So today I installed a new fuel pump assembly and a picknpull ipdm. I go to put the ignition on and after a few minutes the “Service engine soon” light comes as in sequence with the fuel pump turning off and on. The light and pump will turn on and off with each other. Only code i’m getting is about a knock sensor bank 1 and I don’t think that will cause this issue. I am thinking the ECU is toast. I’ve checked the ecu fuse and relay as well as the fuel pump fuse and relay. I’m lost at this point. Anyone got any ideas?

Thanks in advance!

 

Check the fuel pump harness to make sure you didn't bend a pin.

What code is it throwing?

 

What was wrong with your previous IPDM? Was the replacement exactly the same? There were multiple revisions/part numbers and it's not the first time on this forum where someone swapped a used one in and had odd behavior after.

 

I got the used IPDM from another '03 and I changed it because I was reading that the IPDM could be the cause of the fuel pump not turning on. When I first got the car it didn't crank and I was told it was down for 3 days. I started with a new starter and battery to fix the crank issue but the car still wasn't starting. The fuel pump wasn't turning on so I went and got a used '03 IPDM from pick n pull and installed it, the harness was the same and everything clicked in correctly. I did notice when first testing with the new IPDM that the windshield wipers were staying on constantly when the battery was connected, so I pulled the fuse. I may try and put the old IPDM back in and see what happens. I've ordered a refurbished ECU from flagship one to hopefully fix the issue.

 

So I put the old IPDM back in and it fixed the issue with the wiper staying. However, the fuel pump no longer is pulsating and there is no SES light along side that pulsation. I think I've narrowed it down to a bad ECU at the moment until I can get it in the mail and installed.

 

Sounds like that donor IPDM was wet, that's a typical cause of stuff like that. When they get wet it causes relays to short out like that even though they're not getting signal from their controlling device.

Before you declare the ECM to be bad, have you bench tested the fuel pump relay, verified the ECM is NOT sending the signal to the IPDM to close the fuel pump relay, etc.

ECM pin 113, black wire/orange stripe is the controlling circuit, backprobe the ECM and see if it's delivering no voltage for approximately 1 second when you turn the ignition to ON, then after the 1 second it should be delivering 12vdc. That's going to the coil side of the relay.

If it's sending the signal then the problem is not the ECM.

Next, the IPDM, power goes through fuse 81 (15amp) to the fuel pump relay contact side on the black wire/yellow stripe. This goes directly to the fuel pump and you can measure voltage at the pump, same black wire/yellow stripe.

This will let you pinpoint EXACTLY where the issue is.

 

Thanks for all that info! I have a question though, when the ECM harness is plugged in, how would I go about getting that signal? Would I read it from the IPDM?

 

Also, I just wanted to add the donor IPDM was very clean inside and out. I think the problem was with it came from a sedan '03 where as my car is a coupe. I've read online that the "model" number has to match or some things will act up. Even though the outside layout is the same they say the internal routing of the wires is different slightly.

 

You will need to "backprobe" the ECM, if you don't have backprobe leads you can straighten out a paperclip then stick it into the back of the harness. Typically you would then attack your digital multimeter leads by using aligator clips onto the backprobe leads. Just be careful not to let your backprobe leads touch ground since it will be energized, if it's in too close of proximity to ground source I typically just stick a little electrical tape on them to minimize risk.

This should be the layout for your ECM harness, easy to find pin 113 black wire/orange stripe since it's in a corner by itself.

 

Here's that page from the FSM with the fuel pump schematic in case you need a visual of how it works. It's the same across all years of coupe from 2003-2007, I think the coupe used the same shape ECM harness across all years.

 

I was able to get a paperclip in pin 113 and I got a constant 12v, not sure . I tested the fuse incorrectly, I don't know why I thought I could read voltage by probing both ends of the fuse while it was in. I'm gonna be retesting the fuse soon and I'll get back to you.

 

I was able to get 12v from the ECM, 12v to the fuel pump relay fuse and 12v from the fuel pump WHEN it was "pulsating". While the pump was unplugged a relay from the IPDM was clicking over and over again as well as the SES light was flashing. I scanned the car and found one code which was P2135, a voltage difference between the acceleration pedal sensor and the throttle body position sensor. I'm not experience enough with this car enough to know if that would cause this strange fuel pump issue.

 

That's not the reason for the relay to chatter. So it only chatters when the fuel pump is unplugged?

Sounds like you have a bad ground, are both connections on the battery tight? Is the battery fully charged? Does the engine crank nice and strong?

It sounds like either a bad relay or a damaged IPDM. I would take that IPDM apart and see if it's wet on the inside. Look for any obvious signs of water damage like corrosion.

 

I was using a battery from my daily driver which had 12v and it was cranking good. I will say the positive and negative terminals aren't the best and won't have the snuggest fit but its enough to make a strong connection, I made sure they're as tight as they can be. I will buy them soon, does the negative cable have to have two holes on the end that bolts to the chassis or is on hole good? I saw one at AutoZone for like $10 and wanted to give it a try.

The IPDM did have some oxidization on the external terminals and had two relay posts internally which seem to be corroding but they were still strong and we're bridging. However, that doesn't mean they weren't the cause of a previous short from the past since the IPDM is in the worst spot ever.

Could a bad IPDM be causing these weird issues with the fuel pump getting intermittent power? I swapped the fuel pump relay and the A/C relay to make sure it wasn't just a bad relay and the same issue occurred.

Also, I think I might get out and check if maybe the fuel pump output from the ECM is on and off as well, then I can determine if its from the ECM causing the power loss.

Thank you for helping me through this all, you're awesome.

 

Sounds to me like a bad IPDM.

As for the negative battery cable, no you can make do with a single lug on the chassis side as long as it's electrically clean and the correct size conductor it will be fine, battery cables are usually either 4AWG or 2AWG. I don't know off hand what size the G35 is but if you have the existing cable you can scrub off the dirt on the insulation and probably find the factory wire size on it.

As for the battery, when you have it tight you cannot turn the post lugs by hand correct?