Code 41 and 91

Discussion in 'Fox 5.0 Mustang Tech' started by Haus, Sep 9, 2008.

  1. where can i find this gauge you speak of.
  2. You can get them at about any decent parts store. Here's an example of a newer version of one I have:

    Actron Fuel pressure tester

    Prices will vary a bit depending upon brand and if you can find one on sale.
  3. i decided to make one. but not one that stays under the hood.

    i got a gauge and a grease gun hose good up to 5,000 psi??. i got the coupler that connects the 1/8 npt male port on the hose to the 1/4 inch NPT male on the gauge.

    i know the schrader valve can come off of the fuel rail but if i got to use the Schrader valve to check the pressure i need and adapter to connect the other 1/8 npt port of the hose to the Schrader valve.

    once i get this part i'll see how it works. but i cant find one

    im sure it will work just fine since it looks just like FP gauge but cheaper cause i made it myself.
  4. ok i found the piece i needed to make my homemade fuel pressure gauge work. less the 20.00 BTW and i got a PSI of 41.

    my dad's buddy used his FP gauge that he bought, on it as well and it reads 41. so i made one thats accurate it seems.

    i checked the FP with the vacuum line disconected from the Fuel pressure reg. and plugged up the vacuum line.

    i think 41 is normal so on to something else.

    Vac lines are fine, FP is fine.
  5. Ideally you would be able to have someone monitor your fuel pressure while driving the car under load (when fuel demand is greatest).
  6. i cant imaging how you would do that? thats just me tho. haha
  7. Set the gauge under the windshield wiper and have someone watch it while you drive. Or hook up a cowl-mounted gauge for a passenger to watch.

    Don't try to watch the gauge yourself and be careful and all of that common-sense safety stuff.

    FWIW, I test O2 sensors the same way. Watching them at idle isnt too useful. Seeing if they peg lean at WOT is helpful. A passenger watches the DMM readings for me.
  8. Just read through and had a couple questions/suggestions:

    1 have you gone over every ground in the engine compartment and cleaned down to bare metal and re-installed? might sound dumb but mustangs are REALLY fussy about grounds, I usually install a massive extra one.

    2 have you put a vacumn guage on a manifold source? the testers are cheap and I saw where you said vacumn lines were fine but not how you came to that conclusion.

    3 do you have access to a known good MAF so you can swap and compare?

    4 My personnal mustang had hard to find electrical gremlins like yours and after much hair tearing I found my hego ground was broken several inches into the loom(your hego reading is borderline too good), the other issue was the actual under car O2 harness, it had been carelessly installed at some point and had several ugly places where it contacted exhaust, I pulled it and cleaned up the breaks and end of issues.

    good luck

  9. fuel pressure test?

    Hission50 jump in on this,,,im in a paper book ,and when i said code 41/91 went to H1,,if that is proper than ,im not sure if step H1 was done right..H1-install fuel pressure gauge,verify that manifold vacuum is connect to the fuel pressure regulator if applicable,start and run engine at idle,refer to fuel pressure specifications table,is fuel pressure within specs for the engine being tested?.....5.0 ma sefi...27-37...(key off 35-45)..if this is proper than H2-H3 are ability to hold pressure and fuel delivery?
  10. This is what I was trying to ascertain. He needs to test the pressure under a load, which is where a weak pump or restriction can show its head.

    Your 27-37 spec is with the vac line connected at idle (KOER). I would surmise the KOEO 35-45 would be for the vac line disconnected. The EEC is programmed to see ~42 PSI at WOT (no manifold vac to the FPR).

    My rule of thumb, and what is in some Factory manuals IIRC, is pressure should not be below 30 PSI at any time, and should be 39-45 at simulated WOT.
  11. Do you have an open breather installed as an oil cap on the RH valve cover? ... is the breather hose from the oil filler neck connected to the TB?...... if so, you need to restore it to the OEM configuration (oil cap and breather hose).

    You could also use the system to verify O2 signals, cause an obviously rich condition whil a KOER is run..... disconnect and plug PCV valve and FPR vacuum, or you may also want to add some fuel through the FPR vacuum line from a container (not allowing the engine to stall)..... and check if codes 42/92 show up instead. This will help in isolating the codes possible cause as non-EEC related. LUK
  12. ok for the life of me cant figure out how to connect it to the shcrader valve and have to by the windshield wipers without closing the hood on the hose. any tips about this.

    excuse my newbiness but when i disconnect the stuff you said and plug it up. i pull the line out of the FPR and plug that line?? and do i pull the whole PCV and plug the hole or just pull the hose out of the pcv and just plug up the the PCV
  13. procedures

    This is step H18,, i have asked already if fords manual is the true step by step to troubleshooting,,,it is,,,code 41/91 or 42/92 both start at H1...FWIW,,anytime a part is changed and problem is still thier ,you must follow all steps starting at step this manual fuel control has 30 steps ,not that all 30 are for 41/91. some like hission50/jricher might have short cuts learned over the years,but this is why troubleshooting is so hard,, one bad ground can cause all this ,or something not looked at so thats why pin test done in order works.
  14. Haus

    was reading the steps over again and as to hission50`s train of thought on where hes going ...I forgot to follow my own words,,,were thier any other codes present... at the first time you check it, to now if you were to scan it,all of them even if they dont show now.
  15. all i get is 41/91

    i cleared the codes. i made sure to trip a code. i started the car with the MAF sensor disconnected to get a code, turned off the car and then plugged in the maf. and checked it to make sure the code popped up. it did and also the 41/91.

    i cleared the codes

    Checked the codes again. the maf code went away but as usual the 41/91 code was there.
  16. if i can ask you a question too.

    are you nosman??
  17. PCV... remove hose from valve and plug hose, leave PCV valve open, also remove TB to oil filler neck hose and plug TB port.... leave oil filler neck hose open.

    FPR vacuum line..... remove and plug it, run a KOER and check if codes 41/91 show again. If they do......

    Take a container with some fuel, unplug FPR line, start KOER self test let the FPR vacuum line suck some fuel from the container (you have to make sure you don't let the engine stall during the KOER)... check if codes 41/91 show up and LUK.
  18. am i nosman

    NO ,and i have no idea of whom your speaking of,,,,i got hooked on stangnet awile back,,and all the other replyers are who im learning from,,, as to your code..fuel control section asked if other code were present which would have to be addressed first,,, and your problem is like class for me.