6.0L Losing sync at lower rpm

Mekanik · May 29, 2008

We have a 2005 F250 with a 6.0l that came in and it wouldn't run. I'm not the tech working on it, I'm just trying to help. The truck will start if you give it throttle when cranking, but it stalls when the RPMs go below 700RPM. It loses FICM sync and then stalls. The IPR, FICM and I think FICM harness have been replaced along with the CMP and crank sensors. The PCM was swapped with a known good vehicle. The wiring for the CMP has been overlayed and the tech looked at the crank signal with an osciliscope and says that it is a good signal. We got the thing running and I wanted to do a power balance test and see what happens when we turn off the injector enhancement, but it wouldn't let us go into power balance or enen control the RPM. I asked about rust build up beetween the CMP and crank sensors and the block, but there wasn't any. This truck sounds like it has a biased ICP and it is very quiet when it is running, but we disconnected the ICP and ICP voltage stays constant. I'm thinking something with the cam or crank signal wheels. Any help would be appriceated.

mchan68 · May 29, 2008

What is your ICP volts at KOEO? Should be around 0.2 volts. How about your FICM voltage PIDs? Did you check for Vbatt at the FICM relay? Check for a harness rub through at the top of the shock on the driver side. HTH

OHNO60 · May 29, 2008

had same issue with an ambulance one time. Weird thing it was the egr valve stuck way open. Dont know why it didn't flag a egr dtc. was doing same exact thing. As a matter of fact the sync dropped just before it stalled also. Gave me a run thats for sure. Quiet as a gasoline engine too.

Bruce Amacker · May 29, 2008

We have a 2005 F250 with a 6.0l that came in and it wouldn't run. I'm not the tech working on it, I'm just trying to help. The truck will start if you give it throttle when cranking, but it stalls when the RPMs go below 700RPM. It loses FICM sync and then stalls.

To verify this, I'd graph out FICM SYNC and RPM (and a few others like ICPV), do a recording, and see which one drops out FIRST. This is really important!

The IPR, FICM and I think FICM harness have been replaced along with the CMP and crank sensors. The PCM was swapped with a known good vehicle. The wiring for the CMP has been overlayed and the tech looked at the crank signal with an osciliscope and says that it is a good signal.

There's more to it than "looks like a good signal". Compare voltages with the known good capture I have, as a low voltage output will cause your exact problem.

What pins are you tapped on? Pins 30 and 31 with the scope ground lead hooked on bat negative should give you the exact waveform I have. Make sure your initial "sweep" goes up on the CMP and down on the CKP. Make sure you have 14 CKP teeth from the top of the CMP wave to the beginning of the CKP identifier. Make sure your CMP voltage is near +1.5 to +4.3v and your CKP is near -2.4 to +6v. Check the RPM PID as a graph while it's running and see if it's erratic. Check end play in the crank. You can actually remove the CKP and slowly crank the engine while examining the CKP trigger wheel for damage. Change SYNC and FICM sync into a bar graph and check it for being erratic.

We got the thing running and I wanted to do a power balance test and see what happens when we turn off the injector enhancement, but it wouldn't let us go into power balance or enen control the RPM. I asked about rust build up beetween the CMP and crank sensors and the block, but there wasn't any. This truck sounds like it has a biased ICP and it is very quiet when it is running, but we disconnected the ICP and ICP voltage stays constant.

Huh? When the ICP is disconnected, the ICPV should go to zero in scan data.

I'm thinking something with the cam or crank signal wheels. Any help would be appriceated.

The CKP trigger wheel could be loose, and the CMP trigger PIN can also come loose, but it usually hits the CMP and makes a mark on it. Did the guy inspect the old components, or are they still hanging around?

I'd disconnect the alternator to see if excessive AC was causing problems.

Good Luck!

/forums/images/%%GRAEMLIN_URL%%/grin.gif

Mekanik · May 30, 2008

The ICP is reading .28v KOEO. When I said that it sounds like it has a biased ICP what I really mean is that is how it sounds. When I mentioned this to the tech he said, " I know, thats why I unplugged it. " So it was doing this with the ICP defaulted. That can be injector timing too by the way that it sounds. I checked the harness and it is rubbed through, but it is only the harness that goes back to either the trans or the transfer case and it was unplugged to see if the problem would go away with it unplugged. I asked about the FICM voltage pids and he says that they are all where they are supposed to be.

Stuck open EGR... That kind of makes sense. I'll mention that in the morning.

Bruce, I know what your thinking with the "good signal" statement. This guy has been using his "old school" osciliscope and I told him that I would like for him to make a recording with the CMP and crank sensor readings with IDS, so that we can compare to known good readings.

What I meant by ICP voltage stays constant is that it isn't erratic and dosen't drop like it would if it had a biased sensor. As far as the sensors, there was no damage to the CMP or the crank sensor.

Here is something wierd:

The FICM sync reads sync, no sync, sync, no sync when cranking and without touching the throttle. If there are only 3 injectors plugged in, FICM sync is ok, but if 4 or more injectors are plugged in then the FICM sync gets erratic. All the powers and grounds for the FICM have been load tested and the communication wires from the PCM to the FICM have also been load tested. The FICM has been replaced and a known good PCM plugged in.

jared_bortel · May 30, 2008

I've had them do the same thing with switching sync and FICM sync PIDs when crank tone wheels walked. You can check it somewhat using a screwdriver to attempt to wiggle it through the hole in the block for the crank sensor. Or just pull the oil pan and really get a good shot at it.

GregKneupper · May 31, 2008

i had one with this concern one time and it was a crank trigger wheel that had come loose. try doing a relative compression test and see if it pops up a cam/crank synchronization error code.

Tony302600 · June 2, 2008

i had one with this concern one time and it was a crank trigger wheel that had come loose. try doing a relative compression test and see if it pops up a cam/crank synchronization error code.

Mine was an engine harness causing that.

Mekanik · June 4, 2008

Thanks for all of the replies. Very good information. He hooked the osciliscope and looked at the ckp and cmp waveforms and the cmp looked really noisy and the voltage was much less than the one that Bruce posted. The tech finally fixed the truck by cleaning the block with a scoth-brite pad where the cmp is mounted to the block. I mentioned rust build up when he first started looking at this truck, but he swears that there was no rust. /forums/images/%%GRAEMLIN_URL%%/shrug.gif. The cmp waveform was much better after the truck was fixed and the voltage was a lot higher too.