LMM: P0090 Rail Pressure Rattle..New FPR.

[6speedduramax]

On the way home from Antrim last month, after just filling up at the station by the track, my truck started getting the loud injector rattle that comes along with the rail pressure being to high from a bad or disconnected fpr. Shortly after the truck went into reduced power mode and a P0090 code came up. Assuming it was a bad fpr I got the truck home, replaced the fpr, and no difference. Any ideas? Need to get it going soon, the girlfriends ss cobalt sucks for a construction vehicle and sucks even worse in the snow..

 

[6speedduramax]

Anyone?

 

[02greysixer]

On the way home from Antrim last month, after just filling up at the station by the track, my truck started getting the loud injector rattle that comes along with the rail pressure being to high from a bad or disconnected fpr. Shortly after the truck went into reduced power mode and a P0090 code came up. Assuming it was a bad fpr I got the truck home, replaced the fpr, and no difference. Any ideas? Need to get it going soon, the girlfriends ss cobalt sucks for a construction vehicle and sucks even worse in the snow..

Probably in the pigtail going to the fpr or the bulk connector on the d.s. valve cover. I think it's the top one. Try wiggling them with the engine running. If engine sound changes it's a wiring issue.

 

[6speedduramax]

Wiggling the pig tail made it straighten up for a couple seconds.. Just not sure if its in the pigtail itself or the main harness at the pigtail..

Why does the harness side of the pigtail have three wires and fpr side only have two?

 

[Robby Avery]

Try placing a light coat of die electric grease on the connector ends and see if that helps smooth it out also try using a zip to pull the connector either in tighter or up or what eve position causes it to smooth out I had a similar truck I worked on it was 06 LBZ that had a intermittent problem at c107 it was due to terminal contact not fully seating I had to quote the gentleman the whole harness due to the number of wires present and the risk of possibly placeing a wrong terminal in the wrong location on a harness connector rebuild just to much of a risk how ever the die electric grease to seem to correct the problem and the guy was perfectly happy not having to purchase the whole harness

 

[02greysixer]

Wiggling the pig tail made it straighten up for a couple seconds.. Just not sure if its in the pigtail itself or the main harness at the pigtail..

Why does the harness side of the pigtail have three wires and fpr side only have two?

The 3rd wire is the shielding wire. It is wrapped around the other 2 and ends just before the fpr plug. The di-electric grease is a good idea. May also try carefully ice picking the connectors. Search "lly ice pick fix" or similar. Same principle.

 

[6speedduramax]

if I shake the main harness where the pigtail plugs into it, it fixes the problem but I cant actually find the bad spot on the wiring anywhere... Ill try the dielectric grease. whats a shielding wire do? Protection only? I tested it with a voltage meter and it had 3.5 volts on one pin with the other pin on the battery ground.. but when I went from battery power to the opposite pin I had nothing so it must be an open ground it seems..

 

[02greysixer]

Did you pin drag connectors or try staking the female pins? I don't remember specifics on voltages or grounds for that circuit. I'd have to look it up again. But I suspect your issue is in the female pins since you say it clears up if you wiggle the plug there. I suppose you could hardwire it from fpr to main harness. Not sure how it will behave without shielding wire though. It will likely be fine but can't say for sure, never tried it

 

[6speedduramax]

What exactly does the shielding wire do?

 

[02greysixer]

My understanding is it is there to help block interference with the signal from pcm to regulator from the alternator, radio, and other sources. And keep the fuel pressure regulator signal from interfering with other circuits

 

[6speedduramax]

Ah ok that makes sense.. Do you know if the sheilding wire is attached to ground? Or what it is attached to?

 

[02greysixer]

I believe it does ground somewhere yes. I'd have to look at the schematic again to be sure though

 

[clrussell]

Check pin 33 & 37 on the main junction connectors on the engine for bad connection.

Also check pins in the 3 wire connector going to the fpr, make sure they are tight.

 

[clrussell]

That should be the top connector on your engine, the smaller one.