Fuel Pump Threw Low Pressure Codes

[TallPaul]

So I left Detroit Thursday am (-10F) and headed for Florida. About 300 miles along, the "Service Engine Soon" light came on. Drove another 300 miles and had the codes pulled the next morning. They said the codes were low fuel pressure, and said it was putting out about 22 psi instead of what it should be around 40+. This was from the scanner, they did not put a fuel pressure gauge on it. Also, I never noticed any driveability problems, seemed to have full power all the way, so if there was low pressure it was hardly noticible in the performance.

Shop turned off the light and said not to run below half a tank (this is a motorhome with 55 gallon tank) I consistently filled up at half on the gauge and it took about 30 gallons each time. Made it another 640 miles and so far the light has not come back on. So not I have 1240 miles home.

So does the half tank of fuel cool the pump by the fact that the pump is at least partly submerged in the fuel, or does it cool it by the fact of the fuel flowing through it and too low of fuel allows the fuel to heat up too much?

Also for any tech people, it's a 2000 Chevy cutaway van chassis with 454 V8 (7.4L), it's a one ton, 3500 series, with 21,000 miles on it. The actual codes were (as the tech wrote it on a paper):

FUEL TRIM
BANK SENSOR
BANK 1 2

Anyway, looks like I am good if I keep it no less than half a tank. Once back in Detroit area and in the spring when the weather warms, I'll run it low and see if it will throw more codes. Hate to change out the fuel pump if this was either

1) a fluke that won't likely happen again, or

2) a false code (is that possible?).

Thanks,

 

[The_Jeff]

I'll throw my hat in here and mention I had a 92 dodge dakota 3.9 that required, IIRC, 45 PSI. Fuel pump was dying and it fluttered between 5 and 20 PSI and still ran tolerably!!

If you have more gas in the tank, the pump doesn't have to raise the level as much which helps a bit.

Harbor freight has cheap gauges for ~$15, they can double as a way to pump gas out of the RV if you use it as a crisis reserve fuel supply. I would get a real gauge on there pronto.

 

[demarpaint]

Originally Posted By: eljefino
I'll throw my hat in here and mention I had a 92 dodge dakota 3.9 that required, IIRC, 45 PSI. Fuel pump was dying and it fluttered between 5 and 20 PSI and still ran tolerably!!


Good point. You'd notice a bad fuel pump when going up a nice steep grade or under load. I've seen GMC check engine lights come on, cleared codes and the light didn't come on again. It's not the norm, it's the exception. So yes it could be a fluke,,,,,,,,but keep your eyes open, and don't run the tank too low.

 

[ksJoe]

Originally Posted By: TallPaul
Made it another 640 miles and so far the light has not come back on. So not I have 1240 miles home.


Are you saying you are still 1240 miles from home?

If I was you, I'd have a spare pump in the glove box. It would be a pain to change on the side of the road, but I'd like to have that option if it died in the middle of nowhere.

 

[TallPaul]

I don't know why I always type NOT when I mean to type NOW. Yeah, have 1240 miles to go, but I am down here for a week, so could have it R&R'd here (Lakeland FL). The mech said the pump is pretty loud. It is, but I thought that was normal and it's been that way since I got the motorhome at 9700 miles. I might have had it changed out yesterday, but the only option was AZ or Rileys, whatever, the mech said those are not very good, all made in same place, and can go in 100 miles or 6 months. He said get the dealer pump, but I wonder if this one is bad at 21,000 miles, what is so good about the dealer pump?

Spare is not a bad idea, so long is it fits, else I am stuck with wrong pump. Sometimes there are running changes as I experenced with my old motorhome in Golden Co as the guy had to run to Ft. Collins on Sat am to get a wiring adapter.

 

[mechtech2]

A change in the sound of the pump is an indicator.
Sometimes the seals are bad. GM had problems with 'O' rings.
How about a real pressure test?

 

[ksJoe]

Originally Posted By: mechtech2
A change in the sound of the pump is an indicator.
Sometimes the seals are bad. GM had problems with 'O' rings.


Speaking of that... I was changing the oil yesterday in my wife's 03 Vue (3.0 liter v6, ~104k miles). I heard what I thought was an exhaust leak, so I crawled under the back end and it was clearly coming from the fuel tank. It sounded like a hiss or fluid sound. Should I go ahead and replace the pump?

 

[GMBoy]

Originally Posted By: TallPaul
So I left Detroit Thursday am (-10F) and headed for Florida. About 300 miles along, the "Service Engine Soon" light came on. Drove another 300 miles and had the codes pulled the next morning. They said the codes were low fuel pressure, and said it was putting out about 22 psi instead of what it should be around 40+. This was from the scanner, they did not put a fuel pressure gauge on it. Also, I never noticed any driveability problems, seemed to have full power all the way, so if there was low pressure it was hardly noticible in the performance.

Shop turned off the light and said not to run below half a tank (this is a motorhome with 55 gallon tank) I consistently filled up at half on the gauge and it took about 30 gallons each time. Made it another 640 miles and so far the light has not come back on. So not I have 1240 miles home.

So does the half tank of fuel cool the pump by the fact that the pump is at least partly submerged in the fuel, or does it cool it by the fact of the fuel flowing through it and too low of fuel allows the fuel to heat up too much?

Also for any tech people, it's a 2000 Chevy cutaway van chassis with 454 V8 (7.4L), it's a one ton, 3500 series, with 21,000 miles on it. The actual codes were (as the tech wrote it on a paper):

FUEL TRIM
BANK SENSOR
BANK 1 2

Anyway, looks like I am good if I keep it no less than half a tank. Once back in Detroit area and in the spring when the weather warms, I'll run it low and see if it will throw more codes. Hate to change out the fuel pump if this was either

1) a fluke that won't likely happen again, or

2) a false code (is that possible?).

Thanks,




It never amazes me what people will tell you. Was this autozone or something??

The scan tool (atleast for your model and year) WILL NOT tell you the fuel pressure-you need to hook up to the schrader valve and read it with a gauge. Those terms they gavce you (fuel trim, bank 1,2, bank sensor) are NOT codes but variable that you can view on the tool. You need the P number code to get the diagnostics started, or atleast what the values were. Based on what it COULD be - sounds like perhaps you were running lean on both banks which MAY be a fuel pump issue or just a fuel filter. Then again, could be fuel injectors. See - you need all the info to get started. Being a fellow RV'er I know the last thing you want to do is get on the road not knowing for sure if you'll make it. In any event, get the codes pulled again - there should be history codes atleast, and let us know. I will pull up the GM service manual and help you from there.

Take care now!

 

[TallPaul]

Yeah, I kind of thought that fishy, as if there was a fuel pressure gauge built into the vehicle. Whatever, I would think he looked up those variables to get the low pressure. P Number Code? What is that?

I have to think that with the low mileage, it should not have injector issues and I changed the filter prob within 10,000 miles, maybe less. I'll have to check. But the unit did sit around a lot for several years after the original owner's divorce until it was sold/traded to the dealer I bought from. I have run Schaeffer's Neutra 131 in it a few times and actually had it in the last tankfull before the light came on. Maybe there were deposits from the sitting around and the Neutra just loosened it up enough to get a temporary condition that threw the code.

Shops! Can't trust 99 in 100 of them if even that. This was a diesel/automotive repair shop that also has towing and three road service trucks. Would think they know what they are doing. I may call them back tomorrow and ask what excactly the codes were.

Thanks

 

[The_Jeff]

IDK my new fords but if this is a returnless fuel system there may well be a pressure sensor at the fuel rail telling the in-tank pump how hard to push.

 

[GMBoy]

TallPaul -

The P code is the Powertrain code that the PCM set. All codes for OBD2 are preceded by a letter. P=powertrain, B=body, C=chassis, etc.


Good point, eljefino but that is a return system.

 

[TallPaul]

My regular mechanic thought that it maybe could read pressure, depending on the model or year. Anyway, suspect it's a fluke, maybe an aftereffect of getting it cleaned up after the years of sitting. Also said that it's the fuel flowing through the pump that cools it, not really that the pump is sitting in a pool, so I can probably go down to 1/4 tank, which would be 15 gallons remaining. When they tell you not to go below a half tank, it's usually a car with a 16 or 20 gallon tank, so 15 gallons should be plenty.

Shop that did the work agreed when I called and said that what he gave me were not codes but parameters. Maybe I didn't hear them right at the time, anyway, they were certain of the codes being for low fuel pressure.

Also, I changed the fuel filter 6000 miles ago (15 months) with a Purolator filter.

Anyway, I will drive it as is for not hoping it's a fluke and take my chances. Your taking your chances anytime you go out on the road, there is so much can go wrong with any of these vehicles, not like a Model T what you can fix on the side of the road with baling wire and a pair of pliers.

 

[MrCritical]

Listen to GMBoy. The code reader cannot read fuel pressure.

 

[TallPaul]

Would make sense to me that it would read a lean condition, not pressure. Either way, I am cautiously treating it as a fluke for now.

 

[StevieC]

Sometimes ECM's do weird stuff... My mothers Kia set the check-engine light. I used my dads scan-tool and it gave me the P-Code. I Google-d it and it said that the code was because the ECM didn't successfully complete the self check. I cleared the code and she has driven it 75,000km since, never came back...

Who knows!

 

[another Todd]

My Ford motorhome had a weak fuel pump, and coming over the mountains from the desert it would vapor lock while running and die. After about a 30-45 minute cool down it would run again. Replacing the pump solved it. BTW this was a common problem for a few years of that chassis, as was a low volume power steering pump which caused an issue on the highway.

 

[GMBoy]

Originally Posted By: another Todd
My Ford motorhome had a weak fuel pump, and coming over the mountains from the desert it would vapor lock while running and die. After about a 30-45 minute cool down it would run again. Replacing the pump solved it. BTW this was a common problem for a few years of that chassis, as was a low volume power steering pump which caused an issue on the highway.



My dad has a 1996 Newmar RV built on the ford chassis - had the same problems you speak of.

 

[TallPaul]

Originally Posted By: GMBoy
Originally Posted By: another Todd
My Ford motorhome had a weak fuel pump, and coming over the mountains from the desert it would vapor lock while running and die. After about a 30-45 minute cool down it would run again. Replacing the pump solved it. BTW this was a common problem for a few years of that chassis, as was a low volume power steering pump which caused an issue on the highway.



My dad has a 1996 Newmar RV built on the ford chassis - had the same problems you speak of.


I had a '97 Ford F53 Chassis Class A with about 40,000 miles on it and 2 years ago the fuel pump went bad, couldn't get up the mountains west out of Denver, was laid up in Golden two days getting the pump R&Rd, cost $750 to replace including a run to Ft Collins Sat am for a updated wiring connector that the local Ford Dealer didn't sell me with the pump, the pump was about $360 so the whole deal was over $1100. Almost nobody wanted to or could drop the 85 gal tank. Should have an access hatch in basement compartment to get at pump.

 

[another Todd]

Mine is a 1996 with the F53 chassis, 460 cu in.

 

[TallPaul]

Yeah, I had the 460 V8.

Well, I ran the Chevy motorhome 2200 miles since the light was turned off and it still hasn't thrown another code. Have run down to 15 gallons in tank. I don't think it's a problem.