Multiple problems!

[Happy Camper]

Hey everybody,

Looking for some advices here. I have a 98 B4000 with 270k on it so far.

In the last couple months, it started to act weirdly on cold startups (by cold I mean when it sat for a while because I don't think temperature matters...let me explain why!)

So the symptoms: when it sits for a while (like one night or more), the trucks starts after a bit more cranking than usual but when it starts, it doesn't get up in rpm and stumbles and does pretty much everything it shouldn't...After a couple seconds, something magic happens and it gets up to speed like a lion. Also, I had it sitting for a month once and I had to pour gas directly into on cylinder to get it going again (I was cranking and cranking and nothing happening so took off the plugs to find out they were still dry after excessive cranking).

I am away now but I soon as I return, I was planning to change fuel filter first and then what? This is where I need your opinion: I'm confident that a clogged filter can be the reason for the stumbling but to me, it doesn't explain why no fuel would be delivered at the engine after a long rest (seems like the fuel line gets kind of airlocked right?) To me, it looks more like a faulty fuel pump but at the same time, once I get it going, it runs fine even at high rpms/load so the fuel pump is somehow doing it's job...I'm lost! There must be something I miss...I also tried to leave the ignition on for at least 30 seconds before I attempt to start to give time to the fuel pump to prime the line, no change). I forgot to mention that the problem seems to be slowly increasing in severity.


Also (and it might be related), last winter, I had a P0174 (engine running lean on bank #1 or 2 (can't remember the number but it's on passenger side)). I investigated, cleaned MAF sensor, looked pretty darn hard for any vacuum leek (added cable ties to every hose just in case), etc. After a while of searching and questioning guys on forums, it came out that my last option was to replace the upper and lower intake gaskets (o-rings for the upper and gasket for lower). So there I was gone. Did the job even tough I wasn't sure it would solve my problem. Guess what: after I finished, everything was ok for a couple hundred clicks and then: boom! P-0174 again but with P0171 this time. So I had it from bad to worst! (Lean on both banks). Now, maybe I made a mistake but I can tell you I got everything back together in the specs and it's far from being my first time on that type of jobs and it would be my first time messing it up so I kind of doubt it...although I'm not saying it's impossible, it think it is very unlikely.

I forgot to mention that I do get terrible mileage and that I also have a P1309 at the same time which is: "Misfire Detection Monitor not enabled". Folks told me it could be my camshaft position sensor that is off timing but again, not sure. I don't really feel like trowing another shot in the dark so I ask for advices before I get my hands dirty and spend some money on parts.

I know it's a lot of problems that can interact together but I figured it would make it/them more interesting or impossible to solve!

Thanks for your ideas!

 

[Earl43P]

Prime the fuel system before each cold start, see if that helps.

Turn the key to Run, dash tests lights and the fuel pump runs for 2 seconds.
Turn key to Off. (waiting 30 sec is futile, 2 seconds then Off, you should HEAR the FP run)
Repeat, repeat, then crank the starter.

Lots of things can cause bad mpg.
Clean the MAF. Make sure the intake tube has no cracks/holes and is securely clamped.
O2 sensors (upstream) should be replaced at 60-100k miles, they get lazy.
Spark plugs, use Motorcraft double platinums.
Check the PCV tubing/elbow for the vacuum leak too.

Lastly, find someone (or buy) a scanner that can view live data (like a ScangageII).

Look at the fuel trims, O2 sensors, IAT, ECT, etc.

With the price of gas, it'd pay off even if you paid a tech for the live data/diagnosis.



HD40 CHECK CMP SENSOR OUTPUT

Diagnostic Trouble Code (DTC) P1309 indicates Misfire Detection Monitor is not enabled.


REPLACE CMP sensor. RESTORE vehicle. COMPLETE Misfire Monitor Repair Verification Drive Cycle. RERUN Quick Test .




HD40 CHECK CMP SENSOR OUTPUT

Diagnostic Trouble Code (DTC) P1309 indicates Misfire Detection Monitor is not enabled.

Breakout box installed, PCM disconnected.
Connect digital multimeter between PCM test pin 85 and test pins 51 or 103.
Bump engine in short burst with the starter without starting engine for at least 10 engine revolutions.
Does digital multimeter reading switch between low (less than 2.0 volts DC) and high (greater than 8.0 volts DC)?

Yes
Note: A Hall effect type CMP sensor that is installed out of synchronization will produce a DTC. VERIFY the correct installation by referring to the Powertrain/Engine Group in the Workshop Manual. If the CMP is installed properly, REPLACE PCM. RESTORE vehicle. RERUN Quick Test .

No
REPLACE CMP sensor. RESTORE vehicle. COMPLETE Misfire Monitor Repair Verification Drive Cycle


Realizing you have no break out box, but it does indicate a problem with the Cam sensor phasing or signal.

 

[RonD]

Yes, I would get(rent) a fuel pressure tester, you should have 60psi at the fuel rail for the injectors.
The computer has no way of knowing what the fuel pressure is, it expects 60psi so opens and closes injectors based on that pressure, if pressure is lower then not enough fuel comes in, if its higher then too much fuel comes in.

The 1998 models had the new "returnless" fuel system, so no FPR on the rail and the in tank fuel pump can have leaking issues, so loses pressure when it sits and also can't maintain 60psi when running.
They used a rubber connecting hose from pump to outlet and it can deteriorate and crack, this leaks pressure when pump is off but also lowers pressure when pump is on, as it is spraying fuel out of the leak inside the tank.

Pressure test will show if that's the case.

Low pressure makes for harder starts and "lean" condition while running.

Also check fuel line, a leak in the line from tank to engine will produce the same low pressure symptoms PLUS lower MPG which you mentioned.
Check/change fuel filter, that's a good place for a leak.

If there are no external leaks and you do need to check the pump then removing the bed is probably the best way to do that.

 

[Happy Camper]

Thank you guys,

I will start with easy things first. I will get a fuel pressure gauge and verify it. I'll keep posting results.

To be continued!