No power at 2800 RPM and up

Chad_Kelsoe · August 4, 2015

I have a 2000 F-650 with the 7.3 diesel. I've done a ton of work on this thing within the last year. Injectors, exhaust manifold, up-pipes, turbo, HPOP leaks, etc. They brought it in with the complaint of missing when pulling a hill with a load( it's a dump truck by the way). I've road tested it, it pulls ok till around 2800 RPM, then just flatlines. Watching data logger I can't find anything abnormal except MFDES and VFDES start dropping around 2750 RPM. Once RPMs drop, they both then increase unit RPMs get up around 2750, then drop again. MGP stays around 15 psi, and my mechanical fuel pressure gauge shows 55-75 psi under load( it has the mechanical pump on the engine). The intake restriction gauge shows no signs of a clogged air filter, and filter looks visually good. Based on scan data, it looks like the PCM is limiting RPM. But I can't find anything in workshop manual or PC/ED that states this? Anybody got an idea if these are goverened? It use to have a super chip plugged into the PCM, but I removed it last time is was in. It was giving the typical issues with a loose chip with 7.3 PCMs.

jimmy57 · August 4, 2015

I thought 7.3 in MD sevice were governed

at 2800.

8WA Sman · August 5, 2015

Watch the waste gate pid. Did you try running it with the ICP disconnected? Also check map sensor for being accurate with regulated shop air. Make sure it has the correct calibration loaded in the PCM. Also if it had a chip hanging on the PCM circuit board check for cracks in the PCB.

Chad_Kelsoe · August 5, 2015

Wastegate is controlled straight off the turbo on the 650 trucks. I have not tried running it with ICP disconnected, but watching data logger ICP it seems to match desired and IPR stays around 30-35% at WOT, 9-10% at idle. It builds 16PSI on MGP pid, and map matches baro at KOEO. PCM is at the latest calibration already. It's ran fine(to me) since I removed the chip at the first of the year. This truck was a basket case when I got it last winter. Wouldn't start, injectors were all weak. Alternator was junk, exhaust manifold bolts were broke off. Then after those repairs, it starting intermittently dying and no starts. Found some bent pins in the central junction box, and it got a junction box and gem module. It was still giving me issues, that's when I found the SuperChip loose in back of PCM. The turbo was leaking where the exhaust housing bolts to the center housing and causing low boost, and fittings on the HPOP were leaking. Those just got replaced, and it runs great up to about 2800 RPM, then I see the PCM start messing with the VFDES and MFDES Pids and it's making me think that the PCM is governing the speed since it's a Medium Duty Truck. But I can't find it in PTS or OBDII Theory, Ford mainly speaks of the 7.3 in the F-Series Pickup Truck. And to my knowledge, this is the only local 650 that has a 7.3 along with the 7-speed manual trans. All the others have either CAT's or Cummins in them.

Chad_Kelsoe · August 5, 2015

Oh forgot to add it only revs to 2800 with trans in neutral with no load on the engine.

Keith Browning · August 5, 2015

The high idle spec on the medium 7.3L is lower than the light duty application. While the engine is RATED @ 2300 RPM the engine speed is governed to 2850 for automatic transmissions and 2750 for manual transmissions. It may also be helpful to know that these trucks in 2000 were speed governed to 90 MPH.

While checking boost it is normal to see readings begin leveling off after 2500 RPM.

lmorris · August 5, 2015

It's been so long since I looked at a 7.3L, but is there an RPM desired PID you could look at to verify it's being governed?

8WA Sman · August 6, 2015

The ECT isn't getting over 225 by any chance?

Chad_Kelsoe · August 7, 2015

Not that I know of. IDS datalogger only shows a pid for EOT, and it stays around 180ish. I've decided to ship this as is and see how it goes. I've informed the customer based on information from Keith that engine speed is governed. Most likely the chip in the PCM increased engine speed and now that I have it removed the customer thinks it's missing when the PCM governs the RPM, as it does have a miss feel to it.