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11/98 cc drw 6spd under 2500rpm slight miss, long starts.

2K views 17 replies 3 participants last post by  Dirk 
#1 ·
My brother just bought this truck with 217K in good shape.
It has a hypertech chip/programer and came with a not-yet installed propane kit w/tank and remote fill.
Problems; truck takes 3-4 seconds to start hot or cold. Batteris and starter seem to be in excellent condition.... engine spins quickly durning cranking.

Under 2500rpms at idle or load engine feels like there is a slight miss. After 2500 the engine feels perfectly smooth and has great power. It does not feel like a dead cylinder as the miss is not that strong. seems to hesitate around 1250rpms on acceleration.

Stuff I've checked; air cleaner is a dreaded k&n. I pulled the intake tubes which were fairly clean as well as the turbo fins. fins actually looked perfect.
removed oil cap to check amount of blow-by... just steady light vapor. place hand over hole with no feeling of surging or pressure.
drained very slight amount of water from seperator. I have not replaced fuel filter but will be doing so today or tom.
The truck MIGHT smoke just a bit on cold startup but once warm doesn't smoke at all. There is very slight smoke on hard acceleration (hypertech set on stage 2).
The truck was purchased from a second owner who purchased it 2k ago from uncle. (2nd owner is rich and sold this truck because he bought a 4500.) afaik the ONLY major maint. was recharging ac system and replacing a couple injectors.

CEL works but is not on.

anyone have suggestions as to what might cause this "miss"?

I'm going to take the pressure reg out of the back of the hpop this afternoon if I can find an oring kit to service that.... maybe there is some debris in the small needle valve and its allowing oil to flow out and not build pressure until the engine cranks long enough to build pressure?

can the HPOP be weak and not build enough pressure at low rpms which might cause the engine to "miss"?

any help would be fantastic!!!! have a good day,

Adam
 
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#2 ·
Have someone do a contrib/balance test and check for codes. Do this before you pull the IPR. A good scanner should be able to watch the data stream and you can watch the ICP/IPR numbers. That will tell you if she is building enough oil pressure at start up.



 
#6 ·
So I called a shop and was referred to a guy who service's most of the PSD tow trucks in town. He said that all he had to do for a contrib/balance test was to hook it up to a scanner for $42.50. Does this sound like what test you are talking about being done? I have access to a full shop with scanners. I would just need to know what parameters I'm looking for specifically. I've scanned gassers but no diesels so I'm not sure on the HPOP pressures and all.

Thanks
Adam
 
#7 ·
If you have access to a scanner that has the ability to do a contrib/balance test, do it. It's a pass/fail test.

HPOP (IPR/ICP) pressures are different between trucks.

On your early 99 with a 15* hpop (assuming you still have AB injectors), at idle your ICP should be around 700-900psi, under load (40-60mph) around 2000psi, at WOT it should be 2500-3000psi.

Those are ballpark figures only.

As far as your starting, watch your ipr dutycycle.. you should see it rising as your cranking. Also, in the morning.. check the oil level in the HPOP reservoir. Should be around 1/2 inch from the top.

Change the fuel filter and check the fuel pressure.



 
#8 ·
how do i find out which Injectors the truck has?

I scanned the truck with a Modis scanner.

Injctrlpr(kpa) was 3300 at idle = about 480 psi

Seemed to build pressure quickly during cranking... spiked to 17,000kpa just as the engine fired.

The Balance test Failed the #8 injector showing a P0284 code. :(
Where should i go from here? Is it just best to replace it or can I clean it or run any other tests to make sure it's the injector and not something else?

THANKS AGAIN !!!
Adam
 
#11 ·
Being a 11/98 truck, I'm willing to bet you have AB injectors. You'll have to pull the valve cover to be sure.

How many times did you run the test? Was the engine hot? I've seen random contrib/balance failures at number 8 before.

As long as your compression is 400psi or better, I'd just replace the injector.
 
#16 ·
If you have AB injectors, you'll need to replace it with a AB.

If by some ODD chance you have AD's and you really want a AE, then go ahead, but I believe the programming is a bit different also.


Simple answer, replace it with what is there. If the cackle is bothering you, get a regulated fuel return setup.



 
#17 ·
Ok so here's what I did:

Took off drivers side valve cover. Verified that I have AB injectors. Started truck and noticed that #8 was spurting about 1/4 the amount of oil as the other 3 injectors. So I swapped injectors 2 and 8. O rings looked fine and cleaned off the injector nozzle with a brisle brush. Restarted truck: #2 was about 1/4 the amount as the other 3. #8 looked fine. (even after running the truck for a while with increasing the RPMS) I can get a new injector for $290 but the shop isn't open on weekends or I would have bought one today.

I'm definitely going to start doing some fuel mods. Anything to help quiet this baby down. Tanks mods, dual fuel pumps, oil x over tubes.... the work shall continue!
 
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