What happens if fuel density compensator stop pate is removed?

[Mark3395]

OK, I'm back down at Papabear's shop to resume recovery of my 109 van.

History: I picked the truck up at Warner Robbins and it was a pig. It labored to run about half speed.

Changed filters and assured fuel was flowing fine. Fine help from SS guys lead me to adjusting the Fuel Density Compensator. First, I bypassed the FDC. No improvement.

So consensus was to adjust the FDC for more energy. In so doing I discovered that the guide adjusting screw... the one with the two adjustment nuts on it... was broken. No spare so I had to improvise.

I first tried putting padding under the sheet metal cover to keep the screw pushed in. No help. I resorted to drastic measures... removing the moveable stop plate (see page 1-30 and others in TM 9-2910-226-34, Injector Pump).

WOW! Ran like a striped assed ape!

That concerned me. Too good to be true? I considered that too much energy delivered to the engine could damage it so I set out conservatively... and blew a head gasket in about 7 miles. The truck's been down here since.

Troy changed the head gaskets out and found that the heads were not properly torqued. He feels that was the root cause of the head gasket failure.

I drove the truck a few miles yesterday... with the FDC bypassed and the stop plate removed. Moves powerfully, but I'm concerned I've still got a fundamental part missing.

So the questions are:

1. Considering that the FDC is bypassed, what bad things happen with that stop plate removed?

2. Is it possible to use conservative driving techniques to avoid trouble?

3. Must I replace the IP with another with the stop plate in place?

4. Is it sensible to just replace the FDC with another one that's already adjusted... stop plate and all?

If it's safe to drive, I'll be able to go to the GA rally. If not I'll need to think about this and leave the 109 behind in favor of another truck.

Thanks much for your kind wisdom.

Mark

 

[M543A2]

We have fuel density locked out and fuel turned up. Driving sensibly with a boost gauge and a pyrometer installed will keep you out of trouble.
Regards Marti

 

[jwaller]

pyro gauge for sure.

 

[Mark3395]

I don't think I'll be able to get a pyro installed today... but I can get a digital IR thermometer and do a little driving and checking.

What temps am I looking for, and where? Turbo and exhaust manifolds?

The truck's temp didn't rise above 170-180 during my drive and idling yesterday, but it was a conservative drive. Might want to tow my SECM back N with me.

 

[cranetruck]

Even with the FDC bypassed, you'll need the stop plate.
Let me know if you need a replacement, I think I have one somewhere...

The EGT should not exceed 1,200°F.

 

[Mark3395]

Thanks Bjorn.

What happens if it's removed? Excessive RPMs?

I've got a take-off IP here... but shortage of time. Might have to make a separate trip.

Mark

 

[cranetruck]

The stop plate sets the max fuel delivery, I would have to look at the mechanism to see what happens when it's removed.

 

[Mark3395]

That was my understanding, but I don't know if just keeping your hoof out of the accellerator any more than required for usual speed is a useful workaround. I surely thank you for your review of the issue. The manual isn't very clear about the implications of the system. I'll look for the trouybleshooting guide to see what's there and try to make sense of it.

 

[Keith_J]

Definitely a pyro because any hill and you maintaining 55 MPH would probably put too much heat into the cylinders. Yeah, the turbo is a concern but the pistons are far more sensitive.

 

[m16ty]

I don't think I'll be able to get a pyro installed today... but I can get a digital IR thermometer and do a little driving and checking.

What temps am I looking for, and where? Turbo and exhaust manifolds?

The truck's temp didn't rise above 170-180 during my drive and idling yesterday, but it was a conservative drive. Might want to tow my SECM back N with me.

Using a IR thermometer won't work unless you can figure out a way to check it while going down the road. If you stop and check it by the time you get stopped and get out of the truck to check it it will have already have dropped several 100 degrees. EGT fluctuates alot more than coolant temps. You can be running 400 at the bottom of a hill and hit 1200 mid hill and dropped back down to 600 at the crest.

 

[Mark3395]

I'd thought about the hills, and think I can be conservative and downshift per usual rather than letting the engine pull me if it's running powerfully. In addition I can run slower... like 50.

I still haven't ciphered what the bottom line effect is... dumping more diesel into the engine I think.

Perhaps I could run with another fuel blend that would be more suited to the metering.

Or perhaps I should just bite the bullet and make an IP change part of the day's festivities.

Any thoughts?