IP pump cam reference signal

[DA BIG ONE]

I have a question about IP pump cam reference signal "missed counts"?
I have 191 missed counts and need to know what this means?

[gmctd]

The CPS puts out 1 pulse per cylinder

The OS Cam Ref also puts out 1 pulse per cylinder

The OS Hi Res outputs 64 pulses per cylinder

Anytime one of those three sensors fails to send it's pulse, PCM will log the event in a designated counter, 1 count for each missed pulse.

IIRC, 8 missed pulses in a row, you get a DTC, which will clear if pulses resume - occasional missed pulses just accumulate.

Those cleared DTC's will store in History for later Diagnosis.

Missed pulses can cause fishbiting, hard-starting, etc.

Missed pulses can be caused by dirty fuel, curly fries, macnuggets, etc.

Also by failing connections, failing Optic Sensor.

Clear those, check later to see if more occur.

[kenisret]

the optical sensor provides a pump cam signal to the PCM by counting pulses on the sensor disc located in the inj. pump.The pump cam ref. pulse is one of the most important inputs by the PCM for timing and start of injection. DTC 18 will set when 8 cam ref. pulses are missed.
I am having this problem now and I have a code 18.I keep getting the code 18 every time I clear it so I am thinking I need to rep the inj. pump due to a bad optical sensor which can't be replaced by itself. I put on a new optical sensor harness but that didn't help.Possible causes for this problem as listed in service manual are:
1. bad optical sensor
2.bad sensor harness
3.bad PCM
4.faulty or open circuits

[kenisret]

I forgot to mention in my last post that when DTC 18 sets the sys will go into limp mode and perfoormance and economy will suffer.My truck is presently in limp mode and it seems to drive normally but it is extremely hard to start.I'm thinking I need a new inj. pump due to a bad optical sensor

[DA BIG ONE]

Just replaced IP, have no codes other than P1656 cause I run a turbomaster boost controller.....

Truck is running fine, starts easy too, have tdco @ -1.9

I'll check harness.

[gmctd]

They may be leftover from the previous pump - must be manually cleared.

Was that why you replaced the IP?

You can replace the OS in-frame, Ken - just need to be very clean about it.

[DA BIG ONE]

They may be leftover from the previous pump - must be manually cleared.
Was that why you replaced the IP?.

I had changed out IP because I got a DTC about a mechanical failure of cam in pump. How can I clear it manually, disconnect batteries, or? I did have batteries out when replacing IP, timing gears and chain out to a phaser setup.

[gmctd]

Takes a bi-di scanner, or maybe hold the acc pedal to the floor, turn on the Ign switch, release the pedal after 45 seconds, turn the Ign off.

[kenisret]

GMCTD
I was told by a reliable source that the OS can not be replaced as a separate item because it needs to be calibrated to the pump. Did I get some bad info.? Where can you buy a new one?

[DA BIG ONE]

GMCTD
I was told by a reliable source that the OS can not be replaced as a separate item because it needs to be calibrated to the pump. Did I get some bad info.? Where can you buy a new one?

http://www.mamut.com/homepages/Norwa...h/newsdet9.htm

[gmctd]

Some camrings are marked, some are not - if not, remember to scribe a line on the camring to the passenger-side of the OS before you remove it.

Install the replacement to that line, and you should be within a couple RCH's of correct timing

Also remember - the tone wheel, or encoder disk, is thinner than one of those anorexic super-models, so due caution is imperative.

'Nuther words - be careful...........................

[DA BIG ONE]

I'm stumped w/this one my carcode shows random engine miss too. I'll try another pump driver today, but this little hickup (miss) as I like to call it seems to have been w/truck since new... I'll dig into harness at EMC as have had some loose pins in the past.....

[gmctd]

You might try replacing the CPS and OS - both can give too many pulses, for which there is no DTC.

Symptoms range from hard-start to fishbiting.

Kill each injector at idle to see if it is an injector - PCM closely controls idle speed by varying the fuel rate, will log a Cylinder Balance DTC for any problem.