94 12v wont rev out

jupton

jupton

Horsepower lover
Joined
Aug 19, 2009
Messages
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Hey guys im working on this truck for a buddy of mine. 94 5spd 400k on it. Problem is at about 1800 rpm it starts to pop and backfire and wont rev past 2000 at all. Ive checked the timing its still at factory setting. Replaced all six injectors with another set that i know are good. Lift pump pressure sits at 20 psi at idle and does not drop. Set the valve lash and checked out the top end, everything seemed fine there. The truck starts right up and idles fine. At this point im thinking it may be an issue with the injection pump? Any ideas would be much appreciated.

Thanks, Josh
 
thats what i would think. when my pump took a dump it would rev up to 1800 and bog back down. wouldnt backfire or anything just wouldnt rev.
 
I checked the timing with the timing pins in the back of the timing gear housing and in the pump. Set the engine at TDC with the first pin and the one in the pump slipped right in. I assumed this was a good enough method or is it possible something in the pump could have changed?

I was thinking about gov springs too but it smokes and pops and carries on. I would have though the gov springs would be cutting the fuel to it and it would just not rev higher and not be smoking and stuff. Maybe im wrong here i dont know. I guess that will be my next thing is check out the gov springs.

Any more ides would be welcome, thanks
 
I'd prefer to check/verify the timing with true TDC and plunger lift... and set it beyond factory spec. Factory spec on early trucks had a TSB about white smoke, stumbling, and poor fuel mileage :eek:
 
jupton said:
I checked the timing with the timing pins in the back of the timing gear housing and in the pump. Set the engine at TDC with the first pin and the one in the pump slipped right in. I assumed this was a good enough method or is it possible something in the pump could have changed?


Any more ides would be welcome, thanks
Click to expand...


That just checked that it was set at whatever the pump was set at at one time.

Some pump shops set the pumps at 0
 
I just had a truck in shop that it would only rev to 2000 and would backfire and blow white smoke everything checked out and talk to my pump shop and it was the rack sticking in pump put a bottle of stanadyne fuel conditioner in it and it treat 60 gallons fill tank and dump whole bottle in. then drive and work throttle a bunch you may get lucky if not you will need a rebuild.
 
Ok thanks for the help guys. I will verify the timing with the plunger lift method. If that doesnt fix it looks like the pump might be coming off!
 
dont forget to make sure the over flow valve is good my 94 did the same thing and i put a new one in it and it well hit 4k no problem.
 
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