I took my '01 F350 in for the CPS recall the other day. Drove home from the dealer, overall several hundred miles, many stops/starts, ran fine, no problems. Strange, though on the trip - I noticed that once in a while the tach seemed to quit responding, just hung somewhere. No matter, got home OK and parked. Went out next day, no start - it has never run since. Cranks fine, plenty long enough to go, doesn't try to fire at all - no smoke, it is plugged in (warm engine), fuel bowl full and pressurized, all lights (wait to start, etc.) OK, full of oil, cranks long enough to indicate good oil pressure, tach wiggles while cranking. Tried putting old CPS sensor back in, all symptoms the same. What could it be?

 

It sounds like your CPS is good. It could be the IDM (injector drive module) which provide power to the injector solenoids to open them.

 

Just for the sake of it check the batteries. Maybe when you were trying to start it with the replacement CPS you ran them dowm. It may crank over but not have enough voltage left to fire the injectors. You need a minimum of 10.5 volts, even during cranking.

 

What provides the tach signal? I think that is a clue to the problem.

 

That would be the PCM, which uses the CPS to determine engine speed and position.

I was guessing a bad CPS or CPS connector/wiring. I looked at the manual and one of the symptom charts listed a symptom of
Incorrect tachometer indication:

Then things to check
Circuitry
Instrument clusterGenerator (diesel only)

I was surprised by the last one. I guess the first question at this point should be, do you see any smoke out of the tailpipe while cranking? Followed by, what voltage do you have while cranking?

 

Batteries are fully charged (recharged as needed). Checked glow plugs with ammeter, taking 80amps while energized before start, no smoke out the exhaust during cranking. The scenario seems to imply an electrical problem (computer has decided the engine isn't going to run). Fuel and fuel pump OK (drained and refilled filter bowl). Nothing was touched except the CPS changeout. I don't know if the strange tach indication was even real - maybe it was just a late night. I connected a scanner, there are no codes in the computer. Could there be a fuse that could cause this? I have heard about a fuel bowl heater problem. Also, I have heard about an injector driver wiring problem. Where is this module and how is it accessed?

 

How did you manage to keep your old sensor? Usually Ford will keep the old CPS when they do the recall.

No smoke means the injectors are not getting the signal to fire. A fuse is a possibility, but the locations vary among the year models. It's never a bad idea to check all your fuses with a test light to rule out the simple stuff.

The fuel bowl heater you've read about is on the same circuit as the IDM in the fuse panel, so when the heater shorts, the fuse blows and the truck won't start. To get around that, unplug the heater, then replace the fuse. The way to tell if you have a heater problem is there will be no wait to start light on the dash.

The wiring for the injector driver module (IDM) that throws a code & check engine light, and gives you a rough running (but will usually start) truck is under you're valve covers. The less common place to look for problems with this wiring is around the 42 pin connector. The connector is a square box with a bolt in the middle of it that sits on your drivers side valve cover. You may need to remove the intake tube off your filter to get good access to it. You can check to see if the wires coming out of the bottom of the box are chaffed and shorting out on the valve cover, or if the wires coming out of the back of the box are chaffed and shorting against a bracket. My experience with this has been the wait to start light will stay on and not go off when these wires are grounded.

Since you've been cranking the engine a lot, keep those batteries charged up. Weak batteries will spin the motor, but unless the IDM sees 10.5 volts while cranking, it won't command the injectors to fire.

Since the CPS is an odd animal, why don't you try putting the recall unit back in and see if the truck will start then. Just make sure you don't get a CPS from the auto parts stores. Those have been known to be bad out of the box, or die very quickly.

 

It's a sad story about my original (trouble free for me) CPS. Stupidly, I did not ask for it when I left the dealer. But when I got home a few days later and had the trouble, I called and discovered they had thrown mine out in the garbage. They have been trying to send me other known working ones from customer replacements, but didn't have any yet so sent one that was in a mechanic's tool box. I've got the wait to start light, so it isn't the fuel bowl heater problem.
I thought the IDM was supposed to be somewhere under the fender.
I can try putting the new CPS back in. What is so critical or fragile about them? Is there any trick to installing it correctly?

 

The IDM is located behind the drivers side wheel well. Follow the wire loom thats wrapped with red tape.

Nobody really knows why the CPS fails. Its a few simple electronic parts that die when they feel like it.

 

So the diagnostic that the tach moves when cranking is not definitive for a good CPS - it could still be bad?
There are 3 or 4 large wire connectors with a bolt through them going through the back of the driver's side wheel well. Does one of these go to the IDM?
I have read a lot of strange things about the CPS. Some engines run with the original black one, some run with the international blue one, and some run with the new gray one. Certain engines have trouble with some styles - none of the three seems trouble free.

 

Its hit and miss. The tach moves on some years and not on others. All three of those CPS's will allow the engine to run. The grey one was supposed to be the new trouble free version of the black one. The blue CPS is actually out of a DT466 motor (inline 6 used in many international trucks and busses).

I'm not sure if thats the IDM or the PCM you're looking at, but here's a bump back to the top of the page.

 

I received and installed a new CPS from Ford and installed it. Still no start. Checked all fuses (OK) and power distribution box. Had one 20A Maxi fuse blown (for radio), replaced, all checked OK, no start.
So have checked:
1. Batteries (fully charged)
2. CPS - swapped out, no change
3. All electrical fuses OK
4. Fuel filter, pump OK
5. HPOP - full of oil
6. Glow plugs flow 75A one side / 25A other side
7. Tried unplugging inj pr sensor on left head - no change
8. Cranks good, tach moves while cranking
What could it possibly be?

 

Any luck yet? I definitely sounds like your IDM took a dump.....

 

Nothing yet - I'm on the third new gray CPS. I wish there was a way to check what module may be at fault. The PCM, IDM, HPOP could be the culprits - I understand the only sensors that could prevent a start would be the CPS and ICP, and I already tried unplugging the ICP. If there were even qualitative checks to see if the IDM was trying to fire the injectors, or if the pressure existed at the HPOP, it could be narrowed down.

 

I rigged up a pressure gauge to check the HP oil rail and found I only got about 200psi while cranking. I heard that at least 600psi is needed to fire the injectors. Could the HPOP be bad? What could cause such a problem on a low mileage vehicle?