Stalling w/ codes....Need Advice???

[TrboDzl Tahoe]

I've got a 96' Tahoe 6.5L with 145K. Two weeks ago I had a hard start followed by a "service engine" light. After a short drive, the light went out and I felt better. The next day I had my first stall, again with the "service engine" light. For the last 2 weeks I've had 5 stalls(4 at low speeds or just after stopping, 1 around 25mph) all with "service engine" light and then the light goes off. The light stays on anywhere from 20 minutes of driving up to being on for 2 days. It restarts just fine. After some suggestions from a few local diesel guys, this last saturday I changed the fuel filter and the Oil Pressure Sending Unit. The next morning.... ANOTHER stall and the engine light. I stopped by my local AutoZone and got a free scan. Here are the 2 codes I got...
- PO251 Injection Pump Metering Control A
- PO370 Timing Reference High Rs. Signal A Malfunction
FYI The lift pump was replaced at 104K. I've been reading about the FSD module and how that can cause stalling, but are there ever warning lights and computer codes that go along with that??? Anyone ever come across these 2 codes at the same time??? If you have any suggestions where to go from here, please let me know. Thanks for your time,
Nick

[ucdavis]

Both codes are related to the "optical sensor" on top of IP; both can be thrown by air in the fuel, or trash in the fuel (happens most if run out of fuel).
Here's an opus from a previous post on the first:
Code 0251 or 18 Post:
0251 is Injection Pump Cam System circuit. That is black gizmo ("Optical Sensor") @ top of IP. Same as code 18 on 94/95 rigs.
The gizmo reads rotating disc inside IP to tell PCM where in cam rotation pump is. PCM matches readings against crankshaft position sensor readings to assure appropriate timing of engine controls.
You can get this code if you run out of fuel (get air in IP), or run low & are "performing hard acceleration or turining maneuvers," have poor connections on IP or PCM or wires between the two have rubbed to where you get leakage of signal, or have broken wire inside insulation. PCM will have stored Freeze Frame and Failure records for tech to read w/Tech2 or equal scanner.
If intermittent, it will clear MIL light after 3 consecutive trips w/out the fault.
First check all connections & wiring for shorts or non-contacting condition. If everything in engine box looks OK:
Sensor has 2 wires if I remember; you should have 5 volts +/- 0.2, and 50mA @ the hot wire w/key on-engine off, and good ground to the other. If you have a 10 meg-ohm multimeter (don't do these checks if you don't) w/Hz scale, look for 57-63 Hz on brown-wire-w/white-stripe @ terminal A4 @ PCM w/engine running @ 900 rpm (or factor the Hz up/down proportianately to your rpm (idle of 450= 1/2 the Hz, 600=2/3, etc.). If the voltage is high it will probably be 12.6V and you have short to battery voltage & need to find it; if low, you have short to ground or open/partially open circuit & need to find interruption.
If gizmo is bad, you can replace it yourself if you pay mucho attention to cleanliness. On removal, you will be opening IP & will contaminate it if dirt or ?? falls in. Clean off top of pump & all around 'operating area' first (actually first find a Stanadyne dealer & get a new sensor & O-ring) then remove the torx screws, lid, circlip, slip sensor upper piece out of lid, remove big torx screw on lower sensor piece and carefully remove lower sensor from thin metal ring that rides in sensor-slot. Install new sensor in reverse order of the above. Activate lift pump to purge air from IP (w/engine off) & let run for 30 minutes or so. Key off & let rest for a while, then start up.
If you do this, post your findings & success. And I almost forgot, if you have less than 120K miles, forget the whole thing & let the GM dealer handle it under the IP extended warranty which is way better than this messing around. Also, the dealer has a scanner that will do some additional tests B4 replacing anything.
And you might check fuel filter; I have theory this code can come from contaminated fuel in IP; the holes the sensor reads are tiny & any blockage could cause a misread hole.

Code 0370 is error reading pulses on the disc & PCM matches reading to theoretically correct reading, so same air or trash in fuel could obscure the sensor's proper function, wiring/connectors could be trouble, or sensor could be fubar.
@ 145K, you're a great candidate to buy a new sensor @ local Stanadyne dealer & replace it yourself once you eliminate fuel issues (alternative is have them do it or get a new IP).
Post results please.

[Lionel_213]

OK, I have experienced the same type of stalling, start/no start symptoms as TrboDzl Tahoe, WITH the same codes, PO251 & PO370. The codes only tripped the SES twice during my numerous stalls, etc. I did not feel like pulling the intake and wanted to get the PMD out of the engine valley anyway so I got a cooler, new PMD and one of Kennedys' 40" extensions. I completed the job yesterday and, knock wood, have not had the problem again. I'm hoping the codes were tripped by the sudden loss of fuel commands from the "then Pump Mounted" Driver. I'm thinking about adding a thermosatically controlled fan to the cooling fins. Any body knowwho has something like that.
Best to all, Lionel

[Lionel_213]

I forgot, mine is a 1996 C-2500 extended cab, 6.5 TD

[Lionel_213]

Well, its been more than a week and almost a thousand miles and my problem appears to be fixed. Thanks to you guys!!!

[Lionel_213]

It also appears to have fixed my stumbling problems at @ 1800 RPMs.