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Old 07-29-2020, 07:51 PM #16
pinemind pinemind is offline
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Exclamation

I think, it's finally f@#$%ing fixed. Let me be clear: I haven't nailed down what fixed it but I'll explain below.

What do I mean by fixed?
- The random misses at warm idle are gone. I ran it for about 5 miles (it was already warm), then sat there for 30 minutes with my timing light tach adjusting the idle screw to nail down 750 RPM.
-The idle RPM range is now 10 to 15 in fluctuations (i.e the extremes it will hit will be 745 and 755, but mostly stays in a 5 RPM range). Before, it was easily a 50 RPM extremes fluctuation, sometimes 60.
- My gear knob, the ultimate indicator, now does not have the violent shudders randomly to match the put-put, put ... put's out of the exhaust.

What did I do to fix it?
1. I ordered a Denso 1 wire o2 sensor to take my heated 4-wire out of the mix, soldered in a longer wire, and hooked it up. This did not make a change. I did have to run it a bit since it's not heated as I took out the EFI fuse to reset things. But once it was warm, the misses were definitely still happening. I left this in there for now (more on that later)
2. The broken pulsation damper - As stated above, I noticed it was missing a screw. Normally this only exhibits problems on acceleration and not at idle from what I've read. But, seeing as it has been the ONLY BROKEN PART in the entire EFI system (as you know everything else tested out fine regardless of me replacing it all), I ordered an OEM one. I put this in and had to run it a bit to get the shakes out (not quite sure why). Went around the block a few times and as I mentioned above, sat there with a tach for 30 minutes. No more misfires and the tighter idle RPM fluctuation. I am claiming victory as this problem would always manifest itself at idle within 30 seconds of stopping. Through all my changes, when I thought I fixed it, it would come back within a minute or 2 of stopping.

So ... damper or o2 sensor? I'm going obvious on this one and saying it's the damper. It was freakin' broken and I replaced it last! No mention on any thread that the fuel damper has ever caused erratic idles, it's always the FPR. I will put my heated o2 sensor back in, since it should be there and will need to be there in the winter. I'll be trying this out tomorrow morning once everything cools. Once that's done, back on goes my OEM distributor, OEM AFM, and OEM FPR (well, not the FPR, I'm done taking the plenum off for the 1000th time for awhile).

But for right now? Victory lap and a beer

I'll update tomorrow when it breaks again ... no ... positive thoughts ... I mean, when I confirm it was the damper Sorry, bad habits die hard.
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Old 07-30-2020, 08:25 AM #17
pinemind pinemind is offline
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Not fixed, kill me.

Swapped back in 4-wire heated Denso o2 to get it back to original configuration. Misfires returned (pulled EFI fuse before for 15 min) even after driving around for 20 minutes.

Hoping it was the o2 sensor, put in the new 1 wire Denso I had it when I "thought" it was fixed ... misfires.

Interesting data points:

- After putting in the 4-wire this morning, and driving around, the idle was low (650 RPM). I left it last night with the 1-wire and it was right around 750 RPM. So I had to adjust the idle screw to get it back up to 750 ... weird.
- When I unplug the 4-wire o2 sensor once it's warmed up, the idle raises to about 900-950 RPM and the misfires are basically gone.
- When I unplugged the 1-wire o2 sensor, no change in idle, no change in misfires. So it's in open loop, not throwing an o2 code on a brand new sensor, assuming it's reading the o2 sensor fine, and misfiring. I guess back to the fuel injector theory or leaks (vacuum or exhaust).

So what happened last night? I have no clue. What I didn't test last night was pulling the o2 sensor connection with the 1-wire while it was idling properly. My guess? It would not have changed.
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Old 01-16-2021, 03:10 PM #18
HulkHagan HulkHagan is offline
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Hey Iím so sorry to hear about your issue. I was reading on other forums that this problem can commonly be traced to a vacuum leak in the brake booster diaphragm. These old boosters tend to fail so it may be worth swapping it out along with the booster vacuum line. You can test your brake booster for a vacuum leak by pressing the brake pedal all the way down with the truck running, and then shutting it off. It should allow you to continue pressing for 30 seconds, but if itís bad, it will force your foot back up pretty quickly. Thereís a valve on the booster that you can test as well, where the vacuum hose attaches. It should only allow air in one way. From what Iíve read though, the booster diaphragm is the more likely culprit. Best of luck!
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Old 01-16-2021, 03:13 PM #19
HulkHagan HulkHagan is offline
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Also, Toyota doesnít make these boosters anymore so youíll have to get an aftermarket one. I wouldnít trust an old one even if it is oem. People tend to like Napaís though. Also, you can do a direct bolt on of a T100s brake booster. Itís a bit thicker so it will give you better braking power supposedly. Iíd go to Napa and ask for a brake booster without ABS for a 96 T100 4wd.
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Old 05-21-2023, 03:05 PM #20
Jram100 Jram100 is offline
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Reviving this thread. Obviously a very thorough search for a solve to this problem.

Experiencing the same issue, Did you ever find the gremlin responsible?
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Old 07-09-2023, 05:42 PM #21
Pavehawk86 Pavehawk86 is offline
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Ditto! Has anyone figured this out??
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