Judder on acceleration at 2k rpm, where to start?

[Jeff Elliott]

Hi Folks -

Jumped in the rig last night, found a hammered battery. Jumped it off and away I went. < 1 mile out of my garage, I picked up a judder on acceleration at 1800 - 2200 rpms and an intermittent drop of ~200 rpms when holding a steady speed. Rig ran great when I put it away last. I've not experienced this before other than when my harness was fried at the EGR tube which caused a misfire that was injector related. Wound up repairing the harness, all new injectors and an ECU (fried the old one) which solved the problem. FWIW, alternator was charging at 13.5 so I don't think this is voltage related.

I'm not sure where to start - I don't think this is transmission or driveline related... It feels like engine; possibly timing or fuel delivery? Would certainly love your views on where to start the diagnostics - my first thought was to pull the plugs and see if there are remarkable differences / findings.

About the rig: '97, <100k original miles on all components, turbo'ed with wits end kit about 3-4k ago, part time kit. I don't think the turbo is the issue as I'm getting boost (though a bit less than normal) and the AFRs look in range.

Thx in advance for any places to start!

 

[mudgudgeon]

Did you drive it long enough for the battery to recover a full charge?

 

[Rusty Marlin]

Did the ECU throw any codes?

 

[Jeff Elliott]

Did you drive it long enough for the battery to recover a full charge?

Not fully - have put in on the charger. That said, I did monitor voltage via scan gauge and voltage was 13+ volts the whole short drive

Did the ECU throw any codes?

None

 

[mudgudgeon]

I'd be suspicious of the battery even with the alternator showing 13.5volts

 

[Jeff Elliott]

Well, what do you know... Charged battery fully and drove her this weekend. So far, no recurrence of the issue!

 

[Jeff Elliott]

Well, the issue is back with a vengeance... and there's no electrical issues this time. It idles like a 4BT and runs like a tractor that's lugging.

I started it up and it ran smoothly like a sewing machine. Then, after only about a min, it started running very rough... Here are a couple of videos:

In this one you can see the engine shaking and hear the diesel-like idle:



This one is at the exhaust - you can hear it smooth out and then start spitting and sputtering:



Where would you start looking?

 

[ColoradoBoy]

I'm just spit-balling, so maybe no help- but I'm intrigued...

Valve adjustment up to date?
How are all the rubber & vacuum bits? Are they warming up & adding un-metered air to the system?
What is the status of the injectors? Could one or two be failing?
Fuel system- pump, filter, FPR, etc?

Good luck- I'll be following along.

 

[Malleus]

If it runs well cold, and then poorly when it warms up, I'd be tempted to look at the throttle body. The IAC valve is notorious for doing exactly what you describe.

It's a PITA to troubleshoot, because there are two checks to make: 1) electrical operation; this is just a "well it moves under power" check. 2) if it passes the electrical check, you still have to pull it out and visually verify that the solenoid is moving all four steps and that it's moving the correct amount each time.

Pro tip: pull the throttle body first. You'll be tempted to try to get the IAC off with it in place, but the lower screw is really long and really stuck in there, and it's a JIS (+) head, so, when you round it off, you have to drill it out, which means the throttle body has to come off. I chased this on my son's 80 for weeks before I found it.

 

[Malleus]

While you have throttle body off, you can clean the bypass galley that the IAC feeds.

The detaila are in the FSM; LMK if you can't find it - I have mine bookmarked for just that reason.

 

[Jeff Elliott]

I'm just spit-balling, so maybe no help- but I'm intrigued...

Valve adjustment up to date?
How are all the rubber & vacuum bits? Are they warming up & adding un-metered air to the system?
What is the status of the injectors? Could one or two be failing?
Fuel system- pump, filter, FPR, etc?

Good luck- I'll be following along.

Thanks -

• Didn't realize valves were adjustable - will need to look into that
• All rubber is new - only thing I can think of would be the brake booster - I will plug that off and see what changes
• Injectors all new about 3k ago
• Fuel pump is original but filter is new as of 3k ago. Haven't looked at FPR - will need to locate that

If it runs well cold, and then poorly when it warms up, I'd be tempted to look at the throttle body. The IAC valve is notorious for doing exactly what you describe.

Will do - thanks for this

 

[Malleus]

The 1FZ-FE valves aren't adjustable. Except when you're building the head.

 

[ColoradoBoy]

The 1FZ-FE valves aren't adjustable. Except when you're building the head.
View attachment 3716768

My bad- I'm lost in 3-FE land, & forget most of you don't have to worry about such trivia!
Sounds like the IAC is the place to start.

 

[Jeff Elliott]

@Malleus I'd sure appreciate that link if you have it handy... This is all going to be complicated by the fact that I'm now turbo'ed. We'll see how it goes.

 

[Malleus]

Jeff, a couple of additional points of consideration worth remembering.

The bore the stepper motor sits in is very close. Any trash in there will keep it from advancing. It can be cleaned with crocus cloth, but be gentle, the bore's a close fit.

Also, the stepper motor position is crucial. It has to be at the bottom of the stroke when the engine's cold. You need to pay attention to how many cycles you run it through, when you're testing it. There are four. The position is stored in the ECU. This is necessary so that the IAC isn't allowing bypass air in the galley when the engine is warm and running the mix too lean.

Pulling the EFI main will reset the ECU and cause it to send the IAC back to the lowest level.

All of this is in the troubleshooting procedure, although it isn't explained, but you're savvy enough to infer what I've explained.

 

[ColoradoBoy]

IH8MUD Resources Menu

 

[Malleus]

This is from the 1995 manual, but the procedure is the same for all 1995-1997.

 

[Malleus]

@Malleus I'd sure appreciate that link if you have it handy... This is all going to be complicated by the fact that I'm now turbo'ed. We'll see how it goes.

I'll take the turbo off your hands, if it's in the way

 

[mudgudgeon]

The 1FZ-FE valves aren't adjustable. Except when you're building the head.
View attachment 3716768

Valve shims can be changed with the head and cams etc in place.

 

[mudgudgeon]

Injectors all new about 3k ago

OEM or aftermarket?

If aftermarket, what brand, and where did you source them.
I know there's fake injectors for sale all over the net.
And some brands are known to be problematic.