Thought I had it....

[mobilevet]

Well, I thought I had it. I found that the fuel lift pump was not working, figured out that it was the OPS (thanks to all that posted great info on that a week ago) and with the new OPS the fuel pump went back to pumping and making it's associated noises (those sure do make a bit of a racket).

Anyway, the original problem was that under a load (high speeds was my primary "load") the engine would feel like it would "miss". After fixing the fuel pump, I drove it on a couple of short trips around the county roads by the house (in case it laid down on me) and then to town (about 30 miles one way) and back a few times with no problems. Oh yeah, it also would give a SES code 18 when it "burped" and seemed to lose power.

Anyway (again), today I went to town and had to pick up a trailer (standard size tandem axle with max 1000# loaded on it)... well, you probably already guessed, got about 2 miles down the road with the trailer and the truck burped ("missed") and the SES light came on and I could do only about 55-60 mph the whole way home (no power). It really took a while for it to build up enough speed to even get the transmission to shift, even with my foot on the floor (no telling how much fuel I burned) and every hill knocked it back 10-15 mph trying to get up them.

Oh, yeah, I also noticed a "squeal" that wasn't there a day or two ago... haven't had time to track that one down - no way it could be the IP making a squeal is there???

So - I have already:

1.) Given the engine a good cleaning and inspected most all of the connectors and such. I did notice several of the wire protector sleeves were very brittle and I took them off and replaced them. I thought at one time that it might be the short wiring harness going to the optic sensor on the IP and took it off, it seemed fine, although it did look like the connectors were pretty rough from heat to the plastic and a couple of the clips that snap on when you plug it in were gone (previously broken I guess) - but according to the guy at SSDiesel if the problem is the wiring harness then you will have NO symptoms engine wise - just false codes (if this is not correct, please explain).

2.) I did all this checking and cleaning when I had it torn apart to do a cooling system upgrade to the high-flow dual Tstat system (which seems to work great, stays at 180 or lower on the temp gauge, the system from SSDiesel had everything I needed). I did have to re-route the fuel return line to get it to fit around the new Tstat manifold. But that seemed to go very well using a tube bender so that it did not kink - I just straightened it out and made a few new bends around the new manifold. I also made sure to make as few bends as possible and keep it nearly the same orientation as before as far as no new peaks or valleys.

3.) Other than that I sort of cleaned up the battery connections and tested the batteries - gave 13.5-14 volts each with the truck running. I took out the air snorkel - however I didn't know if I was supposed to leave the little short extension from the box that used to hook to the snorkel??? Just left it on for now. I also put on a new belt. The fuel filter was replaced the last time the motor did it's thing ("miss" and SES light come on) less than 200 miles ago.

Soooooo.... what do all the experts think?? One thing that I have not done is to check for air in the lines - do I need to do this??

This truck has two FSD's in it that are both (one in use) supposed to be good. Could this be an FSD problem? Should I try switching and see if that helps?

If it's the IP, then so be it - but I don't want to just jump to conclusions.

I know that there a bunch of questions here, sorry... thanks for any help.

[mobilevet]

Almost forgot, might not make a difference, but last time it did this, I basically didn't do anything except change the fuel filter (which was really not dirty looking) and let it sit a day or so and it seemed to run fine afterwards - until the next "miss/burp/whatever".... I was just wondering it this might point to some electrical issue versus a real mechanical problem with the pump's cam (code 18 is a Pump Cam Reference Pulse Error)???

[More Power]

Almost forgot, might not make a difference, but last time it did this, I basically didn't do anything except change the fuel filter (which was really not dirty looking) and let it sit a day or so and it seemed to run fine afterwards - until the next "miss/burp/whatever".... I was just wondering it this might point to some electrical issue versus a real mechanical problem with the pump's cam (code 18 is a Pump Cam Reference Pulse Error)???

If you get this code frequently, it means there might be a problem with the Optical Encoder Sensor or related wiring. The electrical connector is located at the very top of the pump. While some have replaced the sensor at home, this really requires a pump calibration to do it right.

The GM manuals indicate that air in the fuel can produce an OES error, because an air bubble can interfere with the optical aspect of reading through the coded disc. You can check for air by temporarily replacing the fuel return hose on the pump with a piece of clear vinyl tubing, then running the engine and looking for bubbles.

http://www.thedieselpageforums.com/photopost/data/500/OES.JPG

Jim

[Chief919]

It does kind of sound like you are sucking air.

Does the problem occur more when you have a lower fuel level? If so, I would suspect the pickup in the tabk is sucking air. If not, I would suspect the fuel line between the tank and the lift pump.

[mobilevet]

Re: fuel level - not really, I have had it do it at all different fuel levels, although maybe the worst cases were at 1/2 tank or less on the gauge. This last time I had just put in 10 gallons (pushed the gauge just over 1/2 a tank) with a dash of fuel additive at the time of fueling.

Sounds like an air check is worth the time and effort...

[redbird2]

I'm think you need to check the lines relly close from the tank to the primer pump, I would agree with the others it is sucking air. I recently had one that would run fine above 3/4 tank below all kinds of performance problems hard start sometimes. Finally one day the owners 9 year old made the remark moms trucks runs good after we stopded and got pizza. I dismissed the comment until later that night so I called and asked where they get there pizza and fuel at. the local mini mart has diesel and pizza place attached she told me she topped off there before she picked up the pizza.
So checked the fuel lines ok on top of the tank so I pulled the bed off truck faster than dropping tank pulled sender part way down the draw pipe there was a crack in it where a clip was tacked on so i pump almost all the fuel out of it droped in new sender put bed back on took for test drive ran great put fuel back in she has not had a second's problem since than. leave it to the 9 year old

i have also had to replace several sets of lines that where rusted so bad on top the tank that I could not get them apart with out breaking ot the fiiting broke off the top of the sender so if it cracked good place to suck air

good luck

[mobilevet]

Okay... I will check for the air. When my tractor sucks air (usually because of low fuel) it stumbles and carries on continuously until it bleeds it self back out and/or I fill up the tank for it - this truck is not doing that.... this situation is just one hard miss and then no power.... but I will check for air.

It doesn't sound as if anyone thinks this is simply a FSD/PMD problem... I assume that means if there is no air leak then I'm looking at replacing the IP?

thanks -

[mobilevet]

Okay.... I put a clear line on between the IP and the return line and saw NO bubbles. It cranked fine and I drove it up and down the road a few times, got up to 70 mph, it shifted fine and had normal power again. The only thing that I did between the incident and today was to let it sit parked until now (besides putting on the clear line).

any ideas???

[Warren96]

Is it cold where you are ? Fuel filters aren"t expensive change it again to be sure.

[mobilevet]

Actually is has been quite warm (60's and70's) here in Alabama....

This all seems so "electrical" to me, I just can't tell if it is an electrical component in the pump or some exterior electrical issue (PMD, wiring harness, etc). The current PMD was put on by the previous owner less than 10k miles ago (it is an SSDiesel Heat Sync kit, attached to the intake manifold). That seems like it is awfully new to be going out to me???

I guess I'm going to have to just put a new pump (with a new PMD) on it.... I hate part swapping without a real diagnosis.

[Warren96]

The last pump changed on mine was 90,000 miles ago, and that was because it was under warranty.It realy needed a PMD, but the dealer wouldn"t service the fuel injection system without removing the pump to send it to a stanadyne service center. I don"t know about your truck but on mine swapping pumps is a very expensive proposition out of warranty. Yes 10K on a pump is a little hard to believe. Can I ask one more question? How much fuel is in the tank? The less there is in the tank the harder it is for the lift pump to pull fuel from the tank. Been there done that!

[mobilevet]

This problem has occurred at all different fuel levels. First time I filled the truck and drove 300 miles and it occurred several times very mildly - almost couldn't notice, sort of just a hesitation instead of the hard miss, other times the fuel gauge showed 1/2 tank or greater. This last time the fuel gauge showed just a little under 1/2 tank and then on top of that I had just put 10 gallons in.

For clarification, to my knowledge there has never been a new PUMP put on, only new PMD's. First time by second owner at approximately 200k - he put it on the new one on the firewall with a heat sink and a small electric fan blowing on it. Then about 30k miles later the previous owner (to me) put another one on with heat sink mounted to the intake manifold - This is the one that is currently in use.... or at least was until I swapped it back to the one on the firewall yesterday. According to the previous owner (#3 - I'm #4) he only got the new PMD so that the older one would be a "back up"...right now the one on the firewall worked well enough for me to run around the neighborhood, but I haven't tried it out on the highway for any significant distance as of yet.

Still seems strange that the #3 PMD (with less than 10k on it) would be acting up..... thus my concern about the pump itself with 230k+ on it.

Everyone completely confused now!

[93GMCSierra]

Heat is what kills them so if the one mounted on the intake was getting too hot it could easily go out prematurely.

[cmark66]

I have a 95 Yukon and have replaced the standyne and fuel pp, mine started acting up again, run, die, start ,run, die so on, It happened at 1/2 tank and less, I figured a fuel Pp again, put in clear line with no bubbles, had great fuel flow and pressure, when I got to 1/2 tank again it died, this time on the lift noticed fuel running down the tank, found a crack on top of the tank and after thinking back to the last refill I didn't hear a vacuum noise when I removed the fuel cap. simple thing but I jumped right to the electronics first.