acceleration problem

[street legal humvees]

hello ! we just took in a m998 an 86 but had a recent gep swap looks like somebody rebuilt the injector pump as well we have limited knowledge of the trucks history / the truck starts and runs fine idles fine but under load w acceleration it iot bogs way down and will essentially not pick up acceleration after a few seconds with foot on accelerator it will rapidly pick up acceleration and appear to run ok once you back off pedal does same thing again
we drained fuel and changed the filter its getting good stream at the stopcock and we did crack most of injectors seems to be getting good fuel to the injectors.
tried to sorta do the old hand time with a 2 x 4 without any luck but don't have precision timing equip available . question is any thoughts? think timing may be culprit ? or any other ideas
second part of question while messing w this issue we noted we had i couple pull off injector pumps at the shop just not sure if they came off a 6.2 or 6.5l to be honest i know the 6.2l stanadyne is the db2 2829 4879 are there other brands or part numbers that were used ? is this the only 6.2l pump ie if ones in shop (am checking in am) are of a different number then they are 6.5l any help much appreciated

 

[papakb]

What trans is in your truck? If it's a 4L80 and the TCM isn't getting 12v or working properly you could be in limp mode.

 

[86humv]

6.2 can have : 4523, 4879, 6278.

 

[3jacks]

I had a similar issue, mine was a very small leak in fuel line under passenger side. Didn’t see a lot of fuel on ground when parked...but under acceleration it would lose power rapidly then surge. If you are seeing hard start as well...check all fuel lines. I found mine while someone was standing next to rig after start and some revving of the engine, fuel squirting everywhere...

 

[street legal humvees]

What trans is in your truck? If it's a 4L80 and the TCM isn't getting 12v or working properly you could be in limp mode.

sorry for delay , appreciate response ! its a 3 speed standard old humvee 3L80

 

[street legal humvees]

I had a similar issue, mine was a very small leak in fuel line under passenger side. Didn’t see a lot of fuel on ground when parked...but under acceleration it would lose power rapidly then surge. If you are seeing hard start as well...check all fuel lines. I found mine while someone was standing next to rig after start and some revving of the engine, fuel squirting everywhere...

will give it a look ! pretty sure we have a timing issue here !

 

[Milcommoguy]

Pretty hard to have a timing issue, unless IP pump shaft severed, timing chain skip a tooth or Samson bent the Injector lines into a pretzel.

I am not seeing timing as an issue, CAMO

 

[3jacks]

will give it a look ! pretty sure we have a timing issue here !

My MOTO: check and eliminate the easy stuff first. I had exact same symptoms you describe and it was a leak in fuel line. Those are things you should check over anyway. Let us know what the solution ends up being.