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Thread: engine stutter

  1. #1
    FEP Power Member fgross2006's Avatar
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    Default engine stutter

    I have an 84 LX 5.0 with CFI.

    Overall the car runs great, Perfect idle. no codes when I scan, drives great.

    What I have noticed this summer is when i hit a bump the engine stutters, if I hit a patch of bumpy road the engine will stutter and the car bucks until I am driving on flat road again. Also I noticed that when i close the hood with the engine running the idle drops to almost stall then recovers.

    When I was troubleshooting an air conditioning issue last month I noticed I could sometimes make the engine stutter when touching the wire loom. So obviously I have a bad wire that effects the idle and is sensitive enough to complain when i hit bumps.

    I assume the only way to find the source is to pull off wire loom and separate wires and wiggle until I find the wire causing this issue. Has anybody else had an issue like this? Does it seem more likely the wiring to the fuel injectors or ignition?

    The stutter is the same symptom I got when my O2 wasn't grounded correct and earlier this summer when my ECT went bad. Neither of those are an issue now. No codes, car runs like a Swiss watch until I hot a bump, or close the hood.

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    Sounds like a bad ground honestly

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    FEP Power Member fgross2006's Avatar
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    Quote Originally Posted by erratic50 View Post
    Sounds like a bad ground honestly
    sounds logical except that i just swapped the engine 2 summers ago and I meticulously cleaned every contact on the engine and in the engine compartment.

    It seems to stumble when I touch the wiring and also the connections going to the solenoid cluster on the driver side inner fender.

  4. #4

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    How is the insulation condition at the ignition module? Is it still a Duraspark? Those sat next to the exhaust manifold and basically cooked the insulation. Mine was rock hard and chipping off when I located the source of my stall on right hand turns. It's easy enough to check. Then put some electrical tape between the wires and test drive.
    W

    As always, "It ain't what you don't know that gets you, it's what you think you know that just ain't so."

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    FEP Power Member fgross2006's Avatar
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    Quote Originally Posted by WilliamCapri View Post
    How is the insulation condition at the ignition module? Is it still a Duraspark? Those sat next to the exhaust manifold and basically cooked the insulation. Mine was rock hard and chipping off when I located the source of my stall on right hand turns. It's easy enough to check. Then put some electrical tape between the wires and test drive.
    I dont have a duraspark. I have a TFI and its relocated behind the front grille in a heat sink.

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    FEP Super Member gr79's Avatar
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    Had similar with my EFI Ranger.
    Sudden stutter, even stall going over bumps. Flashing ck engine light. Finally no start. No codes.
    Dealer rewired something in the under hood fuse box but did not cure anything.

    Was fuel pump relay working loose 1/2 way out of its socket. Fuse box cover stopped it from coming out of socket.
    Kept coming loose. Pushed it back down in socket, good to go.
    Foam tape solved that. Filled gap above relay. Stopped relay from moving up to the fuse box cover.

    Then had ICM cause bucking, stall, shaking, tach bounce, no tach. Worse and worse. Failed the other day, prob heat.
    Weird part once warmed up, drove fine. Surely something else is amiss.
    The ICM wiring down there has a glitch too. Found a rubbed out bare spot in the wire insulation.
    Intermittent ground out of CKP. Temp fix with foil and tape. Still is not right. Can fault it moving harness.
    Does throw OBD I codes though not specific to the CKP or anything else but the ICM and coil packs.
    Installing good spare MC ICM today and test close to home. Have added extra ground leads from ICM screws to fender.
    It will function temporally un monunted and grounded, but gets hot of course without heat sink (bitch loc on intake manifold).
    Have read there is a TSB on the ICM wire connections. Not followed up yet. Dealer part costs and labor rates scare me.
    Last edited by gr79; 08-13-2019 at 02:13 PM.

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    FEP Power Member fgross2006's Avatar
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    Yesterday I changed a duraspark connector that sits in the passenger side corner near the AC accumulator/drier. The female connector had dry rot on one of the wires. I had to buy a duraspark ignition module and cut off the female 4 prong connector to get a donor part.

    Anyway, after I finished that and srted the car I was able to find and induce the stumble condition by wiggling this 3 wire connector just under the front of the air cleaner. I think it goes to the fuel injectors. Not sure because it was getting late and I didnt feel like pulling the air cleaner to play some more. I remember when i first got my car this connector was a problem and my mechanic fixed the wires with new prongs and a rubber plug that sits inside this thing. Apparently after 4 years its acting up again. I'm sure this connector is not a replaceable part. Any thoughts on just cutting it out and replacing with a generic 3 wire connector?

    Also, notice I can make the car stumble for the first 20 seconds of this video but after that I cant induce it anymore. Thats what I get on the road. It stumbles sometimes but runs like a charm other times.


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    FEP Power Member fgross2006's Avatar
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    I am gonna cut this out and replace with a 3 wire trailer hitch connector. They are water tight outside connectors.

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    FEP Power Member fgross2006's Avatar
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    I was about to swap the stock TPS connector for a generic trainer hitch connector but had second thoughts on that. Theres no doubt now that the connector is the issue. As I stated earlier my mechanic (or rather his younger brother) "repaired" the male connector when i got the car around 5 years ago. He cut and sliced in new wires, crimped on 3 new male prongs and replaced the rubber plug at the bottom the 3 wires go through.

    with the air cleaner off I played a bit and realized if I push/pull the black and orange wires I create the stumble. the red wire is secure and messing with it does not cause the stumble. As a last resort I can splice in a trailer connector and Im sure it would be snug but I hate to do that because the female side of this connection is a part of the TPS switch and I would have to cut off the connector every time I replace the TPS.

    Im sure it wont be easy but I need to find the correct male connector in reasonably good condition.

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    FEP Power Member qikgts's Avatar
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    I think the end on this looks like its the same as what you need. Maybe cut the end off and solder it into your harness?

    https://www.ebay.com/itm/For-84-1986...kAAOSw7VRbMvbt
    '85 GT

  11. #11
    FEP Power Member fgross2006's Avatar
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    Quote Originally Posted by qikgts View Post
    I think the end on this looks like its the same as what you need. Maybe cut the end off and solder it into your harness?

    https://www.ebay.com/itm/For-84-1986...kAAOSw7VRbMvbt
    same shape but slightly smaller. Its got 2 wires. mine has 3 but capacity for 4.

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    Last edited by fgross2006; 08-19-2019 at 07:38 AM.

  12. #12
    FEP Power Member qikgts's Avatar
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    Second pic clearly shows 3 wires.

    Name:  o2 plug.JPG
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    Hope you figure something out.
    '85 GT

  13. #13
    FEP Power Member fgross2006's Avatar
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    Quote Originally Posted by qikgts View Post
    Second pic clearly shows 3 wires.

    Name:  o2 plug.JPG
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    Hope you figure something out.
    Those 3 wires are laid out in a triangle shape. Look at my pic of the female connector, Its a 4 prong, square shape with 1 wire left oit of the connector. That 3 wire connector is the correct shape on the outside but the pin pattern will not match mine.


    But I can see if my local parts store has one of those and see if it will mate up. If so I can buy a cheap O2 and cut off the connector
    Last edited by fgross2006; 08-19-2019 at 05:13 PM.

  14. #14
    FEP Power Member qikgts's Avatar
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    They sure look like the same layout to me. Maybe the picture below will help. I oriented your pic and another of the o2 connector so it should be more clear.

    Name:  side by side plugs.jpg
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    '85 GT

  15. #15
    FEP Power Member fgross2006's Avatar
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    Quote Originally Posted by qikgts View Post
    They sure look like the same layout to me. Maybe the picture below will help. I oriented your pic and another of the o2 connector so it should be more clear.

    Name:  side by side plugs.jpg
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    Yeah I agree. I have been looking over pics of various O2 sensors all day and it appears to be the mating connector I need.

    I been looking at cheap O2's on ebay. They go as low as 12 - 15 for a no name brand O2. Do you think the pigtail will be good enough quality if the O2 is junky? I'm gonna ask my local parts shop whats the cheapest O2 they can get me. if they can get me one for $25 or less I'll take it. If not I'll take a cheap one from ebay.

    Also, Im not thrilled to be butt connecting the new connector in place but I am the worlds worst solderer. I just cant make 2 wires stay together. Do you think if I use the red butt connectors with shrink tubing it will give a good conduit for voltage? The TPS seems to be very sensitive to a bad connection.

  16. #16
    FEP Power Member qikgts's Avatar
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    There is certainly the chance that the connector on a el cheapo sensor could be of poor quality and have terminals that are the same but frankly, today, you could have the same hypothetically junky stuff on a higher priced one too. Maybe run down to the local boneyard? That's what I would do personally.

    As far as soldering goes, here is a good video that shows an easy and effective method. https://www.youtube.com/watch?v=rZoTzYhLHkw Don't be afraid to learn how to solder it's a skill you'll use forever once you get comfortable with it and practicing costs next to nothing. Just don't waste heat shrink while learning, that can get pricey.

    In my opinion, there is no issue with using butt connectors so long as you lay down a good solid crimp. To do that you need a quality crimping tool like this: https://www.alliedelec.com/product/t...112m/70039936/

    If you don't have one like that or a quality ratchet style crimper, you will never make consistent long lasting connections. I have a few of those T&B crimpers that I used every day for 10+ years and they are worth every penny.

    Good butt connectors are a must also. Like these with the heat shrink. They are fantastic for under hood stuff. https://www.alliedelec.com/product/n...c22c/70722157/ You can get away with using a good butt connector and applying a sealing style heat shrink. That would be fine too.

    EDIT: Added the below...

    I've never used these but they look idiot proof and have good reviews... https://www.amazon.com/Connectors-El...55413318&psc=1
    Last edited by qikgts; 08-19-2019 at 11:42 PM.
    '85 GT

  17. #17

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    Quote Originally Posted by qikgts View Post
    As far as soldering goes, here is a good video that shows an easy and effective method. https://www.youtube.com/watch?v=rZoTzYhLHkw
    I would add that using flux paste is a must. I know a lot of solder already has a flux core, but it never seemed to help. Using the paste made all the difference, particularly if you are having to solder in place in an awkward position.
    1985 GT owned since new

  18. #18
    FEP Power Member fgross2006's Avatar
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    I fixed it today. the O2 for an 86 has the correct connector I needed. Bought a Bosch on ebay for 20 bucks and sacrificed the sensor for the connector.

    I followed the youtube vid and found it most helpful. I soldered all 3 wires and got a perfect connection in a few seconds each. Now that engine stutter is gone. I shook the connector like mad, slammed the hood with engine running etc. No more stutter.

    Now I notice a metallic clanging under the car coming from the exhaust system. I think possibly a heat shield on one of the cats. well its always something.

    Thanks for suggestion to use an O2 for a donor.
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    Last edited by fgross2006; 08-24-2019 at 07:09 PM.

  19. #19
    FEP Power Member qikgts's Avatar
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    Quote Originally Posted by fgross2006 View Post
    I fixed it today.
    Glad to hear the repair worked and kudos for learning to solder!

    '85 GT

  20. #20
    FEP Power Member fgross2006's Avatar
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    Quote Originally Posted by qikgts View Post
    Glad to hear the repair worked and kudos for learning to solder!

    Thanks man. I appreciate it.

    I think my 84 is running better now that at any point since I got it. I accidentaly posted the wrong pic and tried to delete and they stayed in my post "ghosted" .

    The first pic is the old connector with the orange seal protruding out the bottom of the connector. The next 2 pics are the ones I meant to post. The O2 with pigtail cut off and the actual connector on the car with fresh wire loom.

    I'm gonna disassemble to old connector and see if I can re-pin it and keep it as a spare.

  21. #21

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    I'm glad you soldered it! 9 out of 10 times, if you have a problem and there's a crimped connector nearby, it is the problem.
    1985 GT, Sunroof, 5 Lug, Rear Discs, 01 Graphite Bullets, 88 forged piston shortblock, 2.02/1.60 Alum heads, Weiand Stealth, Holley C950 TBI, BBK Long tubes

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