91 troubles

[liqhx2]

ok these are my problems
truck starts fine no prob.
idles rough and inconsistant 500-1200
bad gas millege about 130 to a tank
i got code 63 throttle position circut fault, below minimum voltage and also code 66 MAF circut below voltage
is there any guids for checking for shorts? thanks Chris

 

[Alec]

First try cleaning the MAS (MAF) and see if that helps.

 

[liqhx2]

got any tips on howto get the torx off with out a security bit?

 

[Bashman]

Originally posted by liqhx2
got any tips on howto get the torx off with out a security bit?

A hammer and small punch will take the center post right off.

 

[liqhx2]

CLEANED

cleaned MAF and no change could there be a short? is there any way to really check the MAF or TPS?

 

[MrShorty]

Any time you have an electric circuit, you have the possibility of a short.
circuit is quite simple. The PCM supplies astabel reference voltage to the TPS. The TPS itself is a simple potentiometer (variable resistor). As the TPS rotates, the resistance changes, and, as a result, the voltage drop across the TPS changes. Testing the TPS circuit is pretty much as simple as verifying the reference voltage, and making sure that resistanc changes smoothly and consistently throughout it's range.
The MAF is a little more complicated. It requires battery voltage adn ground (kind of an excitation potential), then the signal and signal return wires for the computer to actually read the amount of air flowing into the engine.
I don't remember all the specifics off the top of my head, but, if you can get a hold of a proper repair manual with circuit "pinpoint" tests and such, it will walk you through the diagnosis step by step. Many times, they can be had at libraries (libraries here like to carry Mitchell or Motor) If you don't want to go that far, at least get a wiring diagram and check it that way.

 

[liqhx2]

could bad spark gap make it get these readings? and what is the proper gap? thanks Chris

 

[liqhx2]

this is what i have done to no alail
1. cleaned MAF
2.changed IAC with other IAC out of my parts X
3.changed throttle sensor
4.checked for vacum leaks
5.checked spark gap
6.changed out coil pack
is there supposed to be a whining sound from the fuel tank pump?
could the fuel filter need to be changed? why would it be using so much gas? this is driving me nuts i can't figure out what the heck is going on
also the CEL comes on when i'm doing about 30-35 1-2000 rpm and if i mash the gas it'll go off i need some serious help

 

[Alec]

wouldn't be the fuel filter with too much gas.

could be the fuel pressure regulator.

 

[AspenX]

Fuel pressure regulator

When I had this problem about 3 yrs ago codes were saying O2 sensors and all kind of things. Of course we replaced all the things the codes said with no changes at all. We replaced the f p r and that fixed it instantly.

 

[liqhx2]

how can i test the FPR? where is it located? thank everyone for helping me i sould be narrowing on the problem shortly this is such a pain in the ass

 

[MrShorty]

With the check engine light coming on, do you still get the same trouble codes you were getting before?
And testing the FPR is best done with a fuel pressure gauge attached to Schrader valve on the fuel rail. And don't forget to check the vacuum line to the FPR for gas (should not be any in that vacuum line).

 

[katt68]

where is the fpr ?

where is the fpr located and this vacume line ?

 

[liqhx2]

changed out the pcv valve and it idle good for a while but now its crapping out again i can't get it right

 

[Opera House]

That "below minimum voltage" can mean that there is no power being supplied to the sensor. This can be a bad connector at the computer or at the bulkhead connector on the engine. Suggest you measure voltage at sensor connector. Doesn't two sensors with the same problem sound suspicious? Codes can make life so easy if you just read beyond the first two words.

 

[liqhx2]

checked voltage and looked and looked for any bad wires now i reset the codes and i think i've taken care of the power problem (bad MAF) but now i'm getting code 41 (lean O2 sensor reading) and my truck is running FULL RICH very stinky. what are the causes of it running to lean? what to check for before i replace the O2s and how many O2 sensors does a 91 EX have? thanks for everyones replys

 

[MrShorty]

'91 only has one O2 sensor.
The fact that it is running rich even though the computer is getting a lean signal from the O2 sensor suggests that the lean reading is false. This can be caused by a leak in the exhaust upstream of the O2 letting excess oxygen into the exhaust stream, a broken wire on the O2 sensor, or a bad O2 sensor or other O2 sensor circuit fault.

 

[liqhx2]

so either a vacum leak or a bad o2? i've got a parts EX is it safe to take the o2 out of that one cause i know its good and put it in mine or are o2s picky? thanks Chris

 

[liqhx2]

also another thing where should my temp guage be hovering at? mine normally sits right below the N in normal then once in a while it'll go up about half way then back down is that normal? and what is the esiest way to look for vacum leaks i've tried spraying ether on the intake and hoses to listen for a change in idle and i haven't found anything thank a bunch Chris

.. would a cold engine make it think it's lean? i've never had this bad of a time tracking down a problem.....it's a pain in the @$$