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Discussion Starter #41
Just a shot in the dark, plug in a CPS not installed (in your hand) and see how it runs.
Should trigger some codes also.
Toss the noise filter.
As a follow up. I plugged in the old ACDelco CPS and the result was long crank time, as expected & no change to the idle. So I am still leaning on a 5V reference issue at circuit 416 or a ground issue in circuit 452 of the crank sensor. These tests will have to wait and I have transmissions to build. I have an ACDelco CPS coming and it says it is 7 days away. I will try that first, because everyone is so adamant about the the use of the ACDelco parts. I used to be that way too, but in my line of work with transmissions. I have had a lot of bad out of the box ACDelco parts over the last few years. I even made a post on a bad OPS right out of the box that we bought for this truck.
 

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ACDelco part still have some DOA but at least they are built to spec at least for OPS.

I saw a post which was saved in my subscribed thread but gone after update.
In there, a member actually contacted the aftermarket company.
He got a spec that actually a lot less than the spec for ACDelco.

Another thing to keep in mind, ACDelco seems to have different tier of parts: Professional and OEM.
The Professional seems to be their lower end part with pricing of sometimes half than that of OEM.
This does not exist with OPS, though. I only see the same part no. D1808A (IIRC) so far, although that may change.
 

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Parts quality has gone down for sure.
 

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The Hall Effect sensor must produce a square waveform of 5 volt amplitude and the switch “off” down to zero voltage, it’s necessary to use a lab scope to diagnose Hall Effect sensors. If the waveform doesn’t pull down to near-zero voltage, the PCM may not be able to “read” the signal from the Hall Effect sensor. I suspect the offending sensor may not be pulling down to zero.
Since everything is speculation guessing the sensor is bad is just a wild guess. Maybe one day someone will verify this is the case with an oscilloscope.
Some sensor will read a perfect 5 volts but will not drop to zero. So one that goes to 5 volts and returns to say 2 volts will appear to be working fine but the computer just can't recognise the pulse that just happened. That's my guess as to what's happening. Might not have anything to do with this idle problem but gives some insight to aftermarket junk.
 

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Here is the thread about OPS:

The FAQ have a very excellent explanation on OPS.
 

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Discussion Starter #46
As a follow up to where I left off.

I had used the gremlin remover and found that the engine would idle smooth for a few seconds and then the injectors would start to clatter. I could replace the connectors to all sensors except the CPS and the idle was smooth. When I would reconnect the CPS it would idle ruff. disconnect it and idle is smooth. We decided it was a faulty CPS. The CPS had already been replaced by the previous owner. Because of time I replaced that one with a BWD (next day availability) and got the same results. It was recommended to replace the BWD with a genuine ACDelco so I had to wait 7 days to get it and find time to install. I finally got to change it yesterday. I got the same results; ruff idle or big cam feel. 3 entirely different sensors with the same results. At this point I am convinced it is not the CPS.
The IAT, CPS, MAP and Boost sensor share a ground at terminal D6 of the PCM. This terminal is grounded by the PCM. The CPS, MAP and Boost sensor share a 5V reference signal at terminal C10. The IAT is a 2wire sensor that does not use a 5V reference. All 4 have different 12V signals. This is where I’m heading. I will be looking at voltage drops to all 4 sensor’s and their respective signal wire, ground path or reference.
 

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Discussion Starter #47
So far I have come up with nothing out of range. The map, boost and IAT function correctly. They all have the 5.04V reference. They all have a shared ground at the computer and I get less than .5V voltage drop at every connection all the way to the computer. I am unable to test the wave form on the CPS.

I have read some post's on the injection pump/optical sensor. Some have stated that a surge at idle is too much fuel. They also stated that an optical bump causes a surge. NO, I have not touched the optical sensor. I have unplugged it, and it will not start.
I hooked my scan tool up yesterday, looking for a way to see the CPS on the scope portion of the tool. the whole time I sat at idle it surges at a high idle around 900-1100. It gets to be a less frequent surge and then it runs up to 2000. It flat lines at that until the key is turned off. It will restart immediatly and go back to the high idle surge for a few moments and run up to 2000 again. If we disconnect the crank sensor it idles smooth (just takes a long time to start) for a bit then injectors start to clatter..
  1. could the resister be incorrect for this application? we are using a #5, which is basically neutral or "0" on Stanadyne's scale of resisters.
  2. Could a dirty (it did sit for 3 years, the injector pump was off for 2) optical sensor cause to much fuel to be delivered at idle? If it can, how would you clean it?
  3. Could the optical sensor have come loose?
@DieselPro, @Glagulator, @quadstar87
I hope these pros I mentioned here can give me a little direction. Thank you in advance for your time. I'm trying not to be a parts changer, but I am new to diesels. It's much harder to fix something that you don't fully understand. I have been reading, researching & learning. Thanks to this forum.
 

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I am not an expert but I know the PMD resistor will NOT cause it.
As it is, the resistor is only read once in a blue moon well some say every 30 starts, some every 50 starts so there is nobody really knows.

From what I have read in the past, if the truck cannot hold the idle steady, it is either bad IP or at least bad PMD (there were a batch of PMD that caused surging before it went bad).
I am not sure what part of the IP specifically is bad that cause the surging, some say the armature or something like that.

DieselPro probably can give you a better suggestions.
 

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Thanks once again DieselPro for your expertise.



I see OKDually answered the SRTA?



That is to how I checked the CTS the first time and deemed it OK for use. Because we have spent so many $ so far another $25 doesn't matter. I replaced it and got the same results.
I read through the gremlin remover and unplugged everything except the OPS.
1) We got it started and it idles smooth as glass that way!!!
2) We plugged every thing back in and the idle surge is back.
3) We unplugged everything and it idles smooth again.
4) I decided to unplug every thing keeping the crank sensor (Short crank time) and it idles rough again.
5) plugged every thing in leaving the crank sensor unplugged and it idles smooth.

I have never seen a crank sensor make a motor run ruff.

As a gas guy the computer needs the crank sensor for the RPM signal. Gas will run with out a Cam sensor, but have extended crank times to find #1. I was taught 3 engine revolutions if both work, 10 engine revolutions if cam sensor is dead and no start if crank sensor is dead.
The 6.5L must use the optical sensor for the main signal and the crank sensor as a backup??? Is this why the longer crank times without the crank sensor? It fires right up with the crank sensor plugged in... to me that says the crank sensor is good. :confuzeld
The RPM signal that you see on the dash comes off the alternator.
 

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Discussion Starter #50
The RPM signal that you see on the dash comes off the alternator.
Yes I understand that the dash gauge RPM comes from the alternator.
The statement you used was as a reference to gas engines and my understanding of them. What is the CPS's purpose in the 6.5L? I was trying to get an idea of purpose of the CPS if not used for RPM's
when looking at DTC 19 "crankshaft position reference error"
Circuit description:
"The crankshaft position sensor is a magnetic induction type senor that monitors crankshaft position and speed."
speed=RPM or MPH
A Tech 1 scan tool shows 0 miss-count at idle, from that I have to assume it is good. The wave form signal should be square, but I do not have a way to see that wave form.
 

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Recently I have purchased quite a few parts from Rock Auto and a lot of them where AC Delco.... Hate to say it but all of them came from China... So I am no longer going to promote AC Delco as in the past. Perhaps you can find an old school oscilloscope to to read the wave form.. Starting to think it's your IP but sure would be nice to see the wave form first. From what i have read the CPS wave sometimes fails to go all the way to zero and the computer misreads the info. It must go to zero and then back up to 5 volts. Wonder if you could check the air gap on the sensor with the clay method? wonder if you could shim it out for grins and giggles.
 

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Discussion Starter #52
I am not an expert but I know the PMD resistor will NOT cause it.
As it is, the resistor is only read once in a blue moon well some say every 30 starts, some every 50 starts so there is nobody really knows.

From what I have read in the past, if the truck cannot hold the idle steady, it is either bad IP or at least bad PMD (there were a batch of PMD that caused surging before it went bad).
I am not sure what part of the IP specifically is bad that cause the surging, some say the armature or something like that.

DieselPro probably can give you a better suggestions.
For starters we have not been able to drive this truck as a daily yet. I don't really believe that the resister is at fault, but If the resister is way to adjust the optical sensor timing from -4 to +4. The issue started after some ignition cycles and we didn't count how many cycles it has been. I was throwing out the possibilty that after 30-50 cycles, it looked at the resister and didn't like what is saw. Then the PCM decided that it would add fuel, hence causing the surge/high idle.
The PMD has been changed. We bought a new engine harness, PMD and IP/PMD harness from Quadstar. It had a bad terminal at CK339 of the PMD harness causing it to die at times.
My son and I have also tried 1 other new and 1 used PMD from a friends truck that run's flawlessly. We have also put the PMD on a Heat sink at the plenum as opposed to behind the bumper. We even tried it at the PMD harness itself (no ext.). The truck idles smooth when using Dieselpro's gremlin eliminator at least till the injectors start to clatter from no CPS signal.
So I ask: For what purpose is the CPS to the PCM? I know the scanner sees a miss-count, that has to be less than 8 per cam reference pulse at idle or it sets a code 19. At that time the PCM defaults to back up fuel, fast idle and poor performance. I know injector timing is done through the (fuel distributor) IP. What else could cause back up fuel if no code 19 exists? I'm assuming that my surge and high idle are from too much fuel at idle. How else would I adjust this if not the PMD resister or IP timing? Every one states that I should start with the IP FSS in a upright or plumb position. That"s were it is and it will not idle properly. It has also been stated to fix the idle issue before moving on to "Time Set" and TDCO.
The IP was a new pump from GM about 55K ago. it was also off the truck and in the floor board with a reciept from St. Louis injection service for testing the pump and given an AOK.
I don't want to just throw an IP at it for $700-$900, when I know it idles fine with the CPS unhooked. My son also found video of this idling fine before. People were making fun of his excessive blow-by that went away after changing the CDR. so I believe that something is causing this issue. Even the guy that owned it before us said it ran fine until he ran it out of fuel. that's what sarted this whole deal...
 

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Discussion Starter #53
Recently I have purchased quite a few parts from Rock Auto and a lot of them where AC Delco.... Hate to say it but all of them came from China... So I am no longer going to promote AC Delco as in the past. Perhaps you can find an old school oscilloscope to to read the wave form.. Starting to think it's your IP but sure would be nice to see the wave form first. From what i have read the CPS wave sometimes fails to go all the way to zero and the computer misreads the info. It must go to zero and then back up to 5 volts. Wonder if you could check the air gap on the sensor with the clay method? wonder if you could shim it out for grins and giggles.
that's not a bad idea.. shimming the CPS. I think I'll go see if the shim from a 4.3L/5.7L will fit the ACDelco CPS I took out.
My OTC Genisys Touch has a scope. Do you think that might do? I think I have already tried to see it with it and it was a no go. I know most scan tools are a digital interpretation of a real time osilliscope.
Do you think a dirty optical sensor could cause this? How bout a dirty sensor ring?
The IP was a new pump from GM about 55K ago. it was also off the truck and in the floor board with a reciept from St. Louis injection service for testing the pump and given an AOK.
I don't want to just throw an IP at it for $700-$900, when I know it idles fine with the CPS unhooked. My son also found video of this idling fine before. People were making fun of his excessive blow-by that went away after changing the CDR. so I believe that something is causing this issue. Even the guy that owned it before us said it ran fine until he ran it out of fuel. that's what sarted this whole deal...
 

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Discussion Starter #54
I have not tried shimming the CPS. My son has started driving this to work. 6 miles each way ans he says It is getting better. It will idle good around 600 if put into gear sometimes. Sometimes it will idle normal in park or neutral.
I asked previously if too much fuel is the idle issue. Now my concern seems to be just the opposite, too little fuel.
Can anyone tell what the fuel rate shoukd be at an idle?
I found a document that shows it should be 8-11mm3. I see it as 0-4mm3 with a tech 1 scan tool.
Has anyone scanned there truck and looked at idle fuel?
I took a video of mine and it won't let me upload it.
 

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I took a video of mine and it won't let me upload it.
Uploading the video to Youtube, then copying the video link from the address bar and pasting it here in the forum works the best

(y)
 
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Discussion Starter #56
After all the testing and parts swapping it is a general consensus that we have broken armature in this 5068 IP. So my son is saving his $$ for a different pump. I believe we are going to send it off to have it looked at tested, confirmed as bad and rebuilt...
 

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Discussion Starter #57
Many thanks to all those that did give us things to look at and all the tech that was supplied. I was trying to not just replace parts all willy/nilly and actually trying to find the root cause to this issue. We were told that it was a broken armature of some sort inside the IP.
As an update to this. We replaced the injector pump today. My son picked up a 5521 Quadstar pump and traded a some parts to another guy for a 94-95 5521 chip. This truck is now running flawlessly. Idles smooth as glass, accelerates smooth, the transmission even shifts better.
I did ask earlier in the post about the 0-4 mm3 fuel at idle that the old pump had. I watched fuel at idle and just off idle it would ramp up to a decent fuel rate, but would never go over 60mm3 fuel delivery, even at full throttle. The truck felt lean to me, a lifetime gas guy. crisp throttle, high lopey idle and sensitive throttle. everything except the sensitive throttle screamed lean...
After the pump change we have a steady 12-13mm3 fuel at idle just like the book states it should be. Fuel delivery is up throughout the entire RPM range compared to the old IP. Under full throttle I saw a max of 79mm3.
Thanks again to @DieselPro, @Glagulator, @quadstar87
 
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