TOPIC: Isuzu 2001 dualcab 2wd 3.2l V6 Petrol hungry. Need some hope!

Thankyou Ron, Greg, Kman and Tracy,
I got a rush of motivation and mistakenly thought I had resolved the Speed sensor check engine light by replacing the sensor, but having taken the first step is one less to do. I found a fault in the harness - drove 35kms and back on again! Done some more volt drop checks etc following troubleshooting guide and think I am about up to step "replace ECU". I have a faulty spare/original ECU so will try and get it repaired....
Anyway back to other progress.
1. Waiting for 32mm oxygen sensor extender to arrive.
2. Ron, I will recut the groove using the large cutter (now I found it again!) cos current groove used the middle sized bit. Can you please comment on whether I have messed up putting a second groove at the top of the throttle plate? I cut 1 groove at the bottom and another at the top. I realize less air goes over the top of the throttle plate but thought the smaller amount of air that gets over the top can go over a groove too??!? Maybe just enlarge the bottom groove and leave the top alone?
3. I am going to run max tyre pressures and also go back to standard 205 tyres, cos 225 tyres might also be using some fuel.
4. Hot tip! Some Bosch oxygen sensors don't have external ports and use the length of wire on their harness as "ports" so it is critical to never cut the wires on these oxygen sensors! A friend in the trade once did a Bosch training course and the trainer confirmed this to him.
5. Open the spark plug gaps.
Greg, I haven't really noticed much change yet, the car is new to me and only done about 3,000 kms in it. I had cut the groove and blanked pcv etc before I drove it properly too. To me the motor seems very smooth and quiet. Apart from how much fuel it has been using I really like the vehicle. I fitted new rear shocks last night so hopefully Ill enjoy that difference too. I live in the country, so I either do very little distance or a lot when I go somewhere, I will be away for some work and will be doing more than 600kms over the next 4 days. Ill be measuring mileage accurately!!
I feel quite confident I am going to have success on this vehicle (unlike a few rushed attempts in the past) so looking forward to more playing. If needed I will attempt to corrupt the airflow meter if I have to.
Kind regards to all, Neil

If you're a fan of Star Wars, and have watched the Disney+ series The Mandalorian, remember this line: "This is The Way."
I'm still very certain that you'll see gains, given what you've written already. There is a proven method to our process.
Right now, I doubt the computer is in a place that it can learn new things and give you better mileage/consumption moving forward, based on this last post. I appreciate your enthusiasm and take-charge attitude, but wouldn't it be simpler to fix the wiring harness? Have you considered that part (or worse: most!) of any computer "problems" might be from the tire size being not what the ECU is expecting? Your odometer/trip meter is incorrect, the speed sensor is sending data to the computer that it quite likely is interpreting incorrectly.... take care of these, and use your 600km trip driving to establish a baseline for gains moving forward with o2 extenders and the regroove and opening up the spark gap.

Hi Greg,
Thanks heaps for the thought about tyre sizes confusing the computer! never thought of it, although not sure it is possible but I will eliminate that possibility. Surprisingly, Its a fairly simple commercial vehicle, 5 speed manual, has no ABS, air-bags, cruise control etc.
1. As far as I know the wiring harness is now perfect, I have completed the troubleshooting steps (bar one that I need another tool to complete a step) to pretty much narrow it down to a faulty ECU (even cleaned all the earth terminations).
2. I am now waiting for the o2 extenders and spark plugs to arrive.
3. I am hesitating on the re-groove because not sure if I've messed it up with cutting the second groove up the top (what do you think). At a guess I should just leave the top alone and re-cut the bottom groove to the largest cutter size?
I am planning to do everything by the book, using gadgetmen advice. Ideally I would have waited until I addressed the engine light/code.... but was multi-tasking.....shouldn't have I know, since I'm not a woman Lol!
Kind regards, Neil

Leave the upper Groove as is and just use the lower Groove as the guide for the larger bit to enlarge it.

If you’re sure about the ECU, change the tires and spark plugs and extend the o2 sensors out of the exhaust pipe, re-condition the existing computer and let us know what the results are.

Neil, please post pics of yours work here!
Once attached, "Insert" them into the message so everyone can see. BTW, I now see over 5,000 GUESTS per HOUR are coming here for advice! So, rest assured people are looking at US as Experts in the field!

Way to go, guys!!!

Couple things I'd like to add here. First: Neil, if you can get any pics in here of your Grooved throttle body, it could help us w/ details of that Groove work. I or others just might spot something or give advice to help.

I've not yet used O2 sensor extenders, though I see the potential benefit. The exhaust gas stream will be slower moving/denser against the inner wall of the exhaust pipe, and the idea is that the O2 sensor tip will be placed into a "richer" area of the exhaust gas stream. Makes sense to me. As Kman says, a bit of anti-seize compound on the threads will save grief down the road. I just imagined a method of "tuning" this O2 extender idea.

Take a 6 inch long section of exhaust pipe with an O2 sensor bung welded in the side, with the hole thru the bung into the pipe. Now you can screw into place the O2 sensor and different O2 extenders. This allows adjusting how far into the inside of the pipe the O2 sensor tip is placed. Best practice would be to use the same O2 sensor from the vehicle in question, and try different extenders to try to get the sensor tip as close to the inside wall of the pipe as possible.

Someone correct me if I'm wrong here- but I'd think you don't want the O2 sensor tip withdrawn out of the pipe by using an extender too long or deep. But, ideally, the sensor tip poking in enough to expose it to exhaust gas, but out of the center of the pipe I.D. In other words- as close to the pipe inner wall as possible, into the slower moving/denser-or "richer" flow region.

I dunno if this idea is original, but it could be useful...?

Tracy G

Yes indeed TracyG, the short extender (I believe it was around 32mm, or 1-1/4”) is what would probably work best from where I sit because it would just pull the tip of the sensor out of the exhaust stream and create a nice pocket of rich exhaust byproducts in the downpipe from the manifold to the converter...but as Ron said, pictures are worth more than the proverbial 1000 words.

Hello everyone,
two photos below. One is of the small groove before I re-cut it to the large size, the other photo is of the new large size groove. The hex drive plug is visible threaded into the IAC port. I fitted new spark plugs gapped from their standard .044thou out to .050thou now. Car is running fine so looking forward to an economy test drive. Last weekend did over 700kms averaged 12.8 litres per 100kms.....lots of room for improvement
Kind regards, Neil

Both cuts look.good! I am looking forward to your mpg and power gains. Keep on brother!

Economy so far. I have just done a bit over 500kms this week and averaged 11.8 litres per 100. Down from 12.8. Power seems to be the same, exhaust seems cleaner (can't smell so don't know if smell is different) and there is a very different bark to the exhaust note at 5000 rpm!
Two questions
1. The vehicle stumbled on take-off a couple of times but only when cold. Is this what happens with excessive spark plug gaps? Mine are at .050 thou. Seems a very wide gap to me..I think I need to close it up a bit. Can I please have any help on this. The factory gap is 1.1mm, or .044 thou. Has coil over each plug.
2. I am becoming aware of more and more things I can do, and I do want better than 11.8 combined economy. I have seen comments about baffles being problems inside the intake manifold. This one can unbolt the top half. Is there any benefit in opening up my spare intake manifold and investigate removing cast aluminium baffles?
Thanks again to everyone, Neil

Spark plug gap: consider that it takes a slightly longer amount of time for the energy discharge to happen with wider plug gaps; yes they’re only tiny fractions of an inch difference, but that extra time to travel the extra distance (even at the speed of light!) translates to a retardation of spark timing. Unfortunately, that timing is controlled by the computer rather than distributor position with vacuum advance. Look into how your engine determines appropriate engine timing, what sensors it uses, and determine how changes to the signals of those sensors are interpreted by the computer. A lot of people (including myself) have had success with a MAP enhancer circuit that I found described on George Wiseman’s Eagle Research website.

As far as the intake manifold...well, you’re the expert on this engine around here. What do you think you should do? ?

I could tell something was happening after installing the Groove when I realized my exhaust note at idle was lower/deeper. 5000rpm - do you get up into that range often? That might have something to do with the consumption numbers you’re reporting ?

Thankyou for your thoughts Greg,
Spark plug gap: I will try and check out that George Wiseman website (I am not great on computers and struggle for good internet reception where I live). Sounds like you are pretty comfortable with .050 thou plug gap. I can notice multiple differences from the groove so I am comfortable with your notion that the timing is now inaccurate enough that it affects low rpm acceleration when cold.
Intake manifold: I have no idea. But I have read many posts and Ron has spoken of the negative influence of baffles upon the groove, I was just wondering if less baffles is always better? There is a common engine I hear about that has long/ short runners used for low/high rpm controlled by internal baffles switching it, and controlled by the ECU. A respected engine tuner insists that these are a waste of time. Seems possible to me that if Ron dislikes baffles there might be some history of removing them for beneficial gain.
RPM. It truly is amazing to hear the difference in the motor after installing the groove (bring on the economy tho) in the exhaust note and other things. I only did 5000 rpm briefly to listen to how the motor sounds....red-line is 6000 on this motor...never been there!
Kind regards, Neil