1997 1FZ Hiccupy idle and running rich (1 Viewer)

Joined
Apr 11, 2019
Messages
323
Location
NJ
Another thought for this topic: condition of the crank pulley (harmonic balancer). Have you inspected the rubber on it for cracking and signs of fatigue/failure?
 
Joined
Feb 12, 2015
Messages
92
Location
Plano, TX
Another thought for this topic: condition of the crank pulley (harmonic balancer). Have you inspected the rubber on it for cracking and signs of fatigue/failure?

I have not, but damn if this isn't moving to the top of the list. If so, is the fix just "a new HB" ? I'm not sure I have the equipment to hit 304 ft. lbs. of torque.
 
Joined
Apr 11, 2019
Messages
323
Location
NJ
Take a photo of the front face of it for us to see. Cracking on the rubber ring is an indication of age though it may be difficult to see. Heat and oil leaks don't help with rubber components.
You could also, carefully, pry with a lever arm between the pulley and engine. If the pulley moves easily then that's another indication of fatigue.
 
Joined
Jan 17, 2017
Messages
381
Location
PNW, USA
Following as I have a slight periodic something or another while sitting in the seat though it sounds perfect in the engine bay I can feel the vibrations.
 
Joined
Feb 12, 2015
Messages
92
Location
Plano, TX
Following as I have a slight periodic something or another while sitting in the seat though it sounds perfect in the engine bay I can feel the vibrations.

Bingo! Mine is more rhythmic than periodic, but it is so slight it doesn't shake the truck or register on the tach, can only slightly be detected in the engine bay - it is almost purely a "seat feel" thing.

I am just baselining and trying to make her dead reliable so I can take it all over this coming year. And not having a long history with the truck, I want to hunt down everything that could use doing, within reason. She's otherwise such an honest rig, some TLC is well-deserved.
 
Joined
Feb 12, 2015
Messages
92
Location
Plano, TX
Take a photo of the front face of it for us to see. Cracking on the rubber ring is an indication of age though it may be difficult to see. Heat and oil leaks don't help with rubber components.
You could also, carefully, pry with a lever arm between the pulley and engine. If the pulley moves easily then that's another indication of fatigue.

I couldn't get my phone in there with enough light by myself...and it is raining out. Maybe I can con, I mean, coax the wife into helping when she gets home. 😄
 
Joined
Feb 12, 2015
Messages
92
Location
Plano, TX
I couldn't get my phone in there with enough light by myself...and it is raining out. Maybe I can con, I mean, coax the wife into helping when she gets home. 😄

@logicbyondreaso - It has been chilly and rainy all weekend, so it took me several tries to find a dry spell + “successful” attempts to photo/video.

Here’s a decent shot - it’s the narrow ring of rubber I’m looking for, correct?

09AEA78D-F457-469A-A3D9-216F4EFE0F03.jpeg


I also took a video but need to upload it to YT I guess.

It doesn’t look overly wobbly or anything...belts don’t seem too tight.

Thoughts?
 
Joined
Apr 11, 2019
Messages
323
Location
NJ
Great photo and video. Nothing stands out visually. Engine looks to be very smooth and no visible vibration. The only thing I can say is that as durometer of the rubber changes from age, oil, and heat - the frequency at which it's supposed to function will change as well. This means it's no longer doing the job it's installed to do. Before you go replacing the pulley, try some of the other members suggestions.
 
Joined
Feb 12, 2015
Messages
92
Location
Plano, TX
Great photo and video. Nothing stands out visually. Engine looks to be very smooth and no visible vibration. The only thing I can say is that as durometer of the rubber changes from age, oil, and heat - the frequency at which it's supposed to function will change as well. This means it's no longer doing the job it's installed to do. Before you go replacing the pulley, try some of the other members suggestions.

Thanks for looking at this for me! It has been about 5 years since I had a 1FZ and so I don't have an innate sense of what's normal, yet. Noted about aging = slow degradation in performance over time.

Latest update - I was too beat to do this last night, but here goes.

My parts from TPD arrived and I did a new cap and rotor, which was straight forward and less than $30 - after comparing the used vs. new part it was definitely time. I am now wondering if it isn't time for a new set of wires too, as they are at least 10 years / 60K miles old.

Hooked up the Ultragauge and configured it to display Temp/RPM/ST fuel trim/LT fuel trim/and both O2 sensor voltages - and TPS % and Timing Advance.

Since the first path I started following was vacuum/EVAP - I expected to see LTFT +10-15% - meaning it is trying to compensate for the unmetered air by adding more fuel. I found the EXACT OPPOSITE.

At warm idle I was seeing between 1.6-3.2 negative LT fuel trim - meaning it is detecting a rich mixture and pulling the base map back about 3% or so. Slightly leaky injector? But I would expect this to have some sort of negative effect on fuel economy, and I am not seeing that at all.

I also watched both O2 voltages fluctuate between 0.1 - 0.9, and the STFT moved opposite the O2 sensor voltages.

I took it out for 25-30 miles of mostly highway, but some city driving as well, logging MPGs, watching these other values, etc.

By the time I was heading home my average MPG on the highway was 15.4 AND CLIMBING.

Brand new the city/highway on these are rated 13/15, so 15+ average on the highway is phenomenal, right? I was seeing instantaneous MPGs at 65-80 mph in the 18-19+ range, and even spied a 29.0 at some point with the throttle at about 5-10% off idle.

This seems to eliminate a massive vacuum leak...or even a small one at this point.

I will say this - after it was good and warm - 190+ and I had been flogging it - it seemed much much happier - the lumpy idle/seat shake was almost gone at one point. It runs very cool - on the highway at 80 I saw 183-185 pretty consistently. Is it running too cool?

I am running a tank of premium through it right now with a Lucas Injector Cleaner additive in the mix.

So, what next?

  • EGR stuck slightly open/not closing consistently, letting exhaust gas pass into the intake at hot idle? (this seems to fit the negative FT at idle fact pattern)
  • TPS misadjusted? (reading with no throttle pedal was 10.2%, but it isn't an absolute zero when the throttle plate is closed, but I don't know if this is too much or not)
  • IAC gunked up and/or INOP?

I have also thought that since it might be one of the oddball engines that wants a little more timing advance to be happy/smooth at idle, but I want to do that dead last so as not to band-aid over a real problem. Some have suggested this - and it seems to be a case by case basis as to whether the engine will tolerate it.

I did notice that the ECU was adding 3.5-5 degrees (average 4) of advance on top of the 3 degress mechanical advance. Since the FSM says the total advance at warm idle is between 2-13 degrees, it seems to suggest that I could add up to about 5 degrees of mechanical advance and still be within the FSM range. What say you, @mudgudgeon ?
 
Joined
Feb 12, 2015
Messages
92
Location
Plano, TX
If you haven’t replaced the O2 sensors I’d do that. I’ve been using the Denso parts for this for a while.
Front O2 is OEM and 60K miles/10 years old. I think the rear is original...so 250K/24 years

Definitely on my to-do list. Are there ways to test them to see if they are good? I didn’t see anything in the FSM, but it’s not always organized and indexed how I would expect

I’m so far down the rabbit hole on this that I don’t just want to keep guessing and hanging parts.

The stellar MPG and +/- 5% fuel trims seem to be telling me I’m super close.

I wish I could EGR delete this so badly.

This was a note the PO left in the FSM:
3410A021-EF7A-4735-ADEE-4AE0A5A5A388.jpeg
 

landtank

Supporting Vendor
SILVER Star
Joined
Mar 27, 2003
Messages
20,047
Location
Groveland MA
I’ve had them drift and on my first 80 I was getting unusually good fuel mileage for a while and they then gave a heater error and once replaced my mileage was back to normal. I change them out as part of my base lining. The EFI system relies solely on the O2s being accurate. If they aren’t the the ecu will just make adjustments to get the signals from the O2s it’s programmed to see. So it’s possible to run rich or lean and the system thinks everything is fine. That’s why it’s important to stick with factory parts here. Dropping in anther brand could introduce a problem that the ecu would be blind to. When I first used Denso brand I monitored the exhaust with a wide band to confirm proper operation.
 
Joined
Feb 12, 2015
Messages
92
Location
Plano, TX
I’ve had them drift and on my first 80 I was getting unusually good fuel mileage for a while and they then gave a heater error and once replaced my mileage was back to normal. I change them out as part of my base lining. The EFI system relies solely on the O2s being accurate. If they aren’t the the ecu will just make adjustments to get the signals from the O2s it’s programmed to see. So it’s possible to run rich or lean and the system thinks everything is fine. That’s why it’s important to stick with factory parts here. Dropping in anther brand could introduce a problem that the ecu would be blind to. When I first used Denso brand I monitored the exhaust with a wide band to confirm proper operation.

It doesn't seem very resilient - fuel trim is less than 5% - anything more modern/sophisticated and it would be imperceptible to the driver.

Denso O2s - looks like p/n 234-4153 (downstream) and 234-4157 (upstream) - does this look correct to you?

How does an aging/unknown MAF play into this equation? I know we have already PM'd about me grabbing one of your MAFs once they are back in stock - please allocate one for me.

Also, how does the theory of a slightly stuck open/leaky EGR valve allowing exhaust gas into the intake when it should not square with you?

Sorry for peppering you with questions man.
 

landtank

Supporting Vendor
SILVER Star
Joined
Mar 27, 2003
Messages
20,047
Location
Groveland MA
I was focused more on you thinking you were running rich and the fact that after pushing the truck some it seemed to be running better. As far as the little stumble at idle, that could be a MAF sensor. I started including air straighteners with mine as there was a noticeable improvement on signal stability at idle afterwards.
 
Joined
Feb 12, 2015
Messages
92
Location
Plano, TX
I was focused more on you thinking you were running rich and the fact that after pushing the truck some it seemed to be running better. As far as the little stumble at idle, that could be a MAF sensor. I started including air straighteners with mine as there was a noticeable improvement on signal stability at idle afterwards.

Good deal. Looking forward to getting your MAF installed as well.
 

Users who are viewing this thread

Top Bottom