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Misfire with AC on

Discussion in 'ZX2 1998-2004 2.0L DOHC' started by RonW, Oct 17, 2020.

  1. RonW

    RonW FEOA Member

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    Yeah that's what I thought. I was initially concerned about it, which led me to test the other car in same situation. It behaved similar
  2. Apex

    Apex FEOA Member

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    That would mean that both cars have an issue that is causing a lean condition. It's important to pay attention to what both the long term and short term fuel trims look like over different RPMs.

    As an example a vacuum leak will have a lean condition at idle, but will improve at higher RPM because the engine is not producing as much vacuum pulling in air from wherever the vacuum leak is. In this example your long term fuel trim may be at 20 at idle, but as you rev the engine up your short term fuel trim might go to -20, making the total fuel trim 0. If you were to hold it at a higher RPM your long term and short term might drop and increase, respectively, to 0. It is also possible since long term fuel trims is a learned response that LTFT may just drop to 0 at higher RPMs.

    Once the car is warmed up and running closed loop, what do the fuel trims look like at different RPMs? What does it look like when the car is starting to run hot?


    Edit: Sorry, I see now that you posted your fuel trims, I missed it due to the double post. A lean condition at higher RPM could mean a fuel delivery issue. What does your fuel pressure look like under heavy acceleration?
    Last edited: Oct 22, 2020
  3. RonW

    RonW FEOA Member

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    My long term trim is usually low, as in under 1 and closer to zero. During downshift exits or just cruising foot off the pedal all trims go to zero until I give some gas.

    The main reason for comparison of the two is the other automatic runs well, none of these issues and good gas mileage overall.

    Prior to the burnt shorted wire everything was fine. As I think I mentioned originally? After fixing the short I replaced both O2 sensors, the ECU, and ccrm.

    As for the short. I took the hot shorted wire out of the connector, cut cleaned and soldered the wire then capped it with a dead end coated terminal connector and taped it up. I then just sprayed the two ends with MAF cleaner and used compressed air to blow it out and reconnected it. I'm feeling I need to address that connection better?
  4. Apex

    Apex FEOA Member

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    It sounds like your o2 sensor is working fine, but if you're really concerned about it you could check your o2 sensor voltage, sensor 1 should oscillate between 0-1v and sensor 2 should remain pretty steady since the cat is doing its job. You could spray a little brake clean or any other combustible into the intake and see the o2 sensor respond seeing a richer air fuel ratio.

    There's a few different things that can cause a lean condition under load/high RPM such as a dirty or otherwise underreporting MAF sensor, a weak fuel pump, bad fuel pressure regulator, etc. It may be a good idea to look at the PIDs for MAF voltage or grams per second measurement, fuel pressure, etc.

    Are you able to log some your data or post screenshots of graphs?
  5. RonW

    RonW FEOA Member

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    MAF sensor was also replaced, and swapped and ultimately replaced with the new one. I'm going to try to get setup to get some pics of what I see. Cannot hurt to have more eyes on this

    If I'm able to then I will post them later this afternoon. I'm also doing another flush today before leaving work.
  6. Apex

    Apex FEOA Member

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    New parts are an expensive way to diagnose problems. If we can figure out where you problem might lie you can do a pinpoint test or tests to determine if that part needs to be replaced or fixed without guessing based on data, just like we did with your low speed fan issue. Much cheaper and ultimately faster way of doing things barring getting "lucky" if you happen to replace a part that is bad.

    I look forward to seeing your data, however it may simply run lean at high RPM because of the misfire, raw unburned fuel will not get detected by an o2 sensor.
  7. RonW

    RonW FEOA Member

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    I totally get what you are saying, fortunately with some of the aforementioned parts they were new in the sense of one of my ZX2 was "parted" up prior to me buying it, turned out to be a broken timing idler. Good for me, not so much for them. So a lot of parts came from donor vehicles. With that said I also will buy a $8 part if it's suspect just because it's a 20 year old car and the fact that I'm not really great with a multimeter definitely comes into play as well.

    That donor car has long since passed, but it's load of new parts sit on a shelf :)
  8. Apex

    Apex FEOA Member

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    Multimeters are awesome tools, my recommendation is that it is definitely a good time investment to get better with it. Scanners are also an invaluable tool for diagnostics, we're very fortunate to have powerful free software like FORScan.

    I'm starting to lean in the direction (get it, lean?) that the lean condition is caused by the misfire and we should probably focus on what is causing the misfire. Were you able to find the individual misfire counters on any of your scan tools? I know this will probably have to wait until you get home. Also if there is a power balance test and an injector balance test I would try those through FORScan, I have a feeling those aren't available on a Ford this old though.
  9. RonW

    RonW FEOA Member

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    Yeah I haven't found anything individual wise in forScan? I do have screen shots of the trims and also the $06 info from another app. I can grab the snap on scanner next week to see what I can do with it.

    I've been concentrating so much on the ECT that I didn't realize my trims are worse than I thought... a lot more movement than I remember and definitely is a problem there. Up to 15+ during flat stable driving a few times. I may have to put this out of service until I find out more. I have a CR-V to drive daily, just mpg is not great compared to ZX2.

    Will come back with more information
  10. RonW

    RonW FEOA Member

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    So I've taken a bunch of screen shots of pid's and some of the $06 stuff and I'm trying to figure out how to upload the photos on my phone? Any idea? Or should I get to a PC?
  11. RonW

    RonW FEOA Member

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  12. RonW

    RonW FEOA Member

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    So I think I can upload photos now. Since it only allows one pic at a time I'm going to weed out the more important ones. I'm away until tomorrow so not much I can work on. I put a picture of the plug I mentioned, it looks worse than I thought and definitely need to clean that out.
    In the pic the short was lower left and the orange wire that sat next to it is going directly to the upstream O2, that is the wire that was getting 12v pumped into it and controls voltage of 0.00 - 1.27 volts max, having 12v pumped into it I decided to change it out back then.

    Update: Change out the O2 sensor, not the wire.
    Last edited: Oct 24, 2020
  13. RonW

    RonW FEOA Member

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    Screenshot_20201023-061318.jpg Screenshot_20201023-061330.jpg

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  14. RonW

    RonW FEOA Member

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    Screenshot_20201023-061522.jpg Screenshot_20201023-061541.jpg

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  15. RonW

    RonW FEOA Member

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    That's all the $06 data I have. Oddly from another app that shows this data it only shows 4 items and all have passed. I'll attach them here. Screenshot_20201023-072330_FordSys Pro.jpg Screenshot_20201023-072335_FordSys Pro.jpg
  16. Apex

    Apex FEOA Member

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    Can you run a mode 6 test through FORScan? It's much more readable than whatever you're using there. Still going to try to go through a decipher these, But there should be a misfire rate for each cylinder displayed as a percentage which will display in FORScan. I want to know if it is a specific cylinder that is misfiring or if it is the whole bank.

    Then, for live data use these PIDs:

    CLOSED_LOOP
    MAF
    IAT
    MISFIRE
    LONGFT1
    SHRTFT1

    Take a screenshot of the oscilloscope after you get it to misfire so I can see the data over time rather than a static output. Also, if you can find a PID for fuel pressure that would be awesome.
    Last edited: Oct 24, 2020
  17. RonW

    RonW FEOA Member

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    So I didn't get a lot of time this weekend but I did finish the rad flush and found a semi rotted vacuum line which I replaced. One question is on the back of the throttle body are two push on vacuum connections, I sprayed them with brake clean and the fuel trims did react to it, so I may have a smaller leak on them? Problem is I don't see anywhere to buy those items? I actually cannot find anywhere to purchase any vacuum lines, as some do not take well to straight cut hoses... I'm thinking some vacuum leaks is having affect on those trims and it's something I want to address. It doesn't fix the bigger issue of the overheating but today's ride home will tell me if the flush helped. I also cleaned out the connector that I've been concerned with and I did notice a change in the load percentage PID.
    Another new issue is I did include the fuel PID which basically just says closed loop, however on occasion it would change to open loop, or OL-Drive. And not only when I was pushing the car but sometimes just cruising.
    I'm including some more pics, unfortunately forScan doesn't have some of the items you had mentioned before so I'll try the snap-on scanner this week.

    One item to keep in mind is the battery was disconnected when I cleaned the connector, so it is still in learning mode at the moment, P1000.
  18. RonW

    RonW FEOA Member

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    Screenshot_20201026-054631_FORScan Lite.jpg Screenshot_20201026-055013_FORScan Lite.jpg

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  19. Apex

    Apex FEOA Member

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    Sorry, I guess I should have specified FORScan for the computer, are you able to hook up a laptop? What I really need is a graph of this data, I forgot to include RPM when I was listing PIDs, I won't be able to tell you much from this data without knowing what conditions they were happening under, and even if I had RPM it's hard to tell when I just have still images of gauges. I really need a graph of the data.

    Your car will go into closed loop as long as it is warmed up. It will enter open loop if you are under deceleration and the car cuts fuel or if you go WOT. It looks to be behaving normally.

    The vacuum leaks will only affect the car at times of high vacuum which is under deceleration and idle. Won't really affect anything during fuel cut.

    Does your car have a schrader valve on the fuel rail? You might just hook up a fuel gauge to that and see if it drops when you free rev it. It should not really ever drop fuel pressure and there should also be a specification that I would have to look up for what the base fuel pressure should be.
  20. RonW

    RonW FEOA Member

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    Sorry about that, I may be able to get my laptop hooked up and connected. One small problem is my laptop battery is not so good and usually dies in 30 mins. But I'll give it a try.

    No Schrader valve.

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