diagnostic help!!!

[bmxr152]

So im finally getting around to take care of the engine light that comes on and off all the time. Ive already changed the o2 sensor intake manifold gaskets, maf sensor, plugs, wires, and cleaned everything out i can. Basically it runs perfect, but i have to smog it this week. So i did the KOER test and got codes.. 12, 41, 71. I noticed that the engine temp is always at low but feels warm, and sometimes go up and then shoots back down. Any help would be nice!

 

[fangsnu]

to me sounds like maybe a thermostat. Just thinking though it may even be your engine temp sender unit. No sure with out really looking at it.

 

[bmxr152]

If the thermostat is messed up could it cause a CEL and cause it to run lean, or read a lean code? Also says idle out of range (to high) code 12. Thats the only thing i have not tried, its a pain. But guess i got to do it.

 

[MrShorty]

KOER 12 is often more symptomatic than diagnostic: basically it means that the engine didn't run smoothly enough during the KOER test (I once got those idle codes when my 2 year old "assistant" turned the steering wheel during the test. The unexpected load from the power steering pump was enough to trigger the code).

KOER 41 is an O2 sensor code. A "false" KOEr 41 is easy to get if you haven't properly preheated the O2 sensor immediately before the test. I might suggest taking the truck out for a drive, then running the test as soon as you get back, to eliminate this possibility.

Not sure what the 71 is--my code list doesn't indicate what the 71 means for a 4.0. maybe misread??

While I wouldn't expect a bad thermostat to trigger any of those codes, if I knew it was bad, I'd replace it.

 

[Tony H]

I can't offer anything but comfort. My '91 'X' has done this since I bought it 6 years ago. I ran through the whole gamit and it still comes and goes when it feels like it. It passes N.Y. emissions this way, It gets 20 MPG, I have over 336K miles on it I don't sweat it

 

[cogs]

yes, sticking thermostat... hey, when you remove the radiator cap, is it green or gunky? put some cleaner through the cooling system, and see if it doesn't stop the sticking.

 

[bmxr152]

Well changed the thermostat and definitely runs a lot warmer now. but today i was driving and the fuel cut off, and tried starting it 10 times, with no fuel pump prime. Then i turned the key like 6 times back and forth, and it started. Why did the fuel pump shut off for that time? Is my pump going out?

 

[bmxr152]

When i checked fuel pressure it was like this one, just once it built up after a while it stayed at 35psi
http://www.youtube.com/watch?v=-agmZ7IbQLw

 

[MrShorty]

Why did the fuel pump shut off for that time? Is my pump going out?

Maybe. Personally I'd start by inspecting the rest of the fuel pump circuit (relay, fuse, connections, inertia switch). A wiring diagram will help (even the one in Chiltons).

 

[bmxr152]

Its wierd, it could be dirty or something. Ill check it out

 

[Tony H]

It sounds very typical of a Fuel Pump Relay getting tired

 

[bmxr152]

It looked alright, but today i was out in the fields and came around a corner and it shut off. Tried to start it 20 times and every time it would start and die. I didnt hear the fuel pump prime either. can the fuel pump just go out and could the relay cause this?

 

[MrShorty]

can the fuel pump just go out and could the relay cause this?

yes and yes. I know diagnosis can be tedious, but you should take some time (with a voltmeter and a wiring diagram), and see if you can see where the fuel pump circuit is losing power.

 

[bmxr152]

Well today when i went out to start it, the pump primed and it started and ran. Could the fuel pump do that or most likely the relay? Im getting a relay today so well see.

 

[Tony H]

Generally speaking. Even if a Fuel pump was starting to go bad, it doesn't usually stop while you are driving. If you are driving and the car conks out and you don't hear the pump Pressurize. It is more likely the Relay then the pump.

 

[bmxr152]

Well i got the relay but i dont see where it would go in, all i see is one set of wires plugging into the box of relays. I was driving it again today, and then at WOT it died, wouldnt start.

 

[shaggymane]

Thank Tbars for this one.

http://www.explorerforum.com/forums/showthread.php?t=208097&highlight=change+fuel+pump+relay

 

[bmxr152]

Well it looks like the previous owner hacked up the wiring and used some kind of 5 prong relay with only 4 being used. I dont know where to start now. If i had some pics you think i could figure out what wires are going to what?

 

[MrShorty]

I'm not sure how he "hacked it up," but each of those relays is a 5 prong relay with only 4 prongs being used. At that age, some people have had trouble with the connectors going bad -- maybe he simply dismantled the connector????

A suitable wiring diagram should help you see what goes where. If your '91 is like my '92, the wiring diagram in Chiltons shows a red wire, a black/yellow wire, a blue/orange wire, and a green/yellow wire going to the fuel pump relay.

 

[bmxr152]

Heres some pics of what mine looks like?