Engine/Transmission (1994 - 1998) No Throttle Response..........

[Greenleaf]

Hi Again guys.



I have a '97 12 valve with the P7100 (in a school bus) and it's acting up. It runs great NORMALLY with good power (100% OEM factory,etc. ) Fuel psi is 30 # plus, with a good load on the engine.



I have noticed that the engine will cut out (like it has no fuel) then it dies while driving. Sometimes it will also remain at WOT even when I pull my foot off the accelerator, then slowly lowers it'self and dies. Sometimes it will run fine and when I give it WOT there is NOTHING there. No throttle response at all.



Any ideas?



Could it be sucking air... ... ... ... ... ... . intermittently? It's an intermittent problem obviously.



Scott

 

[Joe G.]

You might check the throttle linkage lever where it bolts to the lever on the injection pump. If it's like mine, it will be attached with two screws, 8mm heads. I had one fall out once. The friction from the other screw still allowed it to work, but it had crazy symptoms similar to what you have.

 

[Greenleaf]

I have drained the fuel from the tank to check for sludge and water. Pulled the AFC from the injection pump to look at the internals and tripple checked all linkages for throttle and shut-down solenoid. The fuel filters are not new but they wouldn't show this type if problem. They are four months old.



The school is telling me they will opt to park the bus as opposed to replace the injection pump. We just don't have any money. I don't have time to R&R a pump anyhow.

 

[Bob4x4]

I had a case where the cut off solenoid was coming apart inernally... ... . some times work fine and others would not. Very intermitant. Coils were both fine



Bob

 

[Greenleaf]

I have performed more tests. The flow volume test is kinda dumb cause to crank the engine over for 30 seconds and measure volume is near impossible. By the time I hit 15 seconds the egine has slowed to half it's cranking speed and at 20 seconds the engine is turning too slowly to do much. This is with the battery charger set on "start" mode, 225 amps.



I have been driving it and come to the conclusion that it runs great under a heavy load but, when the load is suddenly removed, the enigine looses fuel, sputters and shuts down. Right out there on the road!! It will restart immediately and off I go once more.



Sometimes it has no throttle response at all.



Any more ideas.



Scott

 

[MLee]

Greenleaf;

Just read your problem, have you tried to disconnect the selinoid, electricly, and undue the selinoid linkage and MANUALLy turn on the fuel lever on the pump to see if the selinoid is the problem? seams like this would be one way to eliminate the devise to see if it is causing the cut out. Just a thought! How about a bad relay????????? the hold up juice has to come from someplace, A bad connection?

Marv.

 

[Greenleaf]

Thanks. I have been operating the engine with OUT the solenoid.



I spoke with a fellow @ Shied's Diesel and was told it's a plunger hanging up.



I can drive this thing with the engine cover removed. I set right next to the injection pump. When the pump acts up, sometimes it emits this loud ticking sound..... then the sound disapears. Then it's back. Sounds like the shut-down solenoid on/off/on off. Loud/fast pop. pop. pop. pop. pop. But, it isn't moving.



I connected a clear hose in place of the pump supply line and see no air bubbles. The pump ALWAYS has good fuel pressure. Even when it won't run right. I just pulled some fuel lines to perform a visual and no problems found. Changed the fuel filters again. Made no difference.



Scott









Scott

 

[bgilbert]

Sounds like its time to swap in a VE:-laf... sorry had to. . hope you get it figured out.

 

[Greenleaf]

Yeah. I got it figured out all right. I parked the thing. I have an entire bus fleet to care for and cannot continue to troubleshoot this thing for a third day.



Thanks for the tip about the VE. I'll do that when I need to downgrade a bus engine.

 

[Greenleaf]

FYI



I spoke with the driver and found that I wasn't the only one to experience the "No Throttle Response Symptoms"



It seems the pump has develpoed a mind of it's own and will set in the lot untill the school can conger up enough pennies to rub together.



I just had a fan belt break loose and take out the electric fan clutch ($773. 00) and a transmission burn up. Along with the usual "no head lamps/burned up heater motors etc. etc. " That was this week... ... ... ... ... ... 25 buses to care for and one bus mechanic.

 

[GRotman]

sounds like a plunger is haning up, which will cause the rack to not be able to return to the idle posistion. Time for a new pump.

 

[Greenleaf]

Yep. Looks like it. The O ring at the barrel/plunger must have leaked some fuel around the barrel and is sticking somewhat when the engine gets good and hot. . When it comes to transporting kids, you don't mess around with a bus that is questionable.

 

[Greenleaf]

FIXED



I just finished with an install of the rebuilt injection pump. The thing runs wonderfully. No more stuck throttle. The barrel and plunder assy on a cylinder was sticking. I'm surprised it occured at all as this engine is only at 80,000 and is all OEM in a school bus. One of them things I guess.



-S