P1689 and no-start

[CCOLLAR]

TDR folks,



I've been having a peculiar issue for the past month and thought someone out there might be able to shed some light.



Here is the issue: when temps are below 40 F (not very often here the SF Bay Area!), and I go to start the truck up in the morning, the check engine light may come on, and the P1689 code - "no communication between ECM & Injector Pump Module" - is set. In some instances, the truck won't start. During one of the no-starts, I opened the #1 injector line to see if any fuel at all was being delivered to the cylinder, and there was none.



After several tries and some time (30 minutes or so) will catch and start. Otherwise, it will start right up. This only seems to happen in the morning on first start-up, though. The really strange thing is there is some correlation between the angle I park the truck on (slight incline with front on the down side) and the truck not starting.



The truck runs fine otherwise -- no mid-range rpm miss or hesitation, and no WOT miss or hesitation.



Originally I thought it might be the PM3 I installed over 1 year ago, but I have removed that and still experience the problem. I check lift pump pressure often and it has always been OK.



The truck: '99 manual trans with 70K miles.



Any help would be appreciated!



Craig

 

[Evan A. Beck]

Check the plugs on the ECM and on the back of the injection pump. The only way you can see this code is if there is a break in the connection between the ECM & VP44. Also, check all the ground paths for the ECM. Pay special attention to unplugging the connector on the back of the pump, and reinstalling it properly. Check for any bent or broken pins too. Also, if you used a scotch-lock to connect the PM3, make sure the wire you tapped onto is not damaged from the scotch-lock. I have seen this problem before... Keep us posted.

 

[GDouglas]

I have also had some brief occurences with the P1689 code. My experiences have been within a minute of initial startup; I start the engine, let oil pressure come up and it might hiccup and/or shut off all together within about 30 seconds with the check engine light for the P1689 code. On each of the instances, I cleared the code and started the engine again. I wiggled the pump connector and it's harness and the engine ran fine. I once had to clear the code 3 times and restart the engine before I got out of the plant parking lot, but it showed itself again about 10 miles down the road on the same ignition cycle that I left the plant on. Again, I cleared the code and wiggled the harness and pump connector with no luck on re-creating the glitch. I had a hunch it might have something to do with the DDTTM, so I disconnected it for a week and had no problems at all. I plugged it back in and ran fine for a couple of weeks and it happened agian just after startup. Cleared the code and drove a few miles and when I passed a vehicle, it only felt that I only had the stock hp available. Right after passing the vehicle, the check engine light came on for the P1689 code. I got home, cleared the code again, and checked for loose pins at the MAP and CAN-BUS connectors. They looked OK so I just sprayed some WD-40 into the connections before hooking them back up and I haven't had a problem for 2 months now. After running trouble free for 2 months now, I think there may have been a marginal connection to my DD box from either the MAP or to the CAN-BUS.



I will let everyone know if my P1689 ever shows up in the future.

 

[CCOLLAR]

Update

Thanks for the tips. I thought I'd give an update to those who are interested:



I have come to the tentative conclusion that this no-start situation is directly related to the temperature, regardless of the P-code. After much troubleshooting, it is clear that this isn't a random event. If the outside temp is at or below 40F, and the truck has sat long enough so that the internal temps are at ambiant temp. , then the truck won't start. After 7 or so tries, the truck will start right up.



Assuming this is true, then it would seem the problem could be either of two things: 1) a temperature sensor is giving faulty readings to the ECM, and the ECM is setting the error code and not signaling the FPCM with a start message; or 2) some logic in the ECM is hosed and is responding incorrectly to the sensor readings, and is not signalling the FPCM with a start message. (I originally thought it might be a faulty Fuel System Relay, so I replaced it, but that didn't help).



The questions I have then is this: Aside from the IAT sensor, what other temperature sensors are there? Is there a temp sensor inside the FPCM? Would a faulty IAT reading have enough "authority" to cause the ECM to send a no-start message, or not send a start message? For instance, if I remove the IAT, would that prevent the engine for starting, or would it just run crappy (I guess there is only one way to find out!).



Thanks again for the tips. If anybody has any other suggestions, please let me know!



Craig

 

[Michael Hughes]

There is a tempature sensor under one of the batteries.