Rough idle and check engine light

[RaveOn]

Hi Gang

I am new here and I have a question. I have a 1991 explorer with a 4.0L engine and the check engine light comes on and goes off intermittingly and this started 200km's ago. Now when I start it it idles rough (possibly not hitting on all cylinders) and there is what looks like condensation with black soot (possibly unburnt gas) out of the tail pipe. Once it warms up it runs normal. I was thinking a bad gas cap as first and I'm also thinking about the fuel pressure regulator. Any other idea's? The truck has 230k on it and it has always ran great. Any help would be appreciated. There is no smoke out the tailpipe at all when it is running.

Thanks

Kelly

 

[BrooklynBay]

Welcome to this forum! You first have to get the codes read to avoid any possible guess work. Your vehicle has many sensors that could be causing a check engine light to display. A rough idle could be the result of a MAF, IAC, O2 sensor, etc. AutoZone reads codes for free in the US. I don't know about Canada.

 

[Darrman]

If I had to guess, I would say its a bad 02 sensor, but yeah, get the codes before you start spending money, that check engine light is the computer trying to tell you something.

 

[proffessor1979]

I pretty much have the same problem. I replaced all my 02 sensors about 2 years ago or so when i got my exhaust put on.

I just called Autozone since reading this thread but this place only can check the computer on 96's and up. Is that for all autozones or do you think just for this particular one?

If so any ideas where to go? I don't feel like spending an arm and a leg just to get it checked then have to spend more money

I have to get my inspection next month so this check engine light needs to go away. I was thinking about changing the plugs/wires since its pretty simple just to see if that does anything and also the fuel pressure regulator as stated above. Is that difficult to change?

I called pep boys and it's 89.95 for engine diagnostics...why would one place do it for free and one charge 90 bucks..then you have to pay to fix it if you want? That's beat.

thanks.

 

[BrooklynBay]

You could buy a code reader, or a scanner instead of paying everytime you need to have a code read. Check this link: http://www.explorerforum.com/forums/showpost.php?p=1483871&postcount=3. This explains how to check the codes without a code reader.

 

[proffessor1979]

Thanks, maybe I'll give that a shot. Have you tried it? Also does the computer store more then one code at a time or would i have to get it checked one code at a time..ex code **, fix problem, another different code, fix that problem etc.

And the self testing connection is easy to find?

 

[BrooklynBay]

The self test connector is under the hood. The computer does store all of the codes at the same time, but it would be a good idea to clear the codes once you fix the problems. Look at WWW.FordFuelInjection.Com for more information about how car computers work.

 

[proffessor1979]

Thanks again. It says to clear the codes disconnect the jumper during the test. I thought i read that if the problem is fixed it should clear in a certain number of start-ups or something. Sorry for being stupid here.

 

[BrooklynBay]

It should clear on its own, except for codes which are stored in the continuous memory. There are a few different types of codes. In my thread on EEC-IV codes: http://www.explorerforum.com/forums/showthread.php?t=160035, it states the 3 conditions:
C—Continuous memory code.
O—Key On, engine Off self test code.
R—Engine running self test code.
I went to AutoZone today, and asked them if their scanner could read anything under 96, which would be your EEC-IV system, and they said no.

 

[BrooklynBay]

Here is another link to read up on the EEC-IV: http://www.veryuseful.com/mustang/tech/engine/eec-IV-Tech98.zip

 

[natedogco2007]

advance auto parts also does it for free in the states. i work at an advance and i do that like all day. we have the stuff to hook it up to an obd 1 or obd 2 computer. it's all free and most times you get pretty good advice too. when you see these codes day in and day out they tend to learn what normally causes em.

 

[proffessor1979]

Sweet, Advanced auto parts it is. You just saved me $90 beans and they can do my truck.

So since you do this everyday do you get pissed when people get the free test, take their results and just leave?

NOw I need to find a replacement seat.

thanks again for everyone's help. Sorry to hijack your thread also.

 

[proffessor1979]

So after about 40 minutes and the guy finally realized he put in info for a 95 instead of a 94 we finally got some results.

He only gave me readings for the KOER tests

I got the following

KOER Code 327
EGR Sensor
Below minimum voltage

KOER Code 538
Insuffisient RPM
Change
During Self-Test

KOER Code 536
Brake On - Off
No state change
during self test.

Would any of these make the Check engine light come on? I'm guessing the EGR one, but what does EGR feedback signal is low mean? How do I fix that?

 

[BrooklynBay]

I know this link is for OBD-II, not EEC-IV, but it will tell you about the EGR sensor (DPFE): http://www.explorerforum.com/forums/showthread.php?t=164517

 

[MrShorty]

When diagnosing the EEC-IV system, SOP is to start by working on any KOEO codes. Since he didn't give you any results from the KOEO test, I would suggest that you start by getting someone to get you the results from the KOEO test. If you want to try doing it yourself, you might review my "notes on pulling EEC-IV codes" in the EEC-IV forum.

A couple of notes on those KOER codes: KOER 538 and 536 are almost always operator error during the KOER test. Your parts counter guy neglected to press the brake and goose the throttle at the appropriate times during the test (suggesting to me that, other knowing how to hook up the test equipment, he doesn't know any more than you do about diagnosing these things).

Finally, I expect the problem will end up being in your EGR system, but we need to get an accurate picture of what the computer is seeing so we know where to start our diagnosis.

 

[proffessor1979]

Is the DFPE the same on all years? I thought i remembered reading it was different on 94 and under.

So basically I would have to get the tests done all over again? WOuld it be worth paying the 90 bucks to have it tested? I mean I'm thinking they are going to use the same kind of tester.

In theory if i wanted to replace the system entirely what parts would i need and would it be that difficult? My main concern at this point is passing inspection next month and getting the check engine light to turn off.

In about 6 months I'd like to trade in my 94 and get a newer X

I just checked the napa online store and put in all my trucks info, and they have EGR valves and some other things, but they have different item#'s and some are different prices. What's the difference? Would any of them be fine?

They have EGR valve, EGR control solenoid and the EGR valve mounting gasket which i think will need regardless.

but there is a $20 price difference in the EGR valves themselves
one says w/ OEM # E6ZZ-9C915-A
the other w/ OEM # E6AE-9D475-B2A

Also I can't find the PFE sensor

 

[andybl]

Classic case of the fuel pressure regulator -- running rich with intermittent check engine light. Also - oil will smell of fuel and thin out. Fuel use will increase.

 

[proffessor1979]

Classic case of the fuel pressure regulator -- running rich with intermittent check engine light. Also - oil will smell of fuel and thin out. Fuel use will increase.

That was my initial thought, but it didn't say anything about that during the test. Also, the check engine light stays on after about 2 to 10 minutes of driving. Doesn't go off.

 

[andybl]

Mine started intermittent then ended up on all the time. Also, I don't remember the exact code when I dumped it out but it was something like "oxygen sensor reads rich". It turn out this is a common failure. The Diaphragm in the regulator fails allowing fuel into the vacume line. This in turn causes the engine to run way to rich. Excess fuel also washes down the cylinder wall and gets into the oil. This happpened at about 200K miles.

Andy 1992 sport 213K miles

 

[proffessor1979]

Both the EGR valve and the fuel pressure regulator do look like they are corroded pretty badly.

Would an EGR system problem most likely be from the PFE or the valve itself, in a standard case? I'm just trying to figure out what i can buy this weekend.

I'm going to look for the fuel pressure regulator now online

on a side note my truck has just under 135K at this point...