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Thread: Sudden rough idle & Hesitations after parked overnight!

  1. #61
    Administrator Ron's Avatar
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    Quote Originally Posted by Bitsyncmaster View Post
    The six plugs will all fire in sequence no matter where the plugs are.
    ???
    I'm not sure why you replied with this -- I was talking about the cylinders firing, not the plugs.
    I was trying to straighten out the "left"-"right" thing...

    Quote Originally Posted by Bitsyncmaster View Post
    Now with two wires swapped, those plugs may fire at any of the four cycles of the stroke. I can't believe the engine would run without backfire or a blown exhaust with two wire swapped. Each cylinder still draws air and fuel on each intake cycle.
    +1!

    ...that or a break a piston or two.

  2. #62
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    I have seen motors (not Deloreans) where the firing order was wrong and the motor did idle OK but under load it had a noticeable loss of power. Mileage was horrible too. Maybe you are incorrect, and the firing order was actually correct? In any case check and recheck it to make sure you have it right now.
    David Teitelbaum

  3. #63
    Senior Member Beachdrifter's Avatar
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    My VIN:    * 5945 * Oct, 31, 1981. FranKenDeLorean

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    It lives!!!

    IT'S ALIVE !!! FRANKENDELOREAN LIVES!!!

    First, I have to say thanks to everyone who chimed in. I've been a member of the board since I owned my car back in 2005, and appreciate everyone's contributions.
    I too have contributed over the years here and there, but life is busy and sometimes I don't do it often.

    But when I have problems I come here, and I always make it a point to let others know how I fixed my issues to bring everything to closure, so others can benefit from it as well. In the 17yrs, this one has been the most challenging and hardest to figure out.

    I will summarize what the issue was briefly for those that are new to the thread.
    Early April I drove my car for about 30 miles (ran perfectly fine BTW), and left it parked overnight outside (was a special occasion, and the car never is parked outside overnight; it is always garaged). Next morning, the car started up fine, but throttle and idle was horrible. Had severe hesitation and the engine shaked a lot on idle. Just like that over 1 night the car started running like crap. I ended up towing it back home because upon driving, I felt like the car was going to shut off and the entire range of throttle response was just not right.

    Over the next few weeks, I did diagnosis in 2 phases. I will describe the phases below which includes things I checked and reason behind it.

    PHASE 1:

    1. Electrical:
    a. checked and cleaned bulkhead connectors. (i learned how dirty these can be over time and THEY DO sometimes fail to provide contact due to corrosion for current to
    flow causing all sorts of problems)
    b. swapped lambda ECU, idle ECU, ignition ECU with known good units for testing.
    c. checked grounds on lambda, ran test on lambda to test 02 sensor responses.
    d. checked fuses
    e. unplugged and cleaned every connector in the engine compartment I could find.
    f. changed alternator with new DMCH unit (unrelated, but I needed to do this anyways)
    g. replaced 02 sensor
    h. checked voltages at battery and car running
    i. replaced spark plugs
    j. checked spark at plugs, and at cables (all seemed to be good)

    2. Mechanical:
    a. swapped CPR/WUR with known good unit for test
    b. Checked operation of idle motor
    c. Checked proper operation of cold start valve (to make sure it wasnt sticking open)
    d. checked operation of frequency valve
    e. check for any loose vacuum hoses that were accessible.
    f. drained fuel and refilled (thought maybe i had bad fuel?)
    g. played around with the fuel mixture and dwell which caused my cat to glow for a few mins. probably was not the best idea to do that. so i stopped.
    h. replaced the vacuum valve at the back of the fuel distributor since it appeared it had a leak.

    After a few weeks of completing phase 1, it seemed that nothing had an affect on the condition. It still ran the same after doing all those things above. Even started chugging so bad it popped and crackled in the exhaust like it was angry at me or something.
    I realized at that point that maybe I had to go deeper. I came to the realization that I needed to go into the VALLEY OF DEATH to slay my demon.


    After a prayer or two, I rolled up my sleeves and got to work on the next part of the journey....

    PHASE 2: -- VALLEY OF DEATH AND MORE...

    Once you realize you have to go there, it's the mentality of "let me do that while I'm there anyways... " so at this point it was go for it all or go home.

    a. Replaced cap and rotor (my 17 yr old one looked good enough to me, but did it anyways). inspected distributor inside for corrosion or obvious signs of problems
    b. Replaced all new DMCH plug wires -- OK maybe I confused myself with the firing order issue i mentioned earlier. But you guys were right, there is only one way to go
    and it is clearly marked. My car must have been fine even before i took them off, and I confused myself during the process.
    c. Painted the air intake to chevy orange . Heck why not, I had to have a little fun with this too.
    d. Cleaned/vacuumed the valley. Checked the engine block to make sure I wasn't rotting down there. Lots of nice little crevices to explore in the valley.
    e. inspected fuel injectors and valves. Realized I should start using Techron on this car regularly on a 40+ old engine. Too much bad fuel out there.
    f. inspected and replaced all vacuum lines (most of them anyways except the canister ones) with red silicone. Although I didnt see any cracked or obvious hoses that
    looked like problems, maybe there was a leak somewhere I couldn't notice?

    g. REPLACED THE GREEN THERMAL VACUUM SWITCH IN THE Y-PIPE -- Now, here is the ONLY thing I could attribute to anything that had to do with TEMPERATURE. Seeing I left the car outside and the drop in temperature maybe did something to this switch?? Don't know, but one thing I noticed when I inspected it was that I could rotate the green part with some moderate pressure while the unit was secured by the threads. That didn't seem right to me. Perhaps some seal in between the green casing and vacuum path was drawing a leak? When I installed the new one, it did NOT exhibit the ability to be rotated or moved. So obviously something was not normal with my old one.

    5-13-22-ENGINE-FINAL3.jpg

    Took a deep breath, and patched everything back up slowly and to torque specs. I realized at this point if nothing in Phase 2 fixed my issue, then off to DMCFL would be for me.

    After PHASE 2 was complete, my Engine looked like this:

    5-13-22-ENGINE-FINAL1.jpg

    5-13-22-ENGINE-FINAL2.jpg



    Then came time to start her up. Naturally so, it took a few cranks to get her going. I figured the air in the fuel lines and fuel distributor needed to be purged before all the cylinders could get going . After a few minutes of cranking it and seeing her sputtering get better and better, she came ALIVE back to her normal self!!

    THE HESITATION HAS GONE AWAY, THE THROTTLE RESPONSE IS BACK TO BEING IMMEDIATE UPON START UP AND ACROSS ALL LOADS IN WARM, THE IDLE IS A PURRR AT 750 WHERE IT SHOULD BE. THE ENGINE VIBRATION IS NORMAL AS IT SHOULD BE. NO POPPING , CRACKING, OR FUEL/RICH SMELLS COMING OUT THE EXHAUST, OR SMOKE.

    SHE IS NORMAL AS FAR AS I CAN TELL. I let her idle and throttled it, testing responses for about 20 mins. All with full load of lights, AC, radio, and everything was normal.
    Turned her off again, and started again, she ignited and idled perfectly.

    OK, so mission accomplished as far as I see. Although I havn't taken her back on the road, it seems to be working fine.
    I wish I was smart enough to be able to pinpoint the exact cause, but between that green thermal switch, replacing vacuum lines, and doing overall cap/rotor, did the trick.

    THE ONE "BUT" ......
    Now, the only thing I am noticing is that after even an extended period of warm up 15 + mins, the DWELL is STILL not moving (sticks to 20 on the 8 cyl scale). Couldnt get it to cycle. Everything on the car sounds good, like before, so maybe this is something I've had for awhile and never paid attention to it until now.
    Is it ok to keep the car at this setting or should I look into this deeper? I can replace the 02 sensor again and see if that changes things?

    Otherwise, the car seems to be running back to normal. THANKS!!!!
    Last edited by Beachdrifter; 05-13-2022 at 04:11 PM.
    ** A wave is like an empty canvas, waiting for a masterpiece -- unknown **
    ** VIN 5945 - FranKenDeLorean Oct 31, 1981 ** SpaceCoast, FL, USA ** DMCTalk Member/DMCOwner Since 2005

  4. #64
    Senior Member Bitsyncmaster's Avatar
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    Congratulations on getting her running good. The frozen dwell first thing to check, is the FV buzzing? You can just jumper at the RPM relay connector the the double yellow/red wires to the brown and that will power up the lambda system and you should get 45 deg. dwell. No need to have the key on. That would be a good test for your dwell meter also. It may be your 20 deg reading (I guess your on 8 cylinder scale) is really 22.5 deg.
    Dave M vin 03572
    http://dm-eng.weebly.com/

  5. #65
    Administrator Ron's Avatar
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    I'd suggest (re)checking the pulse ratios at D:04:15, 5 in the WSM.

    P.S. Congrats!

    Chevy orange.

  6. #66
    Senior Member Beachdrifter's Avatar
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    Quote Originally Posted by Bitsyncmaster View Post
    Congratulations on getting her running good. The frozen dwell first thing to check, is the FV buzzing? You can just jumper at the RPM relay connector the the double yellow/red wires to the brown and that will power up the lambda system and you should get 45 deg. dwell. No need to have the key on. That would be a good test for your dwell meter also. It may be your 20 deg reading (I guess your on 8 cylinder scale) is really 22.5 deg.
    Thank you Dave, Ron,

    So I jumpered the RPM relay, key off, and I don't hear the freq valve buzzing. Just the fuel pump running. Also no reading on the dwell. I disconnected and played with the freq valve connector, and nada.

    With the car on, i feel and hear a clicking / vibration / "buzz" from the frequency valve.

    So with just the RPM relay jumped, I'm supposed to hear the freq valve clicking/buzzing? If that's the case, then something is definitely wrong somewhere and I am running open loop all this time I probably never knew it.

    during phase 1 of my diagnosis I did the whole lambda test thing where you disconnect the 02 sensor, then ground the lambda to see the different readings on the dwell low to high reading (i dont remember the exact procedure), but anyways it showed my lambda ecu was working at least based on that test i assume.

    Is this not electrical then and maybe I need a new freq valve?
    Last edited by Beachdrifter; 05-13-2022 at 08:19 PM.
    ** A wave is like an empty canvas, waiting for a masterpiece -- unknown **
    ** VIN 5945 - FranKenDeLorean Oct 31, 1981 ** SpaceCoast, FL, USA ** DMCTalk Member/DMCOwner Since 2005

  7. #67
    Senior Member AugustneverEnds's Avatar
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    Congratulations, so happy to hear you won your battle!

    Maybe you just need to clean the frequency valve, a cotton swab should do just fine.

    Welcome back to the open road!!
    Nick A.

    1988 BMW 325is
    1982 DeLorean DMC-12
    1989 Jaguar XJ6

  8. #68
    Senior Member Bitsyncmaster's Avatar
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    Quote Originally Posted by Beachdrifter View Post
    Thank you Dave, Ron,

    So I jumpered the RPM relay, key off, and I don't hear the freq valve buzzing. Just the fuel pump running. Also no reading on the dwell. I disconnected and played with the freq valve connector, and nada.

    With the car on, i feel and hear a clicking / vibration / "buzz" from the frequency valve.

    So with just the RPM relay jumped, I'm supposed to hear the freq valve clicking/buzzing? If that's the case, then something is definitely wrong somewhere and I am running open loop all this time I probably never knew it.

    during phase 1 of my diagnosis I did the whole lambda test thing where you disconnect the 02 sensor, then ground the lambda to see the different readings on the dwell low to high reading (i dont remember the exact procedure), but anyways it showed my lambda ecu was working at least based on that test i assume.

    Is this not electrical then and maybe I need a new freq valve?
    I'm guessing you jumped the fuel pump at the RPM relay unless you have a three pin jumper and jumped both the fuel pump (white/purple), double yellow/red and the brown.

    You just need to jumper the double yellow/red to the brown to get the lambda buzzing, no key required. If that does not get it buzzing you now need to troubleshoot why.
    Dave M vin 03572
    http://dm-eng.weebly.com/

  9. #69
    Senior Member Beachdrifter's Avatar
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    Quote Originally Posted by Bitsyncmaster View Post
    I'm guessing you jumped the fuel pump at the RPM relay unless you have a three pin jumper and jumped both the fuel pump (white/purple), double yellow/red and the brown.

    You just need to jumper the double yellow/red to the brown to get the lambda buzzing, no key required. If that does not get it buzzing you now need to troubleshoot why.

    Dave thank you. Silly me, now I remember why I had kept a 3 prong jumper in the relay compartment.

    So yes, I jumpered all 3 and got the frequency valve buzzing strong, plus dwell reads steady 24.5 at the same time.

    So looks like we established that. I assume that means my lambda curcuit should be working ? I also figured I'd swap in a new 02 sensor just in case.

    Hmm , What else could be driving the fixed dwell while the car is on ?
    ** A wave is like an empty canvas, waiting for a masterpiece -- unknown **
    ** VIN 5945 - FranKenDeLorean Oct 31, 1981 ** SpaceCoast, FL, USA ** DMCTalk Member/DMCOwner Since 2005

  10. #70
    Senior Member Bitsyncmaster's Avatar
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    Quote Originally Posted by Beachdrifter View Post
    Dave thank you. Silly me, now I remember why I had kept a 3 prong jumper in the relay compartment.

    So yes, I jumpered all 3 and got the frequency valve buzzing strong, plus dwell reads steady 24.5 at the same time.

    So looks like we established that. I assume that means my lambda curcuit should be working ? I also figured I'd swap in a new 02 sensor just in case.

    Hmm , What else could be driving the fixed dwell while the car is on ?
    Yes your lambda is working. If it still holds steady on a hot engine then I guess your O2 is bad or disconnected.
    Dave M vin 03572
    http://dm-eng.weebly.com/

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