No-load stumble on 1FZ-FE at highway speed (1 Viewer)

[bryson]

Preface - 1996 FZJ80 138,xxx miles - I completed a head gasket job recently (<200 miles ago,) so I'm guessing the issue lies with something I disturbed during that project. Full valve job, head studs, OEM gasket set, new plugs/wires/cap/rotor (all OEM.)

When on the highway under little or no load, it has a pretty bad stumble/hesitation (flat ground or slight downhill with cruise control on is when it is the most noticeable.) No CEL, no jumping needle on the tach (or RPM fluctuation on the SGII.) Happens in 3rd or OD, CDL locked or open... Seems to only do it at higher speeds, and only once the engine is warm (closed loop only?) The truck runs good otherwise, idles smooth @ ~650 rpm, timing set to 5-6* BTDC, runs good while under power or decelerating on the highway, power is as expected. Intake hose was replaced with a stainless piece with silicone couplers, so I don't suspect that it is leaking. Sometimes I'm pretty sure I can hear slight backfiring when it is stumbling, which makes me think it is engine related (not VC or torque converter?) O2 sensors are original as far as I know.

I removed and plugged both vacuum hoses from the "T" on top of the EGR valve itself, and the stumble was still there, so I don't think that is the problem (I guess a vacuum leak elsewhere in the EGR system could still be an issue?)

As part of the HG project, I installed a VC120 vapor canister to replace my bunk OEM one, so I wondered if that could be part of it. I plugged the purge line between the canister and the purge solenoid, but the stumble was still there.

I parked next to a good friend with a 94 to compare vacuum routing, and it all matched (except for his extra PAIR system components/plumbing) as far as I could tell without tearing intakes off.

I'm guess it could be wiring after disturbing the harness, but If anyone can think of a place to start based on the symptoms that would be a huge help.


Thoughts?

Thanks in advance.

 

[bryson]

Where's the Saturday morning mechanics?

 

[oilbrnr]

Dude! I've got the same exact problem after getting mine back together last Saturday! Same list of parts as well. All vac hoses were either nice and soft, or replaced. I also had the injectors serviced. Since I was tired of working on it and needing it fixed, I took it into Camelback Toyota on Wednesday. Tech rode with me, but due to traffic we were never really able to reproduce it, but later in the day spoke with Murf and the thought was the #6 injector. That was put in yesterday, and at the end of the day, I guess it runs worse.

They are going to work on it again today and I'll update this thread with any findings. Service adviser said the tech did find some crispy wires which I'm sure refers to the EGR area, but I was gentle with and I perceived things to be fine. I had applied dielectric grease to all connectors not sure what kind of prep and or cleaning you did on your harness.

It is frustrating as like you said there is no code, and apparently there is little other computer type diagnosis available on these things. Good to know that you've done all the other investigation into vac/EGR bypass.

The way it acts, it has to be something electric related as it is such a short and sudden shudder.

 

[oilbrnr]

The fact that both of ours are experiencing the problem once warmed up, and like you said in closed loop mode, seem to be a key to figuring this problem out. I just don't have enough understanding of the systems to know where to start.

 

[blkprj80]

I'm not sure if it matters closed or open loop, but my OBDII system in my 1996 would tell me which cylinder was misfiring when I had a couple bad injectors.

Check your grounds. If you did a HG recently, there is a ground wire from the firewall to the head on the RH side. There are also some grounds on the LH side around the coil, and one that attaches at the engine lift bracket on the left front of the head.

 

[oilbrnr]

Thanks, but I know the grounds are back where they should be, and I had no active or pending codes on the ScanGauge. Not sure if it gets all the codes but I'm pretty sure it does.

Time to start looking for that 6.2 LS...

 

[bryson]

Grounds good here too. I kept all the factory ones, and added a few HD ones from fourrunner.

Still stumped.

 

[oilbrnr]

Just picked her up from CBT. I'll post after the drive home. Getting lunch now. Could have been a couple of things including intake manifold leak. I do see some foil insulation tape around the EGR area.

 

[bryson]

So, I drove some laps on the freeway today, and in between laps I systematically plugged/capped each vacuum line that comes off of the throttle body or manifold. AFAIK, there are the 4 right on top of the throttle body, and one on the front side of the upper intake plenum (that has a temp? valve threaded into the manifold.)

plugging each of the 5 lines separately made no difference in the stumble/hesitation.

Did I rule out a vacuum leak or VSV issue? Is there a vacuum source that I missed? Any other thoughts or suggestions?

Since it only stumbles at highway speed, closed-loop (I think?) can someone tell me a sensor or circuit to check that is only active during these conditions?

This is not fun.

 

[blkprj80]

Stumbling at highway speeds might be fuel delivery.
But you say it flutters at light throttle, so that doesn't make sense really. Fuel would drop out under load.

How are your plug wires?

Your drop out, is it random, rhythmic, or something else?

Did you set your timing after the HG job? With the jumper in the diag connector?

 

[bryson]

Timing set to 5-6* btdc with jumper in place.

Drop out is consistent as long as I'm at very little/no load, but it isn't rhythmic.

Plug wires are new OEM as are the plugs, cap and rotor.

Fuel injectors were cleaned while out, new fuel filter installed. I agree with you though, I think a fuel issue would manifest more under load.

 

[blkprj80]

What happens if you turn off the O/D switch?

How about the same RPM/load, but in 2nd, like 25mph maybe?

Wondering if it might be your locking torque converter... That would suck bad.

 

[oilbrnr]

Well, after picking mine up today, nothing is different. Still not what I'd consider a real smooth idle (but I'm going to have to experience a few really well running 80's to judge against I guess) and still a vibe at speed.

I'm beginning to suspect a tire or driveline issue that is now magnified by the new rear Slee double swing bumper and roof rack. i.e. I added those items during the same time I was working on the head. I also have 15 gallons of gas on one of those rear swings and a ARB fridge in the back. (I'm testing how she is going to handle fully loaded as I prep for a Canyonlands trip in May). Thing is, it is not seemingly present under load, or when off the fuel. Just normal cruise starting about 50-55.

The General Red Letters are HEAVY at 90 some pounds a piece, but I had them road forced balanced and had zero issues prior to the HG failure. I work for Discount Tire (Corp HQ) so I'll take her in on Monday and have the guys spin the tires up and see what they find. It is time for the first rotation anyway and I'll have the spare introduced into the mix. Better to have those young boys deadlift that spare back up onto the swing than me!

Bryson I'm going to PM you with my phone #. Call me tomorrow when your free and lets discuss as I'm curious how close we are to experiencing the same problem.

 

[bryson]

When I turn the OD off, as long as there is still no load, the bucking persists. I'll double check, but I don't think the issue manifests as the lower speeds (like 2nd gear.) Also, I don't see the typical RPM drop that I'd expect if it was the TC locking and unlocking. The stumble/bucking isn't rhythmic, but it is quicker frequency than the TC can lock/unlock (I think.) I hope it isn't tranny related.

I am certain however that it isn't a drivetrain or wheel/tire vibration.

@oilbrnr, blkprj80 or anyone else interested, give me a call or text whenever. 8 oh 1 - 9 for 9 - 53 too 6

Thanks!

 

[bryson]

Double checked all grounds, re checked timing, tested and adjusted TPS, re checked for vacuum leaks, tested fuel circuit resistor, tested IAC...

Still no better...

 

[blkprj80]

In your first post, you said it only did it warm. I wonder if there is some temperature sensor that might be bad.
There is a TVV (Thermal Vacuum Valve) in the side of the head up under the intake. Maybe you bumped that, or pulled a vacuum line off? It has two vacuum lines going to it.
There also may be a temperature sensor other than what goes to the gauge to tell the OBDII system when to change the mixture once it warms up. I don't know on that one.
Good Luck!

 

[bryson]

I think it only does it warm - the problem is that there isn't anywhere close enough to my house to hit highway speeds before the engine is warm...

I have verified that both vacuum lines are still connected to the TVV, but I can't confirm that it is operating properly (and I don't want to remove it to test it...)

I will look into the temp sensors further - I just wish Toyota didn't put them in the second most inconvenient place known to man.

Thanks everybody for the help.

 

[bmac1996acc]

Just run 80 through your neighborhood

 

[inkpot]

I'm beginning to suspect a tire or driveline issue that is now magnified by the new ..... .[/QUOTE]

Certainly a possibility. Try pulling each driveshaft out, one at a time, and drive with the CDL locked to see if you can isolate the problem to one shaft or the other. John

 

[bryson]

Fixed it.

I had the plug wires off while I was re-checking the gap on my new OEM spark plugs (they were all good ,) and while the wires were off I decided to pull the distributor cap off to check things out...

Inside the cap I found that the spring-loaded coil contact had somehow come out of it's socket, and the spring had been guillotined in half by the rotor. Oddly enough, there was enough of the tiny spring left inside the socket and pressing on the rotor contact that the Cruiser still ran! The other half of the spring had found a magnetic surface inside the distributor and hung out there, but the actual contact had been tossed around inside the cap.

The cap and rotor were new as of the head gasket job, and were factory Toyota parts. Looking at the wear pattern on the rotor (or at least part of it,) it looks to me like it was working correctly for at least some time before the contact came apart, so I don't think it was installer (me) error...? No clue how something like that happens.

Anyways, I took the cap and rotor (and my receipt from CDan) to my local dealer, and after the parts guy and several service guys looking at it they warrantied them, and I walked out with new parts. Anyways, I put the new parts on, and it runs MUCH better!