'98 ranger running lean no vac leaks MAF or Fuel pump?

[Bajabronco]

I have a new to me 1998 ranger 4x4 ex-cab. 4.0l/5 spd manual. 250,000 miles on it. PO installed a k&n cold air intake and an aftermarket exhaust. He also had a hypertech programmer running when I bought it.

Check engine light was on when i bought it, pulled the codes: 171 and 174 (lean on banks 1 and 2) cleared them and ran through a tank with the truck still re-programmed. then the engine light popped for me, same codes, just wanted to check. Cleared again, checked vacuum lines and connections, cleaned the engine (pressure washer) and programmed the truck back to stock. Ran fine with no codes for 500-600 miles and 2-3 tanks of regular. Yesterday the light came on again, though this time it only read bank 1 lean, not bank 2 aswell. Today i checked my mileage at 15.5 mpg driving very nice with 1/2 city, 1/2 freeway.
Also, in the last week or so it has been hard starting cold, 5ish seconds of cranking over the usual immediate start.

Today I checked again for vacuum leaks with starting fluid, idle was steady as a rock, I checked the vac lines and the upper intake gasket.

So now I am thinking either the MAF of the fuel pump, though the hard starting is having me lean towards the fuel pump. I haven't checked fuel pressure yet. All I have right now for a pressure gauge is a good compression tester, though i may have to buy a fuel pressure gauge. Do you just check this at the schrader valve on the fuel rail? I have read it should be up around 40 PSI.

I drove it very easy for the 500 miles of no light, that also leans me towards fuel pump if i was never demanding much from it.

I will try cycling the key for the next cold start a few times and see if it starts quicker aswell.


Any insight would be greatly appreciated, both the MAF and the FP are big ticket items for me and neither are returnable once installed.....I would hate to replace the wrong one.


Thank you.

 

[Bajabronco]

oh, also PO said the truck failed an emission test, not sure whether the light was on or off at the time.

 

[ForOffRoadDriving]

have you tried cleaning the MAF yet? you said it had a K&n and many times any excess oil used on these gets sucked into the engine and on its way it coats the MAF resulting in a false signal.

 

[Bajabronco]

Ok, cleaned the MAF, we'll see how that works. I didnt remove the sensor from the housing rather just removed the whole housing and sprayed it.

Could the MAF even be causing the hard starting? To me it still seems like fuel pump but I guess I will wait and see what the cleaning did. I am having a hard time talking myself into buying a $40 fuel pressure guage only to find out i need a $100+ fuel pump.

 

[modelageek]

on my truck i need to take the maf out of the hosuing to clean it ) i had to by some special torx for it . I agree with the post above the oil from the k and n mess up the maf. some thoughts , clean idle air control valve, fuel filter, fuel injector cleaner, 02 sensor

 

[Bajabronco]

Can of seafoam in the tank.......nothing
new fuel filter.....nothing
removed MAF from housing and cleaned again...nothing
cleaned the second sensor in the intake....nothing
I don't think it is the o2 sensors as it is reading lean on both banks.


Got a fuel pressure gauge today, connected it, turned on the key and 10PSI!
tried again twice and got 20PSI both times.
pressure while running is a steady 65PSI though i never had it under load.


So, it this fuel pump for certain or could it be the pressure regulator?

 

[Bajabronco]

Bump, anything guys?

 

[modelageek]

I don't know much about what the fuel preasure should be but I think the regulater is in the tank. You said you tested for vacuum leaks around the intake? How about your PCV valve. I know you said you clean the maf but I wonder if that could be bad.

 

[Bajabronco]

I just did a few more tests:

I hooked up the pressure gauge again, by cycling the key i could get it to build full pressure (65PSI)

Second, I pulled the vacuum line off of the regulator, no fuel leaked out and with the engine running it didn't seem to make a difference in the fuel pressure if it was connected or not.

After reconnecting it with the engine off, I could turn the key on once and pressure would then jump to 65PSI then start to fall rather rapidly, maybe 5 psi a second.

Every time after this (I tried 5 times or so) i could get it to read 65psi after turning on the key once....


I think this means the pump is fine, possibly just a bad regulator?

 

[modelageek]

Where is the regulater is it on the drivers side fender I know there is a fuel damper on the fuel rail. One more thought on the maf that could make you fail the emisions test. If your regulater is right there in the engine bay that would be cheap and easy compared to the pump

 

[Bajabronco]

maybe i was looking at the dampener, small silver module bolted to the passenger side fuel rail with a fuel line going into it and a vacuum line going into it?

 

[modelageek]

I was thinking this was the 4 cyl forum. I am not sure where your regulator or damper is. One other thought bad injectors can cause that issue but I would think the truck would run lousy?

 

[modelageek]

my damper looks like that and is on the fuel rail. I don't feel like rereading the posts. Does the truck run lousy?

 

[Bajabronco]

No, truck runs great.

 

[modelageek]

So I quess that means it seems to run ok. Then after you hear from some peeps about the fuel presure and that is fine and you checked your pcv. I am going with a bad maf.