SOLVED Engine stuttering and hiccupping before and after new parts. (transmission cancelling lockup)

lumbee1

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UPDATE: The engine stuttering/hiccupping was actually the transmission cancelling lockup. The fix was to adjust the brake sensor switch.


Driving home from a camping trip in September, I noticed my engine started to stutter and hiccup at approximately 70mph after driving for 10 to 15 miles. I was concerned but it seemed to be fine at lower speeds. The engine was rebuilt and reinstalled in Dec 2021 and only has 5K on the build. After doing some recent work on the engine, I found some crispy broken wires on the main engine harness so I purchased a new one and installed it. I haven't driven it on the highway after the work with the new harness since Sept but after 15+ miles at 70 to 80mph, the engine started stuttering and hiccuping again, just like before.

The stutter is an almost imperceptible jolt and the first few times it happened I thought there was an unseen bump in the road. When this happens, the engine ever so slightly drops power and picks right back up again. I'm not sure if this is a fueling issue (fuel pump or injector) or a spark issue (igniter). I have a slight oil leak (yeah I know) and the tach seems to bounce randomly sometimes. New brake booster, no CEL, and ABS/LSPV have been removed.

Parts replaced or installed so far to address the problem:
  • New colder plugs
  • New vacuum lines
  • Dielectric grease on plug boots
  • New distributor o-ring.
  • New radiator
  • New engine harness
  • Adjusted TPS
  • Adjusted accelerator cable
  • Adjusted throttle cable
  • Added trans fluid
  • New coolant and distilled water
  • TRD Supercharger

As stated, the stuttering was happening before all of this was installed.
I have a spare igniter that I'm going to install tomorrow but I'm out of ideas.
 
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Also check your flexible air pipe from the Air Cleaner to the Throttle Body. If the rubber has a crack in it, when the engine shifts under load or a bump, it will crack open a huge vacuum leak which can feel like a power drop out. Duct tape will fix it in the short term, and a new air pipe will cure it if thats the problem. Good luck,
 

lumbee1

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when did you last do a fuel filter service?
The fuel filter was replaced with the engine rebuild. It's only got 5K miles on it.
I've read these filters last for a damn long time. My original filter was 26 years old with 275K miles.
 

lumbee1

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Also check your flexible air pipe from the Air Cleaner to the Throttle Body. If the rubber has a crack in it, when the engine shifts under load or a bump, it will crack open a huge vacuum leak which can feel like a power drop out. Duct tape will fix it in the short term, and a new air pipe will cure it if thats the problem. Good luck,
Last item in the parts installed list fixed the rubber air pipe. Besides the problem existed with and without the rubber air tube.
 
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I would do a fuel pressure check and do a volume test, I have seen pressures in spec. but not enough volume to feed the engine.
 
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The bouncy tach - id be looking near the coil for loose wires and also checking the connections that hold each plug wire to the dissy & coil
While youre at it be sure to check the resistance on all your leads & if you have an oil leak that is getting on the leads or where they meet the spark plugs clean it all off and make sure its clean & dry

check your injector plugs as well, one or more may not be 'clicked' in properly
 

lumbee1

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The bouncy tach - id be looking near the coil for loose wires and also checking the connections that hold each plug wire to the dissy & coil
While youre at it be sure to check the resistance on all your leads & if you have an oil leak that is getting on the leads or where they meet the spark plugs clean it all off and make sure its clean & dry

check your injector plugs as well, one or more may not be 'clicked' in properly
This is a fresh engine rebuild. This issue occurred after the engine rebuild with old plugs and after the new harness, new plugs, and supercharger install. No oil on the top end at all.

My coil pack wire to the dizzy isn't in the best shape and I've ordered a new one. Igniter coil will be replaced today.

This issue only occurs after driving for about 15 miles at 70mph. I haven't seen it occur at lower speeds.
 
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You might swap out the TPS. I replaced mine the first time because of a subtle surging at high RPM, high load situations (mountain roads). I replaced the NTK replacement with a used Toyota TPS when I began to have a weird stumble/cutout at idle, which sounds a bit like what you're describing.

I think if you search for the part number on the TPS itself, you'll find a bunch of used ones in eBay. It's probably one of those parts that is worth having a spare around, regardless.
 

lumbee1

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You might swap out the TPS. I replaced mine the first time because of a subtle surging at high RPM, high load situations (mountain roads). I replaced the NTK replacement with a used Toyota TPS when I began to have a weird stumble/cutout at idle, which sounds a bit like what you're describing.

I think if you search for the part number on the TPS itself, you'll find a bunch of used ones in eBay. It's probably one of those parts that is worth having a spare around, regardless.
Original TPS died a few years back. Replaced it with a rockauto unit, it died after one year, installed a new OEM TPS.
 

lumbee1

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Have you replaced the pre-filter on the fuel pump?
No I haven't. I did consider the pump and pre-filter, however we leave for a 7 hour drive at 1pm today.
 

Comet

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Sock takes under an hour to change if you have one.
 

lumbee1

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There's been a new development. What I perceived as stuttering was not fuel or spark but rather the transmission hunting and dropping out of overdrive.

My 7 hour trip to Windrock was uneventful. The "stuttering" happened a bit at the beginning of the trip but was very brief. We cruised around the Windrock trails all day Friday and Saturday with no issues that I could tell. Sunday on the drive home, the first 2 or 3 hours was fine but then the transmission started hunting for gears. At 70 mph, it would cruise at 2400 rpm but then jump to 2600 rpm with no user input. It got even more weird when expansion joints in the road caused the transmission to jump from 2400 to 2600 or vice versa.

Towards the end of the drive it was stuck at 2600 rpm at 70mph and no amount of bumps in the road was making it change. Oddly enough fuel economy increased during this time but that could have been due to other factors.

As I was pulling into our neighborhood, I thought I remembered a transmission shift solenoid that could cause the issue but I need to search for more information.

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At 70 mph, it would cruise at 2400 rpm but then jump to 2600 rpm with no user input.

Is it dropping out of overdrive, or out of lockup? An ~8% change doesn't seem like enough to be a shift from overdrive. The A343F has a .753:1 overdrive ratio, and the A442F is .765:1. Both are 1:1 in 3rd gear.

I seem to recall someone having a problem with their 80 dropping out of overdrive due to a bad brake switch or return spring...
 

lumbee1

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Is it dropping out of overdrive, or out of lockup? An ~8% change doesn't seem like enough to be a shift from overdrive. The A343F has a .753:1 overdrive ratio, and the A442F is .765:1. Both are 1:1 in 3rd gear.

I seem to recall someone having a problem with their 80 dropping out of overdrive due to a bad brake switch or return spring...
Guess what. I have a brake switch that needs adjustment. A door close or bump would cause the brakes lights to turn on or off. When getting gear out of the truck, the brake lights would come on. I would jiggle the brake pedal to make the lights go off.
 

lumbee1

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Is it dropping out of overdrive, or out of lockup? An ~8% change doesn't seem like enough to be a shift from overdrive. The A343F has a .753:1 overdrive ratio, and the A442F is .765:1. Both are 1:1 in 3rd gear.

I seem to recall someone having a problem with their 80 dropping out of overdrive due to a bad brake switch or return spring...
So this was a bit confusing to me. Turning overdriver off with the button resulted in a massive spike in rpms as expected. This wasn't a huge spike but rather a noticeable jump in rpm, similar to climbing a slight incline on the highway. As more accelerator pedal is applied, the transmission will jump up about 2K rpm. It usually results in more noise but not a significant increase in power or acceleration. My Cruiser has done this for 10 years and I've always considered it normal.
 

roadstr6

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Mr. Jones,
You might want to inspect those three big harness plugs between the engine and transmission on the driver side. They live in a filthy location. They sometimes get corroded and cause random mayhem. Those connections are not easy to snap open / closed either, so they may not be totally engaging. They would have been opened up when the engine came out and put back together when the engine went back in. Not saying this is your silver bullet, but rather something to check.
 
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So this was a bit confusing to me. Turning overdriver off with the button resulted in a massive spike in rpms as expected. This wasn't a huge spike but rather a noticeable jump in rpm, similar to climbing a slight incline on the highway. As more accelerator pedal is applied, the transmission will jump up about 2K rpm. It usually results in more noise but not a significant increase in power or acceleration. My Cruiser has done this for 10 years and I've always considered it normal.

I don't think my US-market A442F will drop out of lockup from throttle alone unless it's enough to trigger a downshift. It *definitely* doesn't drift in and out of lockup just driving down the freeway.

Tapping the brake pedal -- like you might do to disengage cruise control -- will cause it to drop out of lockup.

Have you tried driving while lifting up on the brake pedal with your left foot? (Obviously not in significant traffic)
 

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