I tried searching posts and got some answers but I am looking for more definitive ones. I have a 97 Ranger 4x4, 4.0L, A4LD, 68k mi. with P0171 and P0174 codes, lean fuel mixture banks 1 and 2. The truck will rev up and down from 500-1000 RPM when Im rolling in Drive. When I accelerate, its fine, but when I let off the gas and roll it starts reving again causing the truck to shake. I replaced plugs and wires before the codes (1-2 months ago). After the codes came I replaced the fuel filler neck (not because of the codes), cleaned the air filter, cleaned MAF, changed fuel filter, and checked fuel pressure which was at 29psi so I replaced the fuel pump.
Is there any common causes for this? Cures? Thanks for any help.

MattF

 

Welcome to FTE!!

I would suspect the lower intake gasket leak. See the link on this topic in the tech info thread at the top of this forum.

 

My 98 4.0L is doing the same thing. I tried looking for a simple vacuum line leak, but I can't seem to find any. I am starting to think I should just do the gaskets, so I started reading Rockledge's writeup and his thread.

<a href="https://www.ford-trucks.com/forums/archive/index.php/t-232373-Coolant%20Loss%20-%204.0L%20OHV%20Lower%20Intake%20Gasket">Coolant Loss - 4.0L OHV Lower Intake Gasket</a>

1) Is this also a known problem on the 98 4.0L? I noticed that Rockledge mentioned that the Fuel Supply Manifold Gasket can go bad on the 1997 and get drawn into the the intake manifold runners causing a vacuum leak and the lean codes. Could my 98 have this same issue or was this addressed by the time the 98's came out? I guess it is worth checking if I get it all out.
2) Is there anything else that I should replace while I'm doing the Upper and Lower intake and valve cover gaskets?

-Jim

 

Im kinda thinking about changing the IAC and TPS before I dig into the gaskets. Is it worth it to try this or am I delaying the inevitable?

 

A vacuum/air leak, a misbehaving PCV system, leaky intake gaskets, even an exhaust leak, all could cause an engine to run lean.

A dirty MAF can cause an engine to run lean. See: Cleaning the MAF sensor.

Some of the 1997 4.0L's had problems with the fuel supply manifold gasket (not real hard to replace, btw):

Article No. 98-6-8

LIGHT TRUCK: 1997 AEROSTAR, RANGER 4.0L ENGINES ONLY

ISSUE:
A rough idle, stalling at an idle and/or Diagnostic Trouble Codes (DTCs) P0171, P0174, P1131, and/or P1151 may be stored in memory on some vehicles with a 4.0L engine. This may be caused by the gasket located between the fuel rail and lower intake manifold losing its compressive loading and becoming drawn into the intake manifold runners resulting in a vacuum leak.

ACTION:
Replace the fuel rail-to-intake manifold paper gasket with a revised gasket.

....

 

I haven't found a vacuum/air leak. I don't notice an exhaust leak either. Every time I take the MAF off, it looks as clean as a whistle. I guess I can try replacing the PCV grommet and valve first as they are cheap.

 

I replaced the PCV valve and grommet, but it doesn't seem to have improved the situation. My gas mileage is also way down (about 14mpg, usually 19mpg), I assume from the computer adjusting to rich.

Will shops that have a smoke machine (evap tester) diagnose a leak? How much should it run to have hook up their machine and blow smoke in my tubes? I found my EVAP test port over near the battery, but I don't have a smoke machine.

 

Jim, I can't really help you out on your questions, I would think you probably have to call around and see what kind of rate quotes you get. I'd say you should probably be looking for the kind of shops that hold themselves out as particularly proficient in diagnostics (as opposed to your local corner garage, who may be excellent at wrenching, but not as up-to-date on the latest diagnostic processes and equipment).

I'd be interested to hear how it turns out, if/when you have the smoke test done.

 

Wow! dkthree, your post could have been written by me, except I bought the fuel filter but haven't installed it yet. I also have not changed the pump. My problem also started shortly after installing new plugs. I was certain I must have knocked off a vacuum line, but apparently that is not the case. I guess it sounds like the fuel rail to intake gaskets are where we need to go next. I just don't understand why both banks showed up at the same time. Let me know if you get yours fixed first. I'll post my progress as well.

 

I found a buddy who works at a dealership who will go with me on a Saturday and hook my truck up to the smoke machine. So probably the first week of the new year, I'll have a definitive answer. Until then, he suggested replacing the Upper Intake Gasket (after he talked to some more experienced mechanics at the dealer). I figure they are cheap and easier to get to than the lower, so I may as well do them quick.

-Jim

 

Alright... I changed out my upper intake gaskets (aka "plenum" from what I was told) and that didn't do anything for me. The gaskets looked fine but I changed them anyway, I figured that was a start before I can get up the nerve to do the lowers. I also changed out my IAC, about $60 bucks from napa and that helped out a lot, but didn't fix it. The engine is much quiter now and I don't have the shaking during deceleration anymore. The last thing I am going to try is the TPS and if that doesn't work... then I'm probably going to the dealer.

 

Oh, and Rockledge, can you post some pictures of how to replace the fuel rail to intake manifold. Those pictures you post are awesome, I used them to pull my upper intake manifold. Thanks again.

 

Could you be having an EGR problem ?? Try removed the vacumm line from the top of the EGR valve. This will trip the Check Engine light, but note if the problem is still there ?? This is just a guess as I have a similar problem of surging and the EGR was the culprit.

 

I FIXED IT!!!!!! Well as far as I know anyway. It was the Fuel rail to intake manifold gasket (thanks Rockledge) that had been sucked into the intake. It took me about 3.5 hours from start to finish which was actually a half hour faster than it took me to change the upper intake manifold gaskets the first time. Oh yeah, and the dealer quoted me $590 to do this....Hah.

 

I think that my issue is fixed as well. I replaced the Upper Intake Gaskets last weekend and cleared the codes, but the P1000 was still present. This weekend, I finally read the Drive Cycle instructions and filled the gas tank up (it needs to be 1/2~3/4 full). The P1000 went away, the CEL did not come back, and my scanner showed no codes.

-Jim