CP4 diagnose P228C P228B

M.A.M.

Member
Jan 9, 2016
413
3
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Ohio
Looking for a little bit of help in diagnosing a low rail pressure issue, as well as some info on these stock lift pumps.

P228C Fuel Pressure Regulator 1 Control Performance - Low Pressure

P228B Fuel Pressure Regulator 2 Control - Forced Engine Shutdown

Running the big tune and towing. Leaning on it in the hills, rail pressure drops down into the low 20s and desired is 26-28k. Lift pump pressure holds steady @ 55-65 psi. Throws the 228C. If I keep my foot in it for longer than 10 seconds, it will throw the 228B code and go into limp mode. Shifting down into fourth, the pump will hold 28k desired and actual. It will still drop slightly if I really lean on it.

I’ve had a few different shops try to sell me a lift pump saying I need one to run that big of a tune. IMO, A bigger lift pump pushing more psi won’t do anything for me since the stock one is still pumping fine, right? IIRC, the Fass pushes around 80psi and needs pressure codes turned off because of it.

I’ve ran like this for 65k miles already, and only recently started to throw these codes. Is the stock HP4 just getting weak? Will measuring the fuel return rate while the engine is running tell me anything, or not?

If the ECM pulls power because of a hurt transmission, could it show up in this way, or not?

I replaced the driver side fuel rail including that regulator, since I know that they can have an issue with sticking. No change. Looking for any help in diagnosing before I blindly throw a bigger injection pump at it.


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Chevy1925

don't know sh!t about IFS
Staff member
Oct 21, 2009
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Phoenix Az
whos tunes? have you ever logged rail under the same circumstances prior to the truck starting to throw the codes?

you may have been dropping rail before but not enough to throw the codes, now you finally hit the bench mark.

btw, we need more details on the truck. your sig is not an L5P based rig lol
 

M.A.M.

Member
Jan 9, 2016
413
3
18
Ohio
Kory’s tunes. Truck is 2017 with 315k mikes on it. Truck was tuned at 250k. Tow pig, right around 26K gross.

I’ve got an edge monitor in the truck, and always watch the desired versus actual. Run I-77 north and south a lot, and run the WV hills pretty hard, that’s why I’m surprised it never came up before. Very possible that it had been dropping rail a bit before, and I just never caught it.


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PureHybrid

Isuzu Shakes IT
Feb 15, 2012
2,590
4
38
Central OH
How long do the HP4 pumps last? If it was a cp3 with those miles everyone would say the pump is bad. Is it a pain to measure the return rates?
 

Chevy1925

don't know sh!t about IFS
Staff member
Oct 21, 2009
17,374
97
48
Phoenix Az
the hard part is not knowing how it was doing prior. could be that it needs just a tuning tweak (the low pressure at lower rpm vs good pressure at higher rpm has me thinking that) but at 317k on the clock, it could have some worn out injection parts that are not helping.

So the fun starts now in testing to find the issue/s.
 

M.A.M.

Member
Jan 9, 2016
413
3
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Ohio
My thought initially was also that the injection pump is going out. Injector balance rates all look good.

Measuring how much fuel is returned during 15 seconds of cranking only tells me if any injectors are leaking, right?


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DPC

Member
Jan 2, 2012
303
1
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Adams, TN
Have you already changed the fuel filter to rule that out? A shop with a good scanner should be able to max out the pump pressure and see if it holds.
 

M.A.M.

Member
Jan 9, 2016
413
3
18
Ohio
Have you already changed the fuel filter to rule that out? A shop with a good scanner should be able to max out the pump pressure and see if it holds.

Yeah, brand new filter when it started throwing the codes. I’ve got a snap-on scanner, that was the next thing I was going to try. Probably will be this weekend before I’ll have time to mess with it tho.

Didn’t I see some reports of the pumps going bad immediately?

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I’ve heard of a few. Dad’s went out in his L5P @ 30-40k, had the whole fuel system replaced under warranty and no problems since.


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DPC

Member
Jan 2, 2012
303
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Adams, TN
You could also try one of the smaller tunes and see if it holds. If the lift pump pressure is good the only thing left is the HP4 or injectors... if the Allison is pulling power you won't see it in the fuel pressure because the actual and desired will be the same.

You could also log data with your HPT.
 

M.A.M.

Member
Jan 9, 2016
413
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Ohio
I’ll have to dig my computer out and turn it down a bit, literally hasn’t moved off this tune since it was flashed in.


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RickL5P

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Jul 1, 2020
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My 2017 L5P has been shooting P228B P228C when I'm towing pulling up in the hills. It's been to the dealership 3 times for the same reason and they kept saying everything is fine. lol so today I loaded it and took the tech for a ride up the hill. They now see the problem and are replacing the HP4 pump and injectors.
 

M.A.M.

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Jan 9, 2016
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Ohio
Finally got some time this evening to check out the return rates for the injectors and pump. I know I’m a procrastinator, you don’t have to tell me.

Here’s what I did, tell me if I did something wrong. Never checked return rates before. Pulled the rubber hose off of the last injector on each bank before it gets dumped back into the main return. Plugged the nipple that goes to the main return, and dumped the rubber hose off of the injectors into a can. Took off the fprv hose and dumped it into a can, and plugged the nipple going to the main return.

Disconnected the main return quick connect on the driver side, and ran a hose from it into a can.

Pulled the ECM relay, hit the key, and the starter would crank for 15 seconds at a time.

Never got a drop of fuel off of either injector bank return. I even stuck the relay back in and started the truck up, and still didn’t get as much as a squirt out of the return for either bank, while it was running.

This is what I got out of the main return, which if I understand correctly is what the pump is returning, unless I screwed something up and that was the pump and injectors returning together.




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M.A.M.

Member
Jan 9, 2016
413
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Ohio
Got some good info from a buddy that wrenched at a dealership.

With the injectors unplugged, and cranking for 15 seconds, there’s isn’t supposed to be any fuel coming out of the injector returns at all. So we’re good there, I couldn’t even get a drop.

Max return spec for regulator #2 and cranking for 15 seconds is 15mil. I’m returning 55ish. Same return rate spec for the #2 regulator while the truck is running, 15mil. I’m getting around 20.

Regulator #1 keeps up with commanded all the way up to 17k, so that’s ruled out.

GM diagnostics don’t give any procedure for measuring pump return. Just says replace pump if all the other tests pass.

I replaced the entire drivers side rail including the reg2 about 40k miles ago when this issue started. Didn’t change anything at all.

I’m leaning towards replacing the pump and the regulator itself, and seeing if that takes care if the issue, since the new regulator and rail didn’t do anything for me.


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lutzjk913

Active member
May 5, 2010
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groveport, ohio
Got some good info from a buddy that wrenched at a dealership.

With the injectors unplugged, and cranking for 15 seconds, there’s isn’t supposed to be any fuel coming out of the injector returns at all. So we’re good there, I couldn’t even get a drop.

Max return spec for regulator #2 and cranking for 15 seconds is 15mil. I’m returning 55ish. Same return rate spec for the #2 regulator while the truck is running, 15mil. I’m getting around 20.

Regulator #1 keeps up with commanded all the way up to 17k, so that’s ruled out.

GM diagnostics don’t give any procedure for measuring pump return. Just says replace pump if all the other tests pass.

I replaced the entire drivers side rail including the reg2 about 40k miles ago when this issue started. Didn’t change anything at all.

I’m leaning towards replacing the pump and the regulator itself, and seeing if that takes care if the issue, since the new regulator and rail didn’t do anything for me.


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Judging by what you said I think your on the right path.
 

RickL5P

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Jul 1, 2020
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Sounds good. Mine is still in the shop and everything is being replaced. The pump, injectors, rails and lines from what GM told me.
 

M.A.M.

Member
Jan 9, 2016
413
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Ohio
Just wanted to leave an update that a new injection pump fixed the issue. We are back to hauling ass up the hills, and rail pressure stays solid.

Edit: should add that fuel temps were getting pretty high. 140+. Temps stay right around 75° with the new pump. Obviously a sign of returning too much fuel. Engine will derate once fuel hits 140°.


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