What did I miss?
I have a stumper on my hands and looking for direction. Towed in crank no start. RPM's on scan data. No fuel pressure on scan data and a P1233 Fuel Pump Driver Module offline code. I'm familiar with the FPDM case corroding and causing issues and half expected to see this here since I live in the salt belt. The FPDM on this van is on the frame rail right behind the fuel filter. There was no evidence that the case was compromised. I then unplug the connector (C3239)diag.net/file/f72l56g3n… to the FPDM to bypass it so that I can check the operation of the fuel pump. Jumping pins 4/5 and 2/3 at the FPDM connector give me direct power and ground to the pump. It buzzes so I am good with that for now (I didn't check the actual fuel pressure when it was bypassed nor did I voltage drop the wires from the connector to the fuel pump I did however check and confirm power and grounds at the connector once the van started diag.net/file/f1c7qmpvd…). I plug the FPDM harness back in so that I can check pins 1 and 3 that feed the modulated signal and driver command back to the PCM. I only have a two channel labscope. When I cycle the key I hear what sounds to me a slightly delayed fuel pump prime. I decide to crank it and it starts. I capture the event and proceed to cycle the engine on and off and it starts every time. I reluctantly take it on a test drive and there's a little hesitation an acceleration but it clears up and I can accelerate through it. Scan data shows good fuel rail pressures throughout. I get it back to the shop and start doing some brake torques in drive and reverse and I can see the signal break up. diag.net/file/f74gt2azy… Here I'm on Pin one at C3239 and the other lead is one the same wire at the PCM (pin 40).
I moved one lead to Pin 80 (yellow trace)to see the integrity of the PCM's ability to switch to ground. It looks solid during the stumble event.diag.net/file/f2gbdcgou…
I let the van idle for an hour to see if it would die out and it didn't. Idles smooth. I make the call to replace the FPDM. No dice. I have the same symptoms as before. That was Friday afternoon and I was going over service info again this weekend to see what I'm missing. Any insight would be great. I'm going to go over all my notes and retest my powers and grounds on Monday.
I have seen a few where the ground strap between the body and frame is broken or has high resistance. Some you just touch and they break. If I remember correctly its by the passenger side door. Good luck.
I just had an e van this week that would intermittently not start with the same conditions you are explaining. Ended up being the ground wire on the passenger side of the van (just about under the passenger front seat) between the body and the frame was broken. Fixed the ground wire and has been going strong for a week now.
Hi Martin: Does this beast have a voltage issue or was it caused by your testing? Guido
Hi Guido, I believe there to be a voltage issue. Can you elaborate on "caused by your testing?" Was there something I should have done differently. Not at all taking offense to that question. I just want clarification on your end. Maybe the fact that I disconnected the connector to test the fuel pump and "fixed" the problem|" when I plugged it back in only for the van to start? I knew when the…
Hi Martin: Looking at the Min & Max readings in your screenshots, the voltage is appears to be low, very low. Disconnecting the leads on your scope (or meter) and not resetting the readings could be a reason for the testing procedure to be the cause. If you didn't do that then where's the voltage? It's MIA. Voltage has to take priority over everything else because it affects everything…
Holy hell Guido. How did I miss that????
Hi Martin: It happens to me much more than I like. I do understand. Multitasking claims another. Guido
Here is a power point presentation to break this system down to laymen's terms. It should help with your testing using DMM and or Scope! Like all have said check the integrity of all ground straps and harness connectors for (green) corrosion. You can contact me for questions or other on this content. Disclaimer: I have not updated this content in over 10 years.
Is this available for download somewhere? T…, Noah
There is a download Icahn in theupper right hand corner once you click on the attachment
Must have missed it, thank you for the reply (and the power point)
Thanks everyone for all the input. This vehicle is repaired. I learned what I should have done (or done more thoroughly) and I think Guido hit on one of the first things. Multitasking. Slow down and analyze what you are doing (and have done). John and Matthew it was in fact a bad ground on the van. I work for on a fleet and I rarely get any major diagnostic repair work that requires me to break…