vibration/shudder on acceleration (1 Viewer)

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Wiring harness near firewall? Don't know why i keep thinking it's an electrical issue
 
I have a 96 that has done the same thing about three times recently. I thought it felt more like an engine knocking/cutting out hesitation, thought possibly wire related. It only started when it got cold and it wasn't warmed up well.....probably just coincidence on the weather though. I have been keeping it in the garage and warming it up well since and haven't had it re-occur. I saw this thread while looking for engine rebuild info because I was thinking of this exact problem..lol. My systems are the same and occur just as described.
 
Okay…thanks for all the comments so far…it is much appreciated!!

I’ve scoped out all the wiring I can get my hands on…can’t find anything. But I ran out of daylight. I’ll be back at it later today.

Drained/refilled my transmission last night (did not drop the pan will this weekend). This morning the shudder is still there. Before it would shudder when accelerating and run fine when at a constant speed.

Took it for a test drive and it seems to be more persistent. It still seems to shift just fine, no clunk into or out of gear. But now it shudders pretty consistently when driving and after about 10mins it started to shudder when stopped.

While stopped the engine seems to lope…in a slow “whomp whomp whomp”…like a really throaty diesel engine…with the RPM needle shaking.

Pulled into a parking lot, popped the hood, and listened to it in Park. Engine sounds like it is missing…it has the normal engine sound…”whir whir whir” then a “whomp”…”whir whir whir whomp” (sorry…best sound effects I can type)

I’m going to replace the spark plugs and wires tonight. What else should I go after?
 
Since it got worse,I would probably rule out a motor mount. Since it seems to affect engine performance, it would probably be an ignition/electronic type of problem. Seems to be like one of the cylinders are not firing. I would try a cheap diagnostic test of spraying a fine mist of water on the electrical components and see if it stalls(or sparks in the dark). 25k on ignition wires doesn't seem to be too old especially if they are OEM. Why replace them if they don't look bad and they could be expensive.
 
Okay…think my sound effects were a little off. I went out and started my truck again, to see if the idle ‘looping’ was still there… and it ran fine at the initial high idle, but when it got down to around 6-700 RPM it starts up again.

Again sorry for my sound effects, but it’s the best way I convey what is going on. It’s not rhythmic like I initially thought, truck will idle fine then dip in a “whir whir whir whaa…whir whaa whir …whaa whaa…whir” Then every once in a while it will run smooth for 5 secs then start with the “whaa’s”. Each time the RPMs dip at the “whaa’s” the whole engine will rock.
 
one other really cheap try/fix....

Take all the plugs out and squirt air down the motor to dry any moisture that "may" be in there. Also let the plugs sit out and dry. While you are pulling the #6 plug you can inspect the wiring harness.
 
wingnutter:
Can you give more data on what is actually happening? "Shudder" generally refers to the tranny slipping then grabbing hard in quick succession; like a bumpa bumpa bumpa; A roughness on acceleration like the engine is missing badly, then causing a generalized vibration, is a different animal. Is the vehicle vibrating, "sputtering"?? ie: what is the engine doing when it is idling; ie: in park, hood open, and your standing outside the vehicle looking at the engine and one hand on the fender to feel vibrations? Is the engine obviously running rough and vibrating/shaking and/or looking like it is going to stall, or does stall??
 
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gray-

when idling, the engine seems to hesitate on random intervals. the normal engine rhythm is interrupted randomly with a hesitation that torques the engine, causing the truck to make an obvious shudder.

on acceleration, it is as if i'm rolling over small speed bumps. quick succession of hard shudders...buhbuhbuhbuh...you can feel thru the whole truck. I let off the gas and it stops.

If I am holding a speed, it doesn't seem to shudder at all...or at least not noticeable and once the RPMs drop to around 6-700 the idle hesitation starts.
 
What you now describe is the engine not firing properly, worse under load. What have you done or checked in the last couple of days? Recent fill-up just before it happened (still on the same tank of gas??). Could be fuel system (or fuel) related or ignition, lot of possibilities. If you filled up the tank in the last few days just before this occured, one easy cheap test would be to dump a couple of bottles of Isopropyl alcohol (the more expensive gasline antifreeze). I would assume however, that if you got water in your tank, it would be gone by now, or not run at all. It may be worth a couple of bucks to give it a try. I would check all your ignition wires, distributor cap and rotor, and plugs. Your vehicle does not have the OBD II port, so you would have to read any codes the old fashioned way.
 
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What you now describe is the engine not firing properly, worse under load. What have you done or checked in the last couple of days? MIL on? Recent fill-up just before it happened (still on the same tank of gas??). Could be fuel system (or fuel) related or ignition,
so far:
checked all wiring
drained/refilled tranny
checked plugs/wires
same tank of gas. fill up at the same gas station i always go to.

on tap:
replace plugs/wires
replace cap/rotor
drop tranny pan
replace fuel filter

lot of possibilities.
you can say that again. :confused:
 
Yes, there are, difficult to go through them all. I would first focus on the fuel system and also the ignition system. The tranny can wait. Just attack it one thing at a time as you are. All the routine checks.

The key bit of information you mentioned is that it started all of a sudden; so that indicates a failure in the ignition system or the fuel system (kinda Duh statement there). If you are lucky, it's just a tank of bad gas (rare to go on for so long if just water). The only time I have experienced similar to what you have described is when I got a bad tank of gas. but that was overseas.

Some other suspects; clogged fuel filter (under the intake), clogged fuel pump filter "sock", possibly a malfunctioning fuel pressure regulator. Have you looked at the engine harness against the firewall, near the EGR valve? Is it laying on the EGR pipe or does it looked melted??
 
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Read through this thread to learn about pulling codes, there are plenty more threads on this also if you do some searching.

https://forum.ih8mud.com/showthread.php?t=143088&highlight=te1

From that thread

MoJ quote:
"When the CEL is on, open the grey plastic lid labeled "Diagnostic" attached to the pass side of the firewall. Turn the key to "ON" but don't start it and have an assistant, preferably a hot one, sit in the driver's seat and watch the CEL. On the inside of the Diagnostic lid you'll see a map showing which terminal is which. Bend a paperclip to connect holes TE1 and E1. The CEL will blink to show you which code. Code 71 would be seven blinks, a pause, and then 1 blink."
 
so far:
checked all wiring
drained/refilled tranny
checked plugs/wires
same tank of gas. fill up at the same gas station i always go to.

on tap:
replace plugs/wires
replace cap/rotor
drop tranny pan
replace fuel filter


you can say that again. :confused:

Any news?
 
Check that all of your plug wire seals are flush and laying flat a friend of mine had the same problem after an engine cleaning. After his recent tune up one of his plug wires were run under the top seal and water filled the plug well. A little air and reseting the plug wire to the plug and he was running well again.
 
wingnutter:
Can you give more data on what is actually happening? "Shudder" generally refers to the tranny slipping then grabbing hard in quick succession; like a bumpa bumpa bumpa; A roughness on acceleration like the engine is missing badly, then causing a generalized vibration, is a different animal.


all right, it sounds like this is exactly like what I am going through right now.
But it seems like the diagnosis is all over the place.
I am having the same issues that he described at the begining. I have a viberation/shudder upon acceleration, and when I try to maintain speed. when I coast, it is smooth as glass. if i rev the engine while coasting. just as smooth. It only viberates/shudders under acceleration, and the more the truck is under load, the more it viberates.
It also seems to lack power, and mileage went WAY down.


The problem in my case is NOT in the engine, it is in the driveline somewhere.

my mechanic said that my rear end is in good shape. (thanks :D). But he says that there is a ton of play in the shafts coming out of my transfer case. He suggests a new transfer case. But I was advised by cruiser jimmy on this board to do a search on the board for more answers.
he said
"Do a search for your symtoms, It's in this forum. You may not need to buy a transfer case.

Possible problems:
Driveshafts are not in phase: that's one of the viberation problems.
Slop in the driveline is a condition we call clunking. It's pretty bad for the 91~92 models.
A '93 and above transfer case will not work in your vehicle, not with an '89 or below.
My TC has some play into also, but it's not causing a problem.
Also, sounds like to need to do a tune up.
"

so any more ideas?

THanks
Kent
 
hey guys. i know this is an old thread, but i wrestled with these same issues a few months back. it had nothing to do with engine or trans. it was a wiring harness issue. when in drive the torque of the motor would twist it far enough to rest that egr exhaust line against the wiring harness and short out a few of the wires to the ecu. i hope you guys got it figured out but just in case...

mike
 
Mine was a bad spark plug wire, replaced with new set and problem solved!

I had 100k miles on the odometer and still had the original spark plug wires!
 
That's some good feedback, eurorom!

Thank you.

Going to pull #3 spark plug and get a read on my own mess.
 

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