87 2.9 low fuel pressure KOEO

Making some headway here! I've got 4psi fuel pressure with key on engine off.It's supposed to be 40psi.When it's running i'm getting 31psi;the book calls for a 3-10psi drop when running from the 40psi KOEO reading so 31psi is within spec.
(The book doesn't address this situation in it's troubleshooting chart or identify which pump it's talking about)
Is this an indication of a bad external fuel pump or in-tank? or what else?

You should have 35-45 psi KOEOff or Engine idling. 31 psi idling and probably only 28 or so at higher rpms would make it run too lean

A 3 psi KOEO could indicate:
< 0.5 volt difference from batt voltage where the power lead connects to the pump poor pump ground at chassis

After ruling out these items, you could conclude a faulty pump

Replace filter too.

Personally, I would do these procedures to confirm:
A flow test of the pump: should put out a little over 2 liters/minute (bad pump or restricted filter)
Recheck PSI without vacuum line off of regulator and vac line plugged...rev engine...pressure should not drop more than 5 psi (could also indicate a bad regulator)

OK,thats helps a bunch!Will dig into it this morning.

Changed the in-line pump which brought the KOEO pressure up to 20psi from 4psi.Running pressure came up 1psi to 32psi;rev the engine and pressure is steady at 32.Removed the vac from regulator and pressure goes to 40 and holds steady when reving the engine.Engine runs rough regardless..Apparently the regulators bad but i'm getting a fuel smell in the tank area though I can see no leak.Suspect leak is keeping the system from pressurizing.Need to drop the tank to find out whats going on there...

wingzam said:

Changed the in-line pump which brought the KOEO pressure up to 20psi from 4psi.Running pressure came up 1psi to 32psi;rev the engine and pressure is steady at 32.Removed the vac from regulator and pressure goes to 40 and holds steady when reving the engine.Engine runs rough regardless..Apparently the regulators bad but i'm getting a fuel smell in the tank area though I can see no leak.Suspect leak is keeping the system from pressurizing.Need to drop the tank to find out whats going on there...

Click to expand...

SOunds good for the fuel pressure.

as far as the potential leak....you might have better luck removing the bed...6bolts and some wires to watch for & fill neck tube...and you can see the whole top....almost lighter too 2 meduim sized guys can do it.

Could Ethanol be screwing up the fuel system??

IMenriched said:

SOunds good for the fuel pressure.

as far as the potential leak....you might have better luck removing the bed...6bolts and some wires to watch for & fill neck tube...and you can see the whole top....almost lighter too 2 meduim sized guys can do it.

Click to expand...

Thanks for that tip!!!!! Will also aid in cleaning up the undercarriage of years of greasy grunge - I sure didn't relish the idea of getting under there with a high pressure gun!!

wingzam said:

Thanks for that tip!!!!! Will also aid in cleaning up the undercarriage of years of greasy grunge - I sure didn't relish the idea of getting under there with a high pressure gun!!

Click to expand...

If i remember correctly from someone else...you may want to pay close attention to the lines where it enters and exits the tank...might have a bad spot there.

and Yes, I agree crawling under there is not anything close to enjoyable.

Even if you got things good and clean, odds are good that the straps would break, unless tank has been recently removed from a prior repair?

Worse case....you see that the tanks still needs to come out. It will be A LOT easier with the bed off, 1) you can see 2)that anybody helping has a better line perpective too. 3)tons more room to work....did i mention you can see, something about handling a relatively low flash point container in natural light is whole bunch better. IMO

wingzam said:

Changed the in-line pump which brought the KOEO pressure up to 20psi from 4psi.Running pressure came up 1psi to 32psi;rev the engine and pressure is steady at 32.Removed the vac from regulator and pressure goes to 40 and holds steady when reving the engine.Engine runs rough regardless..Apparently the regulators bad but i'm getting a fuel smell in the tank area though I can see no leak.Suspect leak is keeping the system from pressurizing.Need to drop the tank to find out whats going on there...

Click to expand...

Bed off.Found the rubber hose that connects the vent to the hard plastic vent line had softened up and let the line come loose.Back to the pressure regulator unless someone has a better idea.The filters have been changed,one of the fuel lines I pulled was clean.Also,though this truck hesitates/bucks/whatever at mid RPM,it gets up and hauls to 90mph with no problem.

As for quality of regulators:I can get an Echlin at NAPA for $27,Sorensen at Autozone for $39,BWD for $84 at Advance,and a BWD from O'Reilly's for $64.Guy at NAPA says he's never heard of any problems with the $27 cheapie but you gotta be suspicious!""Does anyone have any experience with these?""Of course I tend toward the more expensive on something like this,but could really use a savings about now,and as I said in the post above - when I pulled and capped the regulator vac line I got 40psi and the thing actually ran alittle worse....so am apprehensive about the regulator fixing the problem....then it's more money down the drain......

Your regulator sounds like it is functioning reasonably well albeit a tad low on running pressure. However you say it runs worse when the vacuum line is disconnected and when pressure increases to 40psi. This to me indicates an already 'too rich' condition. Typically by pulling the vacuum line off of the regulator, idle will increase by about 200 or so rpm with the increased regulator pressure and additional fuel through the injectors, but should not make it idle rougher.

Have you cleaned and measured voltage at the MAF sensor and cleaned the IAC valve yet? One last item to measure would be the voltage at the throttle sensor. Then pull a spark plug or two and check for any carbon buildup. Bear in mind if there is carbon and depending how long you have been driving it like this, the oxygen sensor may be contaminated which is a second problem caused by another unknown reason for the 'running rich' condition.

Forgot to ask if you have cleaned out the throttle body plate and bore yet?

Just a couple of weeks ago had to replace a fuel injector (replaced them all cause I got a great deal on ebay for 6 refurbished ones).Removing the rail and upper manifold found the intake to be surprizingly clean so no reason to suspect a gummy IAC which is nearly new (can check anyway).Also replaced the plugs which showed a lean condition (of course).This corrected a rough starting problem,but the hesitation remained.It had worsened a little since then.Fixing the loose vent line has reduced the hesitation so am back to same running condition after I changed the O2 sensors about a year ago for causing a rich running condition.This vehicle has the MAP sensor I think.It can't be cleaned;it's a sealed component on the firewall (have another I can plug in).Throttle blades are clean,throttle positioning sensor is new.I had read the voltage but a friend told me to get an accurate reading it should be read with an osciloscope.Spent $30 instead of taking it to a mechanic - which twice has not proved very successfull!Cap and wires are new...This thing has been one monster since I got it.Won't even go into it except to relate one thing that kind of charaterizes the whole thing:just last weak I replaced the catalytic converter because the exhaust was noxious so figure my problem is a clogged cat.Spend two hundred dollars only to find the cat had been hollowed out by a previous owner (My previous suspicion was correct thinking it accelerated too well to be a clogged cat).And on and on and on it has gone with this vehicle!!My financial situation is such that I can't get into a better ride and i'm in a smaller town where there just ain't much to choose from.And buying another cheap truck is just asking for another "Dump money" situation,so I find myself in this pathetic conundrum of working on a vehicle that just WONT be fixed,but seems always close to being fixed - if I just dump a little more money into it...won't even tell you what i've got into this piece of crap which I really shouldn't have bought in the first place - but needed a small truck that was good on gas -hahaha!!!

BTW,already bought another fuel regulator and will put it on tomorrow.When I tested the fuel pressure I had yet to find the loose vent line so am hoping this was the cause of the poor running at 40psi with the regulator vac line disconnected and capped.In fact,since I love punishment so much I think i'll go change the regulator now while the mosquitos are thick and hungry - and I won't use any repellant!Oh Ya!! More!!!!!!!!!!

Damn,it's raining.No mosquitos out......

Update:Changed out regulator - no change.Will run pressure checks,etc.. tomorrow.So far $500+,four seperate problems found and fixed.It's still on the road and thats better than nothing!

Did you put in the other MAP sensor yet?