Fuel Codes

GordnadoCRD · **Posted:** Tue Feb 14, 2017 12:38 am

I have 2 fuel codes persisting,

P0088 - Fuel Rail Pressure too high
P1202 - Fuel system overpressure- Stuck Regulator

but I can't find any information on whether it relates to the FQS or the FPS.

Fuel pressure is definitely high, around 11k at around 1200rpm.

It will start and idle for a few seconds, then dies, if the go pedal is untouched. If I start it will run for several minutes as long as the revs stay over 1000. 950 or below = stops like the key were shut off. If I leave it at 1100rpm it will run till it's nearly warmed up, then die no matter what the rpm (I"m assuming that. I've not taken it over 2000 due to the over-pressure situation.

Anyone come across this before?

TIA

flash7210 · **Posted:** Tue Feb 14, 2017 11:51 am

This is gonna be tough to diagnose.

The fact that it wont maintain its normal low idle tells me that there may be insufficient fuel pressure and therefore the problem is a bad fuel rail pressure sensor.

The fuel rail pressure solenoid usually fails in the open position, not allowing pressure to build in the rail. If it were stuck in a closed position, that would create a too high pressure scenario.
If you unplug the rail pressure solenoid the engine should not be able to run at all. Therefore, if the engine continues to run after unplugging it, that could indicate a stuck rail solenoid.

The fuel quantity solenoid (on the CP3), when unplugged, will send all fuel up to the rail. But under this open circuit condition, the engine should still run and idle normally but will throw a code for the open circuit and will be in limp mode. If it were somehow stuck in some position, the rail solenoid should be able to compensate for a overpressure event.

GordnadoCRD · **Posted:** Tue Feb 14, 2017 2:13 pm

I can throw in a couple more bits of info now, and add that to what you've told me.

When I unplug the FPS, the engine does not fire at all, and adds Fuel Pressure Regulator 1 control circuit open. Plug it back in, and it returns to the afore mentioned condition.

When I unplug the FQS the condition remains the same, but adds the code P2294 - Fuel Pressure Regulator 2 Control Circuit Open.

So it would appear that the regulator that is stuck is the FQS, since even though it sensed it was unplugged there was no change in running behavior.

In that scenario the auto shutdown is probably related to a CP3 protection condition. Heat maybe?

GordnadoCRD · **Posted:** Tue Feb 14, 2017 2:33 pm

Everything is passing the open circuit tests. The FPS has a separate ohms resistance test, which this one passes. I can't find any independent way to check the FQS or the fuel pressure sensor.

flash7210 · **Posted:** Tue Feb 14, 2017 3:24 pm

I'm not yet convinced its the FQS.

How are you reading rail pressure, with torquepro?

Try clearing all the codes, then startup the engine and disconnect the rail pressure sensor.
Torquepro should then display a rail pressure of ~26,000 psi.
You should also get a P0193 code.

If with the pressure sensor unplugged, the engine runs steady without dying, the problem is likely the sensor.

I had some fuel system problems about 1.5 years ago. Replaced the rail pressure sensor and FQS. Turned out that the actual problems were at the wire connectors where they both would have a intermittent open circuit.

GordnadoCRD · **Posted:** Tue Feb 14, 2017 4:53 pm

flash7210 wrote:

I'm not yet convinced its the FQS.

How are you reading rail pressure, with torquepro?

All code and readout info through Snap-On

Try clearing all the codes, then startup the engine and disconnect the rail pressure sensor.
Torquepro should then display a rail pressure of ~26,000 psi.
You should also get a P0193 code.

I'll try. Usually it won't idle long enough for me to get there. 5-6 seconds, tops.

If with the pressure sensor unplugged, the engine runs steady without dying, the problem is likely the sensor.

Will check.

I had some fuel system problems about 1.5 years ago. Replaced the rail pressure sensor and FQS. Turned out that the actual problems were at the wire connectors where they both would have a intermittent open circuit.

I also discovered that I didn't get the new fuel filter on tight enough. The new Cummins-Carter in-tank pump informed me quite pointedly.

GordnadoCRD · **Posted:** Tue Feb 14, 2017 7:37 pm

More Data:

Before disconnecting the F. P Sensor, I did some tests.
Cold cranking, fuel pressure read 1305psi, volts 0.52 set-point was 7975

fuel pressure when it fired briefly <1 sec 3665 psi, volts 0.8 set-point dropped to 6865

Idling - smooth, for 6 seconds before dying 7975psi didn't get the volts, the set-point raised to 8000+, didn't get the exact # as it changed after it died.

Then the excitement started.
I unplugged the fuel pressure sensor

it did start. sort of, definitely not smoothly as before, and within 15 seconds I had to off the key, and run out of the shop, and I could barely see through the cloud of un-burned fuel to get there. I had an extend-a-pipe connected to outside and all. The body shop next door thought the place had caught fire.

After we had let all the warm shop air go~ :furious:

~ I started it again, but this time I was in the drivers seat, and when i touched the accelerator, everything smoothed out, and ran beautifully... as long as I had at least 1% accelerator applied. So I went ahead and warmed it up completely. even fully hot, when I let off the accelerator it seems to drop to 1 cylinder idle and a S~t-ton of the blackest I mean COAL black smoke out the exhaust. But it DOES run, and that is a difference.

The other difference is the new P1090 Fuel Pressure Sensor Circuit Malfunction code, but you knew that was coming.

Two questions:
1) are these pressure numbers in line with what one could expect from a properly functioning fuel pressure sensor assuming the possibility that the FQS could be stuck?

2) does the result of unplugging the F.P. Sensor indicate it is bad?

It seems to turn me somewhat back towards the FQS , and that the fuel pressure solenoid is able to compensate for the over-volume and over-pressure except at idle somehow. Does the ECM of the CRD revert to an open-loop map state at foot-off idling like a gasser does?

flash7210 · **Posted:** Wed Feb 15, 2017 12:27 am

Ok. Now it does seem like a FQS problem.
Even with the sensor unplugged there should not be huge amounts of black smoke. That is definitely waaay too much fuel.

GordnadoCRD · **Posted:** Wed Feb 15, 2017 1:46 am

Hope Y'ALL are having a great V-Day.

I spent too much time in San Diego. I look forward to March 20.

All that aside, I think I may have found the issue, doing all the tracing stuff, I found that wire-to-wire resistance between the FQS leads reads 4.1 ohms with the fqs unplugged and the ECM unplugged. Spec is 1000+ ohms.
So I'm head down, feet up, chasing a wiring loom issue again.

On another issue,
Whomever came up with the line that this stuff https://www.amazon.com/Rescue-Tape-Self-Fusing-Silicone-Rectangular/dp/B00AZOK55G doesn't stick to anything but it's self needs to be throttled by my nitrile work gloves.
I tried using that stuff last night... I invented a few new swear words and must have looked like a monkey fighting a fly strip.

GordnadoCRD · **Posted:** Wed Feb 15, 2017 3:52 am

Even More Data

I got the electrical bugs out of the loom, and proceeded through the ALLDATA checklist and got to the final page.

ECM check for open circuit DTC
Ignition OFF
Disconnect the Fuel Quantity Solenoid harness connector
Ignition ON
With Scan Tool, erase ECM DTCs
Monitor scan tool for active ECM DTCs
The scan tool should display P0090 FUEL QUANTITY SOLENOID OPEN CIRCUIT
Mine displayed P2294 FUEL PRESSURE REGULATOR 2 CONTROL CIRCUIT OPEN.

ECM check for short circuit DTC
Ignition OFF
Disconnect the Fuel Quantity Solenoid harness connector
Ignition ON
With Scan Tool, erase ECM DTCs
Monitor scan tool for active ECM DTCs
The scan tool should display P0092 FUEL QUANTITY SOLENOID SHORT CIRCUIT
Mine displayed P2296 FUEL PRESSURE REGULATOR 2 CONTROL CIRCUIT HIGH.

Q: Does the scan tool display the appropriate DTC for each condition?

YES = Replace FQS
NO = Replace ECM and program it.

To my mind, what they say and what mine says, basically have the same meaning, but I don't know just how identical they have to be.

Caveat: One of the old stored codes that I erased was VIN does not match, and a different one VIN not programmed. Neither have returned since I cleared codes, but it suggests to me that my ECM was changed at some point. Probably after whatever accident this thing was in, so is it possible it could be from an import?

If the ECM is buggered would GDE be able to re-program it or determine if it's rescue-able?

EDIT: One other thing I hadn't noticed before. Now that it's quiet, With the engine OFF and key ON; when I have everything plugged in, the Fuel Pressure Solenoid at the rear of the rail clicks at the rate of about 3 per second. Unplugging the Fuel Pressure Sensor makes no change. Unplugging the FQS makes it stop. Again, this is with the engine off, so why is it trying to dump fuel?

GreenDieselEngineering · **Joined:** Sun Jun 07, 2009 5:10 pm **Posts:** 1111

The problem should be a failed pressure control valve (PCV) on the back of the fuel rail. It is sticking. If you did recent service on the CRD, the #4 injector and the PCV wiring can be interchanged. It usually will not run if this happens. Most likely the PCV needs replaced. They are quite expensive around $400+. Might be able to find a junk yard rail with the PCV for cheaper. We have seen a few of these fail on higher mileage vehicles. Hope this helps.

GordnadoCRD · **Posted:** Wed Feb 15, 2017 9:10 pm

Thank You, Keith, for your time and expertise.

I checked with Oregon Fuel Injection on their website, and found that their price for a completely rebuilt-with-warranty fuel rail including Fuel Pressure Valve AND Fuel Pressure Sensor already installed, is less than they want for just the Fuel Pressure Valve alone. I even called them to verify that the electronic parts are included and properly installed.

Whomever does the rebuilding has a core charge of $300, and it seems they're the only ones doing it, because everyone that sells these charges the same $300 core in addition to their price.

GordnadoCRD · **Posted:** Sat May 06, 2017 11:46 pm

This problem still continues.
Here is the status presently:
SOOOO
I haven't found the cause of the "start great, then choke and die ~7 seconds later" syndrome.

In tank pump is working fine

No air in fuel

Starts almost immediately, idles great for ~ seven seconds, then choke and die.

Engine Codes are p0088 and p1202

Fuel pressure is high. Always. Does not go low then spike. Does not fluctuate.

3 different fuel pressure sensors give exactly the same numbers. 11k-12k psi.

if I immediately use the accelerator pedal to bring RPM to ~1700, then fuel psi set point, and psi actual are close enough that I can sometimes keep it running for a while. If RPM falls and set point drops, it will choke and die.

FQS is new. Changing it made no difference.

Rail Fuel Pressure Solenoid (FPCV) is new. Changing it made no difference.
Weirdly, changing between 2.8CRD and GM Duramax FPCV's also makes no difference. Not running yet. so still can't say whether the Duramax one will work.

Disconnecting either FQS or FPCV results in a properly identified circuit fault by ECM

FPCV passes NO fuel when cranking. Once engine fires it splatters everywhere if not safely ended in a good container. When it dies fuel stops immediately.

Checked for blockages in fuel return circuit. Fuel flows freely to tank. No leaks.

Manually propping the throttle to 5-7% (per scanner) can also keep it running for a while ....sometimes. usually this results in a large RPM increase, (when system goes closed loop) followed by dying.

It will never idle for more than a few seconds

Tried loading Yeti's 808 mild tune with FCV delete. Loaded with no problems. Made no difference, so likely not ECM or tune related.

All sensor wires traced and tested for shorts grounds continuity, and resistance. All pass perfectly.

I've run out of things to check and change. I thought for sure the new FQS would fix it, but no change whatsoever.

I haven't found any sensor with unexpected readings, exc the fuel pressure being way high, and no idea why it's doing that.

Kind of acts like a key chip not passing security check, but that would show on the dash AND throw a code. It does neither.

Body Codes
PCM messages not received
VIN message not received

Transmission
no codes present

Anyone else ever had this problem?

Mountainman · **Posted:** Sun May 07, 2017 1:02 am

I'm thinking that it has to do with those body codes because 7 seconds is a long time in ecu land. The one I had that had a burnt fqs pin wouldn't start at all. If it gets too hard to find I'll send you a complete fuel rail to try just in case the GM sensor is however unlikely the culprit. I think if the fqs was out of parameters that it wouldn't start though.

GordnadoCRD · **Posted:** Sun May 07, 2017 2:04 am

I actually have 2 rails currently. My original one has a new fuel pressure sensor, which gives the same reading as the original pressure sensor, and the new GM Fuel Pressure Control Valve.
I have a second rebuild rail, with all new sensor and valve for the 2.8CRD.
But with both of them behaving exactly the same, it's got to be something else, and about the only thing left is the ECM.
Next week I'll have an oscilloscope here, so I can see if the transistor signals for the FQS and the FPCV are still commanding square wave signals or if they're breaking down. Also what duty cycle it's sending the FQS. With the pressure so high, if it's not commanding 100% or close to it, then that would be the problem.

WolverineFW · **Posted:** Sun May 07, 2017 12:53 pm

Is this still happening with the new rail, solenoids and sensors?

GordnadoCRD wrote:

EDIT: One other thing I hadn't noticed before. Now that it's quiet, With the engine OFF and key ON; when I have everything plugged in, the Fuel Pressure Solenoid at the rear of the rail clicks at the rate of about 3 per second. Unplugging the Fuel Pressure Sensor makes no change. Unplugging the FQS makes it stop. Again, this is with the engine off, so why is it trying to dump fuel?

Sent from my SM-N910W8 using Tapatalk

GordnadoCRD · **Posted:** Sun May 07, 2017 6:25 pm

Actually that was my bad hearing. My nephew corrected me that it was actually the FQS that was doing it. I couldn't feel it in either place, but could hear it better with my head up, than down by the alternator space somehow. It does it anytime it's unplugged and plugged back in, and doesn't matter which FQS I use, or which rail I use.

flash7210 · **Posted:** Tue May 09, 2017 2:50 pm

Just had a thought...

Turn the key on and clear the codes, then turn the key off.
Unplug the fuel rail pressure sensor.
Then turn the key on and start the engine.

With the pressure sensor unplugged, you cannot get a P0088 "pressure too high" code.
The engine should be able to start up and run, but will be in limp mode.
You should definitely get a P0193 code.

If it doesn't start up and run, disconnect the FQS.
This should generate a P0091 code.

Two years ago when I was going through fuel system problems, there were times where the only way I could get the engine to start and run was by disconnecting both the pressure sensor and FQS.
Obviously, my rail pressure solenoid was still functional.
I also didn't get any abnormal amounts of black smoke.

GordnadoCRD · **Posted:** Tue May 09, 2017 5:53 pm

my best James May impersonation...

GOOD NEWS!!!!
Well, Mostly
The bad part is I've done something really stupid.
Unfortunately, that's not new.

Quote:

The fact that it wont maintain its normal low idle tells me that there may be insufficient fuel pressure and therefore the problem is a bad fuel rail pressure sensor.

This, I now know is not the case. as confirmed by multiple pressure sensors.

The fuel rail pressure solenoid usually fails in the open position, not allowing pressure to build in the rail. If it were stuck in a closed position, that would create a too high pressure scenario. But that is basically impossible

If you unplug the rail pressure solenoid the engine should not be able to run at all. Therefore, if the engine continues to run after unplugging it, that could indicate a stuck rail solenoid. Again, impossible in this circumstance.

The fuel quantity solenoid (on the CP3), when unplugged, will send all fuel up to the rail. But under this open circuit condition, the engine should still run and idle normally but will throw a code for the open circuit and will be in limp mode. If it were somehow stuck in some position, the rail solenoid should be able to compensate for a overpressure event.] ALL true

When I originally bought this little monster, (in spite of motor oil running out the tailpipe, and the fact it would only idle, as any attempt to rev it would make it nearly hydraulic lock,) We assumed the way it was wired was basically correct. Part of the problem was my brother and I divided up the disassembly by which side of the engine bay we were working from, so neither of us saw the whole picture.

Much later, when all going back together, he was busy with heavy snow winter overtimes so I was the main re-assembler. Back in January / February when I was running pin-outs and chasing gremlins of various origins, a weird thing I came across was that the wires to the Fuel Pressure Control Valve on the rail, (1) was that the wires were in their own loom from the ECM, and that (2) they were a few inches too short, due to now having new engine mounts. I added some length, and continued on.

After running into the start-choke-die problem I went back to check these, checked the FQS wires, (which weirdly had been cut, more about that later) and color matched them to the back of the ECM and hooked them up as seemed proper.

No change
Many parts and much time and money later.
still no change.

Today, I was going back through the Pin diagram for the ecm, and realized something I had noticed before but skipped over as just another error in the Factory Service Manual. This was that the wires from the Fuel Pressure Solenoid Supply were hooked into the
pin marked Fuel Quantity Solenoid Supply. When I noticed this before, I had taken the separate loom going to the FPCV (rail) and routed it to the FQS (pump), but when I turned on the ignition power, the computer went berzerk and popped up 14 codes and things that couldn't possibly be related. When I moved it back up to the rail and cleared the codes, they all went away exc these P0088, P1202, (and the EGR/FCV codes which I was ignoring).

This time I traced both the FQS and FPCV wires and they were exactly all 4 100% backwards from what the FSM said. So just to verify it was a book error, I switched all 4 wires to the labelled pins via jumpers. Turned the key and, it started just like before, but

GOOD NEWS!!! no choke, no die. no codes

:oops:

When I discussed this with my brother, we came to the realization that when I bought it, someone had cut the FQS wires, so it was always 100% delivery, and wired the FQS output to the FPCV on the rail, outside the other loom. And had pulled the FPSensor connector so that the computer was always limp home mode but wouldn't die at idle. (sensored word) So basically what was happening, was the engine would start fine, but when the ECM would enter the picture, it would tell the FPCV on the rail to bleed off more fuel, This would actually send a message to the FQS to send MORE fuel. When it would send a message to the FQS, to stop sending more fuel, this would actually send a message to the FPCV on the rail, to Stop bleeding fuel, and close up tighter!. = Way high pressure = p0088 and p1202. Now that messages are going where the computer always thought they were, everything is AWESOME!!

So now I get to pull the temp jump wires, and rewire everything properly.
This also means that all of the pressure sensors I bought, the rebuilt rail, Even the FQSs and the FPCV I cut apart, although definitely worn, were probably not actually failed yet.

But guess what...

MORE GOOD NEWS!!!

The $90 Duramax FPCV on the rail works perfectly. Absolutely flawless

I already sent the new "rebuilt" rail back for refund. That's $550 I can definitely use elsewhere.

I guess the grain of good in this episode, is don't immediately assume the book is wrong, even if the jeep tells you it is. Fully verify it first.

flash7210 · **Posted:** Tue May 09, 2017 6:42 pm

OMFG

Lets see if I can figure this out...

1. Previous owner had smoke pouring out the exhaust.
2. Thought is was a fuel system problem.
3. Tried to fix it by re wiring the fuel pressure solenoid.
4. Made the problem worse.
5. Sold the mess to you.

Best part of all this is that you finally figured it all out.

The second best part is this.

Quote:

The $90 Duramax FPCV on the rail works perfectly. Absolutely flawless

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