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1993 T100 - Jerks under acceleration

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Old 04-05-2017, 06:13 PM   #1
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1993 T100 - Project and Question

Hi,

I have a 1993 Toyota T100 3.0 L that I have been fixing up. She was real ugly when I got her but I saw the potential. I will post some pictures in case anyone is interested and has questions about my project.

Anyways, when driving on long trips, after about an hour the truck will begin to jerk under acceleration (rpm over 4000). It feels like a misfire and the truck jerks repeatedly. The strange thing is if I turn the ignition off and immediately turn it back on, the truck will ran fine again for another half hour or so.

Does anyone have have any ideas what could be causing this and why turning the ignition off temporarily solves the problem?



Last edited by bbonde10; 04-05-2017 at 06:25 PM.
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Old 04-05-2017, 11:44 PM   #2
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"Trucks real ugly" and I see a near perfect truck? lol. Come up in Michigan some time, it's worth probably $3k over here in that shape it appears to be in. Here's my 98 T100 SR5 that's worth around $1500 to compare to. My cab corners are rotted out (large holes on underside), and rockers are not long for this world (I got a good angle that doesn't show the rust so well).

*Ignore the junk in the background, yards a work in progress lol*


Anyway, sounds like you have a miss under heavy load (maybe high rpm or vibration based). I'd start with plugs wires cap rotor as basic tuneup items unless they were changed not too long ago. If they were just changed or anything just before the problem started, that's a good starting point to check too. Personally I always buy OEM brands, like NGK and Denso.

Do you have a check engine light on? Pulling the codes either way might give us a hint to if it's a misfire in the same cylinder, or a random miss. Been a lot of injector and fuel rail problems on the 3.0L posted lately.

Good luck with the diag work.
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Old 04-06-2017, 08:58 AM   #3
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Thanks for the reply! It looks better in that picture but I had to replace both cab corners, spot in the rockers, and somebody had slapped bondo on the bed to make it look like it was free of rust so I put a new bed on.

No check engine light and I did replace spark plugs about 4 months ago. As far as wires and other ignition components, would shutting the ignition off solve the problem? I would think basic ignition issues would persist all the time and not just went the truck has been running at high rpm for an extended period of time. I did put a new fuel tank and fuel pump in the truck. I could have messed something up when doing this. I am 20 and this is my first project. There's a very good chance I made some mistakes along the way.

Last edited by bbonde10; 04-06-2017 at 09:06 AM.
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Old 04-06-2017, 09:32 AM   #4
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It's hard to say with some electrics/physics, when things act up, they don't always act the same. Never had turning key off then on fix ignition problems. I was mainly looking at the miss @ high rpm, and if you don't know when the general tune up parts have been last changed, it's not too crazy expensive to replace them so you know. Air filter and fuel filter isn't bad to add to the list too.

For the key off/on making a difference, about the only thing I can think of would be a weak/bad relay where when it gets hot it'd have a weak push on the internal contacts, and the vibration from the high rpm being enough to make/break the connection a little. EFI relay is hooked to the ECU and some other parts, so that's a pretty good target. Also the COR (circuit open relay, basically a fuel pump relay) would be my 2nd relay target. Just a poor connection anywhere in the ignition system/relays etc could do strange things too. Could leave the engine running and start wiggling the two relays, some wiring around them, and on the ignition parts (distributor, igniter, coil, ecu). Careful of the spark plug wires, they can give a good zap if they somehow see you as being a better ground than the spark plugs. While you're at it, with the engine off, unplug and plug all the spark plug wires on both ends too and on the coil. They should click on the spark plugs when all the way on.

Kind of a lot of directions at once, but if you find anything at all that effects the engine, it would be a good indication where the problem is sourced from. Testing the relays might be a little hard to do if my theory is right since they would test find with the normal way you'd test them.

Diag work is sometimes the hardest thing to do, changing parts is more or less the easy part. There's whole businesses around the idea of purely diag car/truck problems and never wrenching on them besides the bare min to get to connectors and such.
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Old 04-06-2017, 05:21 PM   #5
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Thanks for the advice! I will check my relay connections and make sure everything looks secure. I also think I'll go ahead and change my plugs and wires. If that doesn't solve it, I have a parts truck that I can rob some other ignition parts off to try such as coil and igniter.

Do you know where I can find a good engine diagram? I had a service manual but someone stole it along with a bunch of other things out of my car. Probably should just buy a new one.
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Old 04-06-2017, 08:07 PM   #6
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This isn't exactly the service manual, but it's the engine wire diagram, covers the whole truck's electrical for all variations. Kind of a pain that the files are separated by section but that's how it is on the toyota tech site.

If you can't extract it, you'll need 7zip or winrar installed. Didn't think of that till after I uploaded it.
Attached Files
File Type: rar T100 - 1993.rar (2.09 MB, 6 views)
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Old 04-06-2017, 10:08 PM   #7
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Awesome, that's what I was looking for. I just ordered stock plugs, plug wires, distributor cap, and rotor. For about $100, this seems like a good place to start as you mentioned earlier. These parts, minus the plugs, were likely about due to be replaced even if not directly related to the misfiring.

Last edited by bbonde10; 04-06-2017 at 10:11 PM.
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Old 04-18-2017, 07:45 AM   #8
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Thats the best truck to do a 3.4 swap in , i did my 3.4 swap into a 93 T-100
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Old 04-18-2017, 07:45 AM   #9
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super sexy, i own 3 T100's
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Old 04-18-2017, 07:46 AM   #10
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run a can of liquid b12 in that rig, should clean her up, fuel system wise
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Old 04-18-2017, 09:12 PM   #11
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Thanks for the advice! Unfortunately, I did a compression test and found out that my number 1 cylinder has no compression due to burnt exhaust valve . I will be swapping the head and will replace head gaskets, timing belt, and other gaskets in the process
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Old 04-21-2017, 12:06 AM   #12
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Thanks for reporting back your findings. Wasn't expecting burnt valves O.o, didn't think the 3.4L had that problem, the 3.0L I've heard does though so it kind of makes sense.
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Old 07-06-2017, 08:00 PM   #13
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Bad ground?
I had all kinds of mysterious problems going on until I improved the ground from battery to frame and block.
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Old 07-16-2017, 08:46 AM   #14
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Quote:
Originally Posted by kapnd View Post
Bad ground?
I had all kinds of mysterious problems going on until I improved the ground from battery to frame and block.
^^^^
Ditto for me (3.0). The grounding bolt for the ground wire for the ECU was iffy at best and caused all types of strange behavior. The bolt that holds the ECU ground wire to the body was rusted and snapped off when I tried to remove it. The ground is under the air box on the driver side fender well. I drilled and tapped the old bolt hole / nut, new bolt and some dielectric grease. Knock on wood, it seemed to clear up a lot of weird problems.

PS: If you don't mind me asking, where did you score a nice looking bed like you have?

Last edited by KidSheleen; 07-16-2017 at 08:48 AM.
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