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I have a fuel pressure ?

I hear you but I need to stop somewhere and drive it for awhile instead of being under it every week. After vaca. I'll start playin and do the wants since the have to dos will be done. Oh yeah and the money thing to. You know A turbo will be in the cysrtal ball after the chip exh ftb I could go on all night. I feel like I'm building my gs400 all over again. It never ends . I need more more more.
 
Forget them 80mph runs, its the 120mph runs that really suck down the fuel. With the ATT the 120mph above 3000rpm engine is still happy humming along nicely. With the GM4 you can tell its working too hard.

In the stickies there is an LP/OPS troubelshooting thread that is a very good read, especially for a seasoned mechanic that will probably grasp it real quick.

http://www.thetruckstop.us/forum/showthread.php?t=6872

I put in a lot of the OBD1 specific things related to 92-95 trucks in posts 23-24. Low pressure could be low voltage through the OPS, which you can check at the DLC port pins, clogged fuel tank sock, clog in the lines or dying lift pump.
 
I did the exh. today and wow had I known the diff. it makes I would have done that when I got the truck. I haven't towed yet but the egts seemed to have dropped between1/200F. the truck spools faster and has more power now, and since it only took an hour to do d/p and c/o I looked into the fuel issues. Would you believe that it has the original l/p. The guy I bought it from said the only thing he replaced on this truck was fsd and now I believe it. even the t-stat looked orig. Now I'm going to chip it and wmi it and hopefully chill for awhile and just drive it.
 
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I verified l/p pressure and it's at 8lbs. at the l/p outlet. I guess I'm going to have to take off the ffm,unless there is something I can do like blow pressurized air thruogh the water bleed valve. Does the fuel have a seperate supply feed to the I/p and the water bleed out of the ffm. Can I take the hose off I/p and check pressure there or should I just take the ffm off and look for crap in there or something more specific.
 
Get right in there... take upper and lower intakes off, and remove the FFM.

This gives you a good view of all your fuel lines. replace everything is my recommendation.

Great time to put a T in front of the IP for a fuel pressure gauge, or at least a convenient test port for now. 18" hose or so out of the valley to a safe spot.

Pesky OBD1 OPS will never get easier to change at this point.

I was just in there and put PMDCABLE.COM's OPS switch and extender just because it was easy.

I also replaced both feed and return lines.

I'd get 10' of 3/8ths fuel line, 10' of 5/16 (for the return), and if your factory get a few feet of the 1/4 inch as thats all a non FTB'd FFM outputs. It could be dry and crappy, and may be hard to find diesel fuel hose on a weekend.

You can cut the factory lines where they are rusted and crappy off and slide the rubber hose over and double or triple hoseclamp it. Not a high pressure system here (unfortunately ) :)

Go in prepared and come out a winner. Don't forget a few bags of HOse clamps. Home Depot Sells nice SS ones BTW. I just realized this.

I will never use a non stainless hoseclamp again.
 
The filter manager has both outputs, one post filter to the IP and one prefilter to the drain fitting. There have been instances of people finding them backwards which would be bad.
 
All hoses are routed under the intakes to the IP. It would be a super bitch to even try to do it with the intakes on. Plus you'd be blind. You'll get out of the repair what you put into it.

Don't forget new gaskets... upper and lowers.

There will be no coolant mess BTW. None.
 
Thanks thats kinda what i expected. Was hoping against it but I guess I knew in my gut the truth in this matter, more work less play makes it like any other day. Well if I put it off will it do any damage or is the water seperator likely clogged and fuel making it to I/p fine because the truck runs fine even though I get only dribble of fuel out the ff/bleed and nothing out of the petcock on t-stat or should this be taken care of before something serious IE; expensive happens
 
You need to resolve the fuel pressure issue ASAP. Where did you have 8psi pressure, at the LP output under the truck? Important to know how you powered it too, and you get only a dribble at drain line when powering it the same way.

Taking off the intake is a clean job, not hard, but only PITA are the injector lines, and you dont want to bend them much at all. If you remove the FFM and just pull new lines through with old lines, then its not so hard. Old lines are premolded though to fit just right. A new line you would need a way to keep it from kinking when turning it 180 degrees back into the IP. Thats why with the FTB mod you use a 90-150 degree metal hose end.

Would you replace with new 1/4" lines for now to match stock fitting nipples and in the future upgrade to 3/8" with the FTB mod. FTB fittings can be bought anywhere. Walking J sells nice steel one for the upper IP that I totally recommend. Its a steel 7/16-20 Oring fitting adaptor to -6AN male. And you use a 90 or 120 or 150 degree hose end to convert the 3/8" line coming up from intake to -6AN (aka 3/8" JIC)
 
Under the truck L/p outlet powered with truck running. What a mess. the p/g line popped off and I went to shut the truck off and the engine was still cold so o/p stayed high and didn't shut off until about 10/15 sec. later. needless to say about a 1/2 gal of fuel on the floor. Dribble was at the ff bleed.
 
You should take whole FFM out and take it apart and clean, new filter. Also disconnect the LP output and blow out the line from FFM to Lift Pump with some high pressure air. Some people find big chunks in there somehow. When you take it apart you will find a fuel heater coil inside the center shaft. I just removed that to lose restriction.

You may also find that the LP is able to make pressure but not flow, so it dead heads at the restriction of the FFM and cant actually push fuel. May be time for new LP and OPS relay mod if not done.
 
How does ops mod help if my ops is working. Everything on this truck that I replaced is orig. except the pmd. I'm a firm believer of if it aint broke leave it alone. And with 213.000 on it, it must be the truck from heaven because I've only replaced the t-stat and h-balancer and eliminated the v/p. I don't mind doing mods for perf. and reliability but not until orig part fails. But if I'm going to take the intake off and be in there and check all the fuel lines I will do ops if that is something that could leave me DOA somewhere.
 
The OPS may not actually be working 100% and could be limiting power to your LP. Its a lot like what happens to some ignition switch contacts when they get charred/burned/corroded. It will pass a voltage potential but at a high resistance and limit the current through. And with those ignition switch contacts it will start the vehicle but stall it or take a few key turns to find a decent continuity. The internal OPS contacts are not rated for 2-3 amps that it takes to power the LP so they die fast, usually within a year.

And the OPS is a common maintenance item if you have not performed the relay modification. Also consider it preventitive maintenance. A weak or dead LP for any reason will kill an IP pretty quick. Even though the IP can function by sucking the fuel itself, it wears it quickly. The OPS relay mod is a $10 one time mod that will save you a lot of money and frustration in the future.

Youve likely found your problem as to why it starts overheating and doing crappy going uphill at high speed. The OPS is just like the PMD, a bad design by the factory that MUST be corrected for a reliable truck. And this only applies to pre-OBDII trucks, because GM realized their mistake and had the PCM control the regualar automotive relay to run the LP in OBDII trucks, even though they left the OPS there, it is just redundant power supply that will also prime lines post shutdown. OBDII also put in a DTC when the PCM gets no power feedback on the LP circuit. Thats how important they found out a functioning LP is.
 
Your factory lines may be clogged up between FFM and LP too, I recommend just cutting the old ones out and rubber length up to a nice solid piece close to the LP.

Before I did this I had marginal volume out of Water drain, I remember from another thread. Now i'm spewing real good out of the bleeder.

All that should be the same flow before FTB or not, in fact, it theoretically should have speweed MORE before FTB as the restriction would raise pressure in my FLT MGR Faster. But it didn't.

I cut them right out (sawzall on that damn clip right behind FFM) and pulled em out. Cleaned it right up in there. Cost next to nothing.
 
Cool I hate to replace the lines. everything on this truck is good even the original oil lines don't leak. every nut or bolt I've touched comes right off. I love the south no rust. far cry from mass. I lived there for 35 years and never had it this easy working on a vehicle.
 
Mine were crap so it was a no brainer... Burning oil did this with his and carb cleaner and said a bunch of chunks and crap came out... I'd spray a whole can through there then air... As good as it gets.

While FFM is out, take it apart, and chances are the O-Rings are ready for replacement. There are 2 of them. Bring them somewhere to match em up. Hydraulic places will have VITON rings, supposedly the best. I got 2 sets of Viton rings for 3 bux. Cheap.

And take it from there...
 
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