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ate lug
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Discussion Starter · #1 ·
Ok, i need some ideas here.



First up, truck specs:

96 F250. Auto, 141k miles. Reman PCM from cardone ~2 months old, TDE7 calibration. Baby Swamps, Swamps IDM, Swamps tunes (chip currently removed). The usual intake/exhaust combo. Lots of new parts in the last 8 months (MAP, ICP, EBPS, fuel pump, fuel heater, glow plugs, GPR, UVC harnesses, VC gaskets, VSS, CPS). FPR & IPR were serviced in September.

Ok, symptoms.
The truck had big issues which led to me checking alot of stuff back in september, ended up finding corrosion in the PCM, which is why it got replaced. That immediately fixed the truck, however it ran like crap when cold (would act like a failing CPS). Once it warmed up, the truck ran fine. However, as of this past saturday, the truck runs like hell all the time. it acts like a bad CPS, and it finally threw P0340 on saturday, and again yesterday when i stopped by the local garage so we could pull codes on the truck (i do not have a scanner). It died in their parking lot. No tach movement, and CPS DTCs. Cleared em and put my new spare motorcraft CPS in, and nothing. Threw P0340 again and wouldnt start. Swapped both back & forth but got nothing. Got a ride home, and went to the dealer to get a brand new Motorcraft CPS. Swapped this one in (#3) and nothing. Threw P0340 again. Went home as i was soaked from working in the rain.
This morning i went back, and it still wouldnt start. Unplugged the PCM, ohmed the wires for the CPS, everything in the wiring seemd fine. I have 5v where im supposed to, the ground is good, and i get 12v down the signal wire from the PCM, when the key is on.
Put it all back together with my old CPS (#1) and it started up, but only ran for about a minute before stalling out. Threw P0340 yet again. i never got it started again. Had it towed home, and took the wiring harness apart. I inspected & ohmed the wires from the CPS to the square connecter on the fenderwell, they all look good. I ohmed the 3 from the square conencter to the PCM connecter and again everything looks fine. So whats wrong with this thing?! Is my Cardone PCM no good? Is my camshaft bad and none of my CPSs can target it? At this point i dont know what to do, short of replacing wires 'just because', even though i cant find anything wrong with them.



Short version: Truck didnt run, replaced PCM. Truck ran like crap when cold, then like crap all the time, now it wont start. Constant CPS codes with multiple different CPSs. All wires ohm good.
 

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ate lug
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Discussion Starter · #2 ·
One more thing i forgot. This truck has always had a shim behind the CPS, so when nothing worked i tried a CPS w/o the shim, but it didnt change anything. I did not notice any marks on any of CPSs indicating the camshaft hit any of them.

other useful info:
Yes i get my Wait To Start light. I checked every fuse, theyre all good. The fuel heater is not currently hooked up, instead its wrapped in tape, to eliminate a bad heater.
 

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Just a WAG, but maybe try to peer into the hole where the CPS goes, using an inspection mirror and a well-placed light? Maybe there's something blocking its "interaction" with the reluctor (or whatever) on the camshaft. :shrug:
 

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ate lug
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186 Posts
Discussion Starter · #6 ·
Any idea what i should be looking for? i mean, i can see the camshaft gear, and i see the holes the sensor counts, but beyond that i dont see anything. There cant be anything blocking it.

I tripled checked my wiring this morning, cant find anything wrong at all. +12v, +5v, and a good ground. Even tried shaking the harness while watching the meter but nothing happens. At this point, im thinking i need to get a hold of a scanner or AE or something, so i can see if the CPS is sending a waveform back to the PCM or not.
 

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ate lug
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Discussion Starter · #7 ·
Ok, heres another curveball.


I have a CPS form Advance Auto. It that cheap BWD line they sell. It looks like the old black International CPS sensor. Its been laying around in my garage for about 6 months, because the truck doesnt run right when the sensor is installed. It would idle fine, but the throttle was choppy, almost as if it was sending back a bad waveform to the PCM. Anyways, i had removed that in favor of a Motorcraft CPS a couple days later (again, about 6 months ago), which cleared up the choppiness. I figured the sensor was a cheapy, and didnt work right, but kept it in case of emergency.

Just put it in, and bam it started. it has that same choppy throttle it always had, but it started. So, thats brings this to my attention, taken from Intellidog


No start at times; Intermittent stalling while driving during warm-up or when hot, usually restarts; Power "hitch" at cruise or under load; Possible DTC#'s P0340, P0341, P0344:
Cam Position (CMP) sensor.
The CMP sensor provides the PCM with cylinder ID and engine RPM. Sometimes hard to detect, even with a scan tool while monitoring the RPM signal. If the PCM does not receive a clear CMP signal, it won't signal the Injector Driver Module (IDM) to energize the injector solenoids.
If this symptom occurs, or if you find one or more of the above codes, check the wiring to the CMP for continuity--BOB pin 90 to CMP pin B; BOB pin 65 to CMP pin A; BOB pin 49 to CMP pin C. NOTE: A code P0344 may be set any time the engine is cranked for an excessive period of time. Early CMP sensors were @ 1.152" in length, and with the different materials--plastic sensor, aluminum timing cover, steel tone ring) the air gap would change drastically during engine warm-up. There were TSB's published for shimming the sensors 0.010" to cure these problems as well as the drastic repair of replacing the camshaft--something a Navistar tech assist rep recommended not doing even if excessive end play was verified. There have been two updates to the CMP. One to decrease the length to 1.142", and also to improve the internal circuitry for less "noise". The CMP designed for engines built after serial number 375549 have gold-plated terminals and cannot be substituted with those designed for previous engines.
94-96 CMP: F6TZ-12K073-A; original Navistar part suffix C-96, C-97; replaced by C-98; replaced by C-99
97 CMP: F7TZ-12K073-A; early suffix C-91; replaced by late suffex C-92; both replaced by C-93.
The suffex is stamped on the connector end of the CMP and can be used to identify the level of the part installed. Replace any CMP's with a suffex of C-96, 97, 91 if these symptoms are experienced. Lube the o-ring and connector with silicone dielectric grease when installing.
Specifially, this part
The CMP designed for engines built after serial number 375549 have gold-plated terminals and cannot be substituted with those designed for previous engines.
94-96 CMP: F6TZ-12K073-A; original Navistar part suffix C-96, C-97; replaced by C-98; replaced by C-99
97 CMP: F7TZ-12K073-A; early suffix C-91; replaced by late suffex C-92; both replaced by C-93.
The suffex is stamped on the connector end of the CMP and can be used to identify the level of the part installed. Replace any CMP's with a suffex of C-96, 97, 91 if these symptoms are experienced.


So this tells me thats there is two different CPSs, and they are not interchangeable. Can anyone confirm this? i thought they were all suposed to be interchangeable. the BWD sensor has the gold-plated terminals which according to that article indicate a later-model 7.3, whereas all the Motorcraft sensors have the typical silver terminals.

My serial # sticker is gone, and i cannot read the embossing near the oil filter, so i have no idea what my serial # is.
 

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The difference (as I understand it) is the '97 sensor and connector uses gold plated parts for less signal loss. If you interchange either part, the tin plating on one part rubs off on the gold plating and can create some corrosion, resulting in a loss of signal over time.
However, both CPS are electrically the same.
 

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So then its safe to say that i have 3 bad CPSs, two right out of the box?
That is not very likely. Take a good look at the connector, but it seems you have checked it out.

Since the PCM resides inside the cab, it would/should be difficult to corrode. The IDM is more susceptible to water damage.

Also, UVCH's seem to often be the culprit, but I don't believe the code you see would be related.
 

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ate lug
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Discussion Starter · #12 ·
I had the PCM out yesterday, it is 100%. As i would expect from a 3 month old unit. My IDM is fresh from Swamps (just got it ~2-3 months ago) so i cant believe that is bad, nor would i think it would cause a no-tach situation anyway. It has always thrown an IDM code since the day i put it in, but i was told thats because of the higher voltage.



Im thinking its a wiring issue. I removed the BWD CPS to measure the distance to the camshaft gear. Came up with ~1.160". Spun the crank and measured about 8 times, came up with roughly the same number. Subtract the CPS (all of them are ~1.142") and i get an airgap of ~.018". Now, ive always had a .020" shim in there, so that gets me an airgap of ~.038".
I tried all the Ford CPSs again, couldnt get it to start. I also could not get the BWD to start it if the shim was NOT in there, meaning to me that if its too close, it cant tell where the windows are. So i put the shim back in and it wouldnt start! But after playing with it for a second or two i got it running. So even though all my wires ohm out good im wondering if there isnt something goin on in the plug anyway causing a signal loss, or just a bad signal. I dont have the proper tool to take apart those style connectors, so i cant say if one of the terminals isnt broken inside the plug (the probes on my volt meter are larger than the pins on the CPS, so they could be making contact where the CPS is not). I shook, pulled, poked & prodded these wires with no change on my volt meter, so i cant believe its bad, but frequency based sensors are pretty sensitive. So anyways, i have a new pigtail on order, it will be in this afternoon.
I think i need to buy AE, it would be nice to be able to see if the sensors are sending a signal back or not, and if so, what it looks like.
 

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ate lug
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Discussion Starter · #13 · (Edited)
Sooo.....it might be fixed.

This is the new plug, Ford p/n# 7U2Z-14S411-SA.


As you can see, it is not exactly the same design as the old! It fits into the CPS much better than the old plug did. it fits a ton of different Ford vehicles, altho it claims its only for the 96-97 7.3s. It appears to have the gold terminals (which is why i figure it says 96-7), so im getting a late-model CPS on tuesday but in the mean time, all my regular CPSs seem to work just fine. I cant explain it, maybe the signal wire was frayed and it was sending back a wacky signal, i dunno, but i was running errands today and had zero problems with the truck, using a CPS that previously wouldnt start the truck.


eidt: fixed typo in p/n
 

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Thanks for posting that up! Another part number added to the list. Cheers!
 

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You did, cause I just tried to order mine.
 

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Im going through this problem right now bad.. been through 14 cps's, 4 different brands, each brand reacts differently than the other when the cps "fails" what im curious to is what is the correct part number for that cps pig tail? My phone wont allow me to pull up the image that has the proper part number on it
 
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