CHTS - problem or symptom or bad JWT ECU?

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  • #1

    CHTS - problem or symptom or bad JWT ECU?

    Been battling a running rough, low/sporadic idle, stumbling, running rich, lack of power, sometimes running perfect issue. '88 ECU with JWT 450 tune, MB "420cc" injectors, Cobra MAF, Walbro 255 pump. No vacuum leaks. Stock FPR with 174K miles. No EGR valve. No O2 sensor. Perfect compression. Good fuel pressure. Been through 3 IACVs. Squeaky clean MAF. Recently, and sometimes, it'll drive fine until 3.5k+ RPMs were it suddenly starts missing/sputtering under load and boost (idiotic but more boost clears it up). But that's relatively new and sometimes it doesn't do it.

    I replaced the CHTS with a factory Nissan sensor a few weeks back and it didn't change much. Sub harness has zero resistance and neither does the wiring harness to the ECU. It fires right up in the morning first crank of the starter. As it warms up it starts running like crap - sometimes worse than others. Today it started running real rough and sounded pretty bad. When I unplug the CHTS the idle jumps up and it smooths out. But it does it MOST OF THE TIME. Sometimes when I unplug it, while it's running like crap, the idle will jump up and the engine smooths out but when I plug it back in it'll stay the same for a bit then slowly start running worse. Most of the time when I plug it back in it instantly runs like crap again. Sometimes when coming to a stop the idle will be at 1K where I set it, smooth as silk and others it will be down to about 600 running real rough. When it comes to idle at 1K like it should, after 15 or so seconds it simply starts running rough and the idle drops. It's actually becoming a pretty severe problem. I made a video. I'm waiting for a new CHTS to come in so I can swap them out but it seems like there's an underlying issue and the CHTS is the symptom of something elsewhere not jiving with it. It doesn't even do the proper "rev-up" when you start it. Usually sputters to life but not as bad as in the video. I took the video today since it's running worse than usual.

    http://s273.photobucket.com/albums/jj20 … 737337.mp4

    Close to being at my wits end. Ideally I'd like to throw an entire new harness at it with a new ECU but JWTs are hard to come by and they aren't cheap. Don't have the money for Nistune so I'm kinda stuck.
  • #2
    Re: CHTS - problem or symptom?

    After I posted this I think my Cobra either failed or went way out of whack. It gave me a real good hiccup then started running super rich and consistently idling at about 500RPM. Driving it falls on it's face yet boost builds.

    Does anyone know off hand the values of the MAF at idle? I know it's a 2-7V system but that's about it.

    Scratch Cobra MAF. It's interchanged as '89-'93 5.0s, 3.8L Taurus, and a few Mercuries. Just the Cobra MAF housing.
  • #3
    Re: CHTS - problem or symptom?

    what about the air regulator on the pass side? did u change to a square style rebuildable one?

    what about the ecu. did you try without the shitty JWT ?
  • #4
    Re: CHTS - problem or symptom?

    I did, but I blocked it off and nope I haven't done that quite yet.
  • #5
    Re: CHTS - problem or symptom?

    Called up Jim Wolf, the MAF in my car isn't even the right one lol. Part number needs to be an F1SF not F1ZF from a '93 Cobra only. Sheitt. But it used to run fine with the smaller Taurus MAF so I'm going to yank one from a yard and see what happens.
  • #6
    Re: CHTS - problem or symptom?

    New MAF didn't change a thang.
  • #7
    Re: CHTS - problem or symptom?

    Did you find out what your voltage readings are?
    "Its the s12's sexy over weight step daughter, the z31"
  • #8
    Re: CHTS - problem or symptom?

    No he didn't give them to me. Said there's no accurate way of testing it on the car? I thought that was a little weird. When I read him the numbers off my MAF the first thing he said was "that is definitely not the right one for your ECU."

    But you rode in it, thing ran pretty damn good!

    Check this shit out, this is under half throttle:
    http://s273.photobucket.com/albums/jj20 … 513478.mp4


    It still runs a lot better with the CHTS unplugged. Chris got me a new one so we'll see but I don't think it's going to change anything. I was really hoping a new MAF would fix it, it sure dun did made a lot of sense… but fuck it, it was only $2. :nanan?re Bought a proper Cobra MAF and housing that'll be on it's way tomorrow for pretty cheap anyhow.
  • #9
    Re: CHTS - problem or symptom?

    Did the ECU input/output signal inspection. Power source and grounds for the ECU and to the sensors are good. Here's the problem areas.

    TPS (-) 0V when throttle is open or closed, should be 9-10V
    Fuel pump relay .75V, should be B+
    Fuel temp sensor 3.36V, should be 0.5ishV
    CHTS .78V plugged in and 4.93V unplugged, should be 1-5V depending on temperature
    TPS (+) 11.45V, should be 9-10V
    AFM .6V @ 5-700RPM and goes up to 3V when revving.

    Real time diagnostics show the fuel pump is bad however it primes fine and builds perfect pressure… I think the PO rewired it off the ECU though.

    FTS and CHTS are completely out of whack, especially the CHTS being plugged in VS. unplugged. What the fuck.
  • #10
    Re: CHTS - problem or symptom?

    I have the same issue so f*cking annoying!!!! If you figure out anything let me know please. I'll do the same. I've been trying to figure this out for 6 months now.
    Usual Z31 suspect: Garage Queen (aka broken)
  • #11
    Re: CHTS - problem or symptom?

    Will do man. I need to figure it out because it's my daily driver and it hardly drives anymore. When the green light clicks on the ECU it's REALLY bad.
  • #12
    Re: CHTS - problem or symptom?

    Another tidbit… when plugging the CHTS in to the hot idling car after it's been in the freezer for 5 minutes it runs just about perfect for a bit, then as the sensor warms up it craps out. I've ohmed this sensor next to another brand new one and it's spot on.
  • #13
    Re: CHTS - problem or symptom?

    Anyone got any ideas?
  • #14
    i can see in your video that your distributor is not as straight pointing (parallel with the intake plenum body) as it should be.

    my conclusion is that the distributor was rebuilt at some point with items from a pathfinder or maxima distributor.

    i'm taking a guess because that's the orientation my 16E00 distributor was and the car ran similarly to how yours is. it just wasn't controlling timing properly when the engine was warmed up.

    try changing the distributor and make sure the body of the unit says 21P00 or 21P01. if it's an old distributor, don't open it. try it with your cap and rotor first, and if it works out, remove the CAS and clean it up and put it back together. chances are it will work.


    thats my take. i dunno. just goin by how the diz is pointed in yer vid.
  • #15
    Thanks for pointing that out, didn't really occur to me because it times at 20* just fine lol. This thing did run like a raped fuckin ape till a few months ago when it slowly started going downhill and last week hiccupped real hard then got to the pretty much non drivable point that it is now.

    I just went and looked, says 22 100. May be a "P" but it's hard to tell.
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