Your thinking is correct,the pressure can be fine around town but under load a diff story,also go one better,the fuel pump can show 70 when cold but after running few hrs can show alot lower from a worn pump, alot put a blue spring in and ck cold and it shows 65-70lbs and take the gauge off and forget about it untill probs arise and ck pressures again cold,shows good but dont recheck after running few hrs to know true pressure.

 

Thanks for the reassurance that my theory holds water. I will have a pressure gauge on the truck hopefully some time today. What pressures should I be looking for at idle and under load? I'm trying to see if I can get one of our shop techs to get the gauge on the truck during the workday so I can go for a lunchtime road test. If this thing ends up needing a fuel pump I'd like to track it down today and install it after work tonight.

 

Blue spring should yield 65-70lbs

 

Well gentlemen, it is definitely fuel pressure. Got the gauge hooked up just a short time ago and it's only hitting about 38 psi. Under load it drops a few pounds from there so I am rectifying this before any more driving.

With new filters installed Monday night and a blue spring (has been in there for years), I suppose this means a fuel pump but is there anything I need to check in regards to the regulator? I just don't want to make a wrong turn here.

 

Pull the regulator out and ck the rubber seal on the plunger, look at the spring to see if warped, put it back together if all looks good and reck pressure again,if low get a pump asembley so you have the updated system.

 

 

Being its a local big box store,you will get a lifetime warranty good anyplace,keep a pressure gauge on truck always,see it get low,replace pump under warranty, no shipping no waiting no stress.

 

Good point- should have considered that when I replaced it the first time 90,000 miles ago. Went ahead and ordered the Napa/Carter pump and it will be delivered here shortly. Thanks for pointing out the warranty aspect- nice to know that this will be the last time I pay for a fuel pump.

I will report back after the pump installation with results.

 

Glad to hear you're on the right track.

I would advise three complete priming cycles(let the pump build pressure each time and shut off) once it's back together before you start it.
It's also a good time to check for leaks since you don't have the danger of a live truck.

I would dare say this might have been, or at least contributed to the injector issues originally.......cold weather may have also been a factor that possibly caused the pump to get that weak if you had some restriction at the filter, even though it was not a bad blockage(if one acutally existed)

 

The "Carter" pump is most likely a private labeled Racor since Racor holds all the patents. But just because you replaced that spring before doesn't mean you don't have spring/regulator issues.

 

 

UPDATE- I'm in the shop at work and just got done installing the new fuel pump and unfortunately the problem is still here. Fuel pressure didn't improve at all. After running the truck for a few minutes to see if it just needed to purge more air out of the system, I noticed diesel dripping from under the vehicle. A closer inspection finds that the fuel pressure regulator cover appears to be leaking. I don't believe this was happening before the new pump, but who knows. Maybe it was slightly leaking undetected before but the new pump is bringing about this issue? For a while there was a pretty steady drip under the truck and then over time it seemed to slow down but when I checked the underside of that cover with my finger there is definitely diesel there. Even after cleaning it off.

For a while I was noticing the fuel pressure would start at 34 and then climb to about 37 or 38 and then tick right back down to 34 and climb back up to 37 or 38 again and then check back down. Then it stopped doing that. What the hell is going on here? This has been a terrible couple of weeks with this truck and I'm running out of patience and funds. There's nothing left that could be affecting fuel pressure except the regulator, correct? As I mentioned earlier in this thread this truck does have the blue spring upgrade but it has been in the truck for God knows how long now – probably 10 years. Is something going on behind that cover? I know I at least need to replace the O-ring on the cover but I'm sure you can't get that by itself so am I buying another complete blue spring kit?

 

Well,if the fuel pressure regulator cover is leaking id think you need to pull it off and ck it before even buying a pump as the seal on the plunger can be bad,the spring be bad,but now you know you got a good pump so leak needs fixed then go from there.

 

You need to step back.

A. Is the fuel gauge reading correctly? Check it's calibration against another gauge or known pressure source.

B. Pull the reg and make sure it's assembled correctly, seals haven't been screwed, and maybe replace it with new.

C. If neither of the two then pull the supply line from the tank off the HFCM and substitude the line with 3/8" hose feeding from a can or tank of fuel. Engine doesn't have to be started, you just need the 20 seconds of pump running. If pressure's up, then you need to lookin the tank.

 

After re-reading my post I believe you may have gotten the impression that I was saying that the regulator cover was leaking prior to replacing the fuel pump and that is not the case. What I was trying to say is that to my knowledge it was not leaking prior to replacing this fuel pump.