from a valve not being closed all the way. weather it be an exhaust valve not closeing and the heat combusting when the intake valve opens or an intake valve not closeing and letting fire through when the plug hits.

pull out the #1 plug and get the piston TDC (top dead center) you may need something to stick in the plug hole so you can see when it stops moving up (straws are good to use because the wont harm the engine if they get in a bind) when you get #1 TDC remove the distributor cap and the rotor should be pointed directly at the #1 piston (this is if you have the round dist cap with the plug wires in a circle) if its the one with 5 leads on one side 4 on the other standing in front of the motor looking back at the firewall it should be in the 7-8 o'clock position.

if all that stuff checks out good you can pressure test the #1 cylinder and it should hold if the cam is in the correct position. if no way of pressure testing you may need to remove the timing cover and make sure the cam mark is in the correct position.

Bud.

SpeedySteve

Thanks BudMan , Yea I have checked and double checked TDC , I've been told If a valve is bent and not closing there would be a skip or miss constantly, Just like a dead cylinder. Thats not the case here,The Van road test great , with the exception of the mat it test. I guess I'll go back to work tomorrow and pull the Timing cover back off.

Thanks for the info

mack1

Hi Steve,

Looks like the general thinking is the 'one tooth off' cyndrome. I would suspect that also. If that's not it, take the distributor cap off and clean it good with alcohol. Sometimes there is a carbon track that you can't even see that will cross feed the spark to the wrong plug.

The cam position sensor should be right there near the timing belt. Look it over good while you are under the car. Clean it up and make sure the electric connector is firmly attached.

It would be nice if you had a friend with a vehicle just like yours where you could switch out the ECM/PCM long enough to rule that thing out.

Wishing you the best,
Mack1