Engine Please Help Me Diagnose Issues With My 5.0...

Discussion in 'Fox 5.0 Mustang Tech' started by 5.0 CJ-7, Feb 24, 2014.

  1. First disclaimer: Yes, this thread is for my Jeep CJ-7 with a Ford Mustang GT 5.0 engine under the hood.
    Second disclaimer: I'm a Chevy guy. :hide: This Ford stuff frequently has me pulling my hair out.

    Third disclaimer: This thread is likely going to get long. I have a lot of questions that I haven't been able to find answers to.

    OK. Let's get started... :D
  2. Go to it.. That's what we are here for.
  3. Problem #1

    To start with, I am unsure of the exact year of the engine. I was told that it was an earlier block ('85-ish) that had been upgraded with a later EFI system ('89-ish). Personally, I think the guy who I bought the Jeep from was on crack. I do know that his brother built it, but that is about the only thing he told me that I believe. If my research has been accurate, the EFI components appear to be from an '86 or '87 car as there is no mass air flow sensor. Also, I find it very difficult to believe that someone would go through the trouble of transplanting a Mustang GT engine into a Jeep only to come back a few years later and swap in an entire EFI system complete with the computer and wiring harnesses. I suspect that the entire engine (complete with EFI, computer, and all wiring harnesses) were pulled from a wrecked '86 or '87 Mustang GT, but how can I find out for sure?

    Problem #2 (hopefully not really a problem...)

    The catalytic converters and most of the emissions components are long gone. It was like that when I bought the Jeep back in 2010. I would have personally kept the stuff if I had done this conversion myself. Regardless, I'm not looking to reinstall any of the stuff at this time since I rarely drive the Jeep. Here are the codes that have always been present. They have never concerned me since I understand what they are and why they are there.

    KOEO: 81, 85, 82, 84, 10, 11
    KOER: 94, 44, 33

    Interestingly enough, the EGR valve is still mounted on the intake. It has no vacuum to it (accounting for one of the codes), but I've never known if I should keep the electrical connector plugged in or not. I'm not sure what effects either option has on the computer, so for now it has been plugged in.

    Problem #3

    This thing loves to kill its distributor. I estimate that in the past four years I have rebuilt the distributor six or seven times. Since the Jeep is not a daily driver, that represents a lot of work for very few miles of enjoyment. I will expand more on the specifics of this at a later time.

    Problem #4

    What's up with these engines and the whole surging idle thing? I'm not sure that I have ever been able to get this engine to idle properly. Recently I've gone to work on this problem again, and this time around I'm determined to make it perfect. So far I have done the following:

    base idle -- set to 600 RPMs
    timing -- set to 10 degrees
    IAB/IAC -- fairly new and very clean
    TPS -- fairly new, passed all voltage tests, adjusted to .97 at idle
    vacuum leaks -- all new hoses and/or plugs installed, new PCV grommet installed
    10 pin connectors -- clean with dielectric grease
    fuel filter -- brand new
    fuel pressure -- 40-41 psi (KOEO), 35 psi (idle), 42 psi (idle with regulator disconnected)
    EGR -- clean (but see notes under problem #2)
    grounds -- primary grounds checked and cleaned

    edit- spark plugs have only 1000 miles on them and the spark plug wires are brand new.

    Problem #5

    I have found that the engine seems to run well when it is cold. The idle is smooth, and I can stab the throttle with no hesitations or stumbles. I assume this is when the computer is in an "open loop". As the engine gets hot, the idle starts getting rougher with some surging, and any stabs at the throttle result in heavy hesitations and stumbles.

    There have never been any O2 sensor codes present, but as part of my process of elimination I disconnected the O2 sensor harness to see what would happen. Much to my surprise the engine idled perfectly with great throttle response when it was both cold and hot. Unfortunately I am not sure what this means. By disconnecting the O2 sensor harness, did I force the computer to remain in an "open loop" where it is ignoring all inputs (including the ECT sensor, for example), or was the computer only ignoring input from the O2 sensors (which would seem to indicate that they are the problem)? I need to know what effect unplugging the O2 sensor harness had on the computer.

    Problem #6

    Last night I had the engine idling for quite a while. Quite unexpectedly it died and then wouldn't restart for almost half an hour. My gut tells me this is another ignition control module on its way out. (See problem #3.)

    Problem #7

    On rare occasions I get code 67 (neutral pressure switch or clutch switch circuit failure) when doing a KOEO test. This of course prevents me from doing a KOER test as well. The code usually goes away fairly quickly, but I read some discussions on how code 67 can cause a surging idle. The transmission in the Jeep is a manual with "granny low" from an older Ford F-150 or F-250. There don't appear to be any wires coming out of it, so I'm not sure what occasionally causes code 67 or how to troubleshoot it.
    #3 5.0 CJ-7, Feb 24, 2014
    Last edited by a moderator: Feb 24, 2014
  4. More to come...
  5. Thank you. I certainly appreciate any help you and the others here can provide. :)
  6. I realize that I posted a ton of information this morning, guys. Please don't let that overwhelm you or discourage you from replying in this thread. I assure you that I'm mechanically inclined when it comes to working on vehicles and very logical in the way I think. If you have questions or need more information before giving an answer just ask. Feel free to respond to any or all of the problems I listed if you have something to contribute.

    If it is generally preferred to keep the discussion to one problem at a time, I'd personally like to start with problem #5. The fact that the engine runs worse when it is hot has me stumped. Also, before I go spend $90 on some new O2 sensors I need to know why the engine ran better when I disconnected the O2 sensor harness at the firewall.
  7. have you done the base idle reset and checked out the surging idle checklist?
  8. Yes. The surging idle checklist was a huge help. Take a look at my list of what's been done under problem #4. I actually did find some vacuum leaks, so fixing those was somewhat encouraging.

    By the way, I just noticed that we can't edit posts after 15 minutes. That will make this thread even more confusing ... LOL! I wanted to add under problem #4 that the spark plugs have only 1000 miles on them and the spark plug wires are brand new.
  9. #4 edited
  10. Here's a couple of things to look at.

    problem #2 (EGR)- with the EGR is still present- OK for the electrical is plugged in. I would leave the EGR plumbing, if the EGR is still present.

    problem #4- Base idle should be set for 850 rpm. Adjustable by the TPS voltage.
    TPS- should be between 0.90 -0.99 - 0.98 is the sweet spot. I'm set for 0.99.
    Fuel pressure- should be 39lbs - 40lbs. Vacuum off.
    Spark plug- assuming you have the correct type- gap .35 for starters.

    A dynotune should be done. A tune should fix some things and will also reveal any potential weirdness as well.
  11. Thank you.
  12. Thank you for replying.

    Problem #2: In that case I will keep the EGR electrical connector plugged in. There is nothing remaining for the vacuum to be plumbed to, so that will have to remain inoperable.

    Problem #4: Can you please point me to where there is documentation showing that base idle should be set at 850 RPMs? Everything I found indicated to set it at 600 RPMs with the IAB/IAC disconnected (some sources also said to pull the SPOUT, which I did do). I would personally love a higher idle (it makes rock crawling with a manual transmission much easier), but I kept getting code 12 whenever I had it set much higher. Also, am I right in thinking that my fuel pressure is OK even if it is slightly higher than what you are indicating it should be?
  13. I speak from experience when I mention 850 rpm. I am running a different cam. 600 rpm is too low and my engine will struggle at such a low rpm, especially in the morning when its cold. So what you did for the idle surge is essentially correct.

    After following the Idle Surge Checklist, did you reset the computer? ie- disconnecting that battery. wait about 20 minutes. then reconnect and drive. The computer will then relearn its idle strategy.

    Stock fuel pressure is 39 lbs vaccum off. When you reconnect the vacuum, the fuel pressure should drop a little bit. Your fuel pressure appears to be OK. For troubleshooting purposes and personal voodoo, I would adjust it accordingly.

    You might also want to inspect and clean the Idle Bypass Valve. The cylindrical thing that hangs off of the throttle body. Spray the inside with carburetor cleaner, let dry and reinstall with new gasket. Idle will be a rough at first as the computer relearns but will eventually smooth out.

    It is possible to set the RPM at 850 rpm via the Idle Screw on the throttle body but it will throw off the TPS voltage and you will have to go through again the entire Idle Surge procedure. It may open up another can of worms so don't do it unless you feel adventureous. It sounds like your Jeep is a recreational vehicle- ?

    On the '86 and earlier 5.0 engines... They came out of the factory with a Speed Density setup. Do a search for the explanation. There is a conversion kit from Speed Density to Mass Air which requires a change of the EFI system, computer included. This was what the previous guy most likely did. The change from Speed Density to Mass Air was done mainly to reduce smog and stuff like that.

    Good luck.

    Edit: it's been a while since I read the Idle Surge procedure check. All that I mentioned above is in it. Follow the procedure and you should be fine.
    #13 Treachery, Feb 25, 2014
    Last edited: Feb 25, 2014
  14. See the surging idle checklist below for a starting place...

    You guys with idle/stall problems could save a lot of time chasing your tails if you would go through the Surging Idle Checklist. Over 50 different people contributed information to it. The first two posts have all the fixes, and steps through the how to find and fix your idle problems without spending a lot of time and money. I continue to update it as more people post fixes or ask questions. You can post questions to that sticky and have your name and idle problem recognized. The guys with original problems and fixes get their posts added to the main fix. :D

    It's free, I don't get anything for the use of it except knowing I helped a fellow Mustang enthusiast with his car. At last check, it had more than 134,000 hits, which indicates it does help fix idle problems quickly and inexpensively.
  15. Yes, the computer has been reset numerous times.

    I hope the fuel pressure is OK. I have no way to adjust it.

    Please see what I have already done under problem #4. The IAB/IAC is relatively new and very clean. I even removed it again to confirm this.

    Aside from the missing emissions equipment, the engine is all stock. I'd like to get the engine running correctly with the factory settings before I venture into making any tweaks on it. It didn't seem to like it the last time I had played around with a higher idle setting.

    Yes, my Jeep is strictly a recreational vehicle.

    I don't understand what you getting at here. My engine is a speed density setup. There is no mass air flow sensor on it.
  16. Done, done, and done! Your surging idle checklist is how I first found this forum back in 2010, and I have been frequently referring to it ever since. The things I have already tested and fixed (listed under problem #4) are a direct result of the information contained in the surging idle checklist.

    There are a few more parts I need to test, but I'm stuck on the O2 sensors right now. Why did the engine run better with them unplugged?
  17. The code 33 is telling the computer to turn the EGR fuction off. So even with the EGR valve present, it's not functioning. The code 84 may be related. You could be missing the proper vacuum connection or someof the wiring. Hard to see with no pic. But with the code 33 stored, the function is disabled so the engine isn't pulling fuel at part throttle.

    TPS sensor voltages are usually too heavily scrutinized. These are non-adjustable. ANy voltage from 0.5V to 1.1V is acceptable. The EEC will take this voltage upon startup and apply a value to it to indicate WOT. The reason the car seems to run better when you adjust the TPS (while running) is because the car has already taken it's baseline and you manipulating the TPS fools it into thinking the throttle is opening and closing, adjusting fuel and timing. If you do not have a TPS code...there is nothing to adjust on the TPS. Once the voltage goes outside the 0.5-1.1V range, you will get a code. Setting the TPS to 0.99999V is a waste of time.

    The idle is computer controlled. Base idle is what you want to set. Simply unplug the IAC and adjust the idle stop screw to the lowest idle you can comfortable run. Then, reset the computer, plug the IAC in and let it relearn idle.

    Running poorly with the O2 sensors is a sign that there is an issue with some sensor somewhere. Without knowing what's in the car, it's hard to guess. First thing I'd do is find the EEC and run the model to determine if this is a speed density computer, and if it's for an automatic, or manual car. Considering you don't have any MAF codes, i'd bet the engine is set up as an 86-88 Speed density car. Wh
  18. Now to nitpick...

    Problem 1

    Can you post a photo of the engine? While i realize parts can be swapped, the intake plaque should be a good starting point.

    1986 plate

    1987+ plate

    The main difference between 1986 and 1987+ are the heads, intake, EGR and throttle body. Tracking down ford part numbers on these parts would be your main start.
  19. Code 10 is a separator code. Basically what you got was this

    KOEO: 81, 85, 82, 84,
    CM: 11
    KOER: 94, 44, 33

    In the grand scheme of codes, this isn't bad.

    81 and 82 refer to the thermactor air circuit that pumps O2 from the air pump to the cats
    85 refers to missing charcoal canister
    94 and 44 refer to the air pump system being removed

    Code 33 and 84 refer to the EGR valve. WIth these codes present, the feature is disabled by the EEC. This might be worth repairing down the road.
  20. These are prob related. What ignition module are you using? most aftermarket ones are junk. Are you applying them with generous amounts of heat sink grease? Heat kills these things.