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'96 Toyota 3.4L won't accelerate

posted Jun 19, 2016 21:20:27 by P Peterson
FIrst post here. I discovered Paul’s channels some time ago and have learned quite a bit from the book and videos. I really appreciate all the effort Paul puts into his quality content.

‘96 Toyota Tacoma 3.4L 5 speed, 210K
I was hoping to get some advice on some trouble I’m having w/ my truck. If I try to accelerate at more than a conservative rate it will hesitate, shudder. If I back off on the gas or downshift, it will accelerate.

I”m looking for direction. I don’t what to just be a parts swapper here. Just because it was due anyway, I did put in a new set of plugs, fuel filter and cleaned the MAF.

I have all the basic tools. My only ‘scanner’ is the Torque app and a OBD2 bluetooth dongle.

My timing belt is due to be replaced (it probably has 120K on it). Gas mileage has always been in the 21-23 range and is unchanged. Aside from the acceleration issue, it runs fine. No CEL or codes.

At idle, LT fuel trim is +3%, ST bounces around +/-3%. Driving straight and level LT +2.5 ST +/-4. During an accel, LT +2-+6, ST +4/-3.

Any thought on direction and checks checks I can make? How could I check for plugged injectors or a timing belt issue? How would an EGR issue present itself?
[Last edited Jun 19, 2016 21:21:52]
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8 replies
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Tyler said Jun 19, 2016 22:44:50
Hey sir, welcome to the forums!

First off, thanks for providing some great basic info in your post, really helps us help you. My first thought about your hesitation/shudder under load symptom is an ignition issue. I saw that you changed the plugs already (which is cool), but still leave us with the coils and wires.

There's several different ways we could check for injector, EGR or timing belt issues, but I'm not sure any of those fit your symptoms. Injector issues usually result in bigger fuel trim issues, a jumped timing belt would be more consistent, and an EGR problem (sticking open, for example) would cause rough running at idle.

I feel like you would have said so, but any stored codes? Early OBDII vehicles are hit-or-miss about misfire detection, just hoping for a little help.

If you have an incandescent test light or spark tester, I'd suggest doing some spark stress tests on the coil secondary outputs. These Toyota waste spark coils are a bit unique, in that they have the coil-on-plug output for the right bank plugs, and a plug wire output for the left bank. You'll want to test the spark out of each output individually, looking for differences in distance/color/sound.

This ScannerDanner video demonstrates the spark test I'm thinking of. Sorry, I don't think Paul has done a similar test on your design of ignition coil, but the same idea applies.
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cheryl hartkorn said Jun 19, 2016 23:52:33
id try using an adjustable spark tester the one you adjust the gap and perform a stress test on the coils/wires. also mist the plug wires with water and check for voltage leakage. ive found many bad wires that way. hesitation under load and shudder seems like an ignition issue
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juergen scholl said Jun 20, 2016 01:56:02
Does the upstream O2 sensor go rich when you go WOT? This would eliminate fuel delivery issues. Indeed in your case the ignition system is more suspicious than the fuel delivery. Apart from stress testing the coils inspect the terminals/plug wires and measure their resitances.
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MattWhite said Jun 22, 2016 15:29:54
I'm with Tyler on blaming the ignition system. Diagnosing with limited tools I'd look for white deposits of where the spark has tracked or leaked from a lead or down the side of a coil boot. The 5vz motors we see have COP one side and leads across to the other. Figured yours is the same. The spark tester is also a good one.
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P Peterson said Jun 23, 2016 04:55:13
Thanks everyone for taking the time to reply and for the suggestions. I'll take a look on Saturday and report back.

Yes, it's a 5VZ, w/COP on the R side w/ plug wires going over to the L.

No codes.
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Tyler said Jun 24, 2016 01:31:53
Thanks everyone for taking the time to reply and for the suggestions. I'll take a look on Saturday and report back.

Yes, it's a 5VZ, w/COP on the R side w/ plug wires going over to the L.

No codes.


Cool, thanks for getting back to us!
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P Peterson said Jun 26, 2016 20:47:31
Well here's a bit of an update. I did test for spark (using a Lisle COP[ spark tester). All would jump a 1/2-5/8" gap. The sparks ranged from orange, purple to blue. I was testing it after driving 5 mi or so.

The plug wires were all 15-20 KOhms. I haven't tried the water method yet.

THis morning, it ran perfectly, Although I only drove to the point where it was just warmed up. It's certainly possible it's a heat sensitive deal
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Tyler said Jun 26, 2016 21:54:15
Well here's a bit of an update. I did test for spark (using a Lisle COP[ spark tester). All would jump a 1/2-5/8" gap. The sparks ranged from orange, purple to blue. I was testing it after driving 5 mi or so.

The plug wires were all 15-20 KOhms. I haven't tried the water method yet.


Sounds like pretty good results, overall. The orange ones are a bit concerning, possibly an indication of weak spark, which would match your symptoms. If you wanted, you could try cranking the gap out to failure (where it won't jump the gap any more) and see if there are big differences.

THis morning, it ran perfectly, Although I only drove to the point where it was just warmed up. It's certainly possible it's a heat sensitive deal


Ahhhh, now that's interesting. You did the testing yesterday, and drove it this morning, right? That would suggest that there may have been a carbon track on one of the plugs/wires/coils that got disturbed during testing, and hasn't yet had a chance to fail again.
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