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Discussion Starter · #1 ·
I thought I'd make a thread on my fuel injector upgrade I just completed on my 95 Trooper. Disclaimer: Do this at your own risk, check for fuel leaks and do not perform if you are not a competent mechanic. First off, I have put a lot of work in building my Trooper the way I wanted it but am by far no means an Isuzu expert. All I can really share is my experiences working on one vehicle. Second, I put a lot of research in this and I mean a lot. I scoured everything I could find on injectors as well as called different fuel injector specialists around the country. I found discrepancies all over the internet on flow rates, ccs, pounds, and resistance. This info on the net is just not reliable. Period. Thirdly, the beauty of the 95 Trooper SOHC motor and electronics is that it shares a number of parts with the Chevrolet Corvette which helps open the knowledge base up somewhat. The injectors are the same, the fuel regulator is the same, and the coilpack/ignitor are also GM parts.

The stock Rochester Multec 1 injector is a wet coil injector that started in 95 was coated internally to make it less susceptible to damage from ethanol and fuel injector cleaners. The word on the street at the fuel injector service companies is that this didn't help at all and they pitch 60% of them due to failure. This is a 6 hole, 24# injector on the SOHC and is rated at 12.2 ohms. The DOHC injectors are low resistance and this conversion will not work on them at least for 95.

I began with a bosch injector #0280155931 that is commonly swapped on the Corvettes. There are a lot of injectors out there and a lot that are used on the Corvette. This is a 4 hole, 12 ohm injector that the Corvette guys have had good luck with. I did not. It ran alright but I had tipping symptoms between accel and decel which I'm told may have to do with spray pattern or they may be richer than I could confirm and why I'm not listing pounds on this one. Bosch did invent the fuel injector and what's nice about many of them is that the electrical connector plugs right up to stock. Downside, long term safety of install.
 

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Discussion Starter · #2 ·
After being a little disappointed I went back to the drawing board to figure out other options. I thought it might be cool if there was another Isuzu injector that may work, but how would I find the details? Maybe a later 3.2 or 3.5 since it probably would have a correct spray pattern. Also, an ethanol compliant injector was appealing too. Only problem, the plug changed from the stock EV1 to a Multec 2. Thanks to this post, viewtopic.php?f=17&t=66902&start=50, I was able to confirm the 24# stock injector and 24# for all late 3.2/3.5 Rodeo/Trooper (not direct injection). So, a little perusing ebay and I discovered the wiring harness needed to adapt my stock harness to the new injector and after measuring with a caliper it appeared they would be a drop in fit with the late 3.2/3.5 oring kit and even the safety clip might work. Length was perfect so I obtained a set of everything and went to work. And lo and behold, safety clip works and everything fits! The red and black wires were wrapped with cold shrink tape for heat and chaffing protection.
 

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Discussion Starter · #3 ·
These multec 2's tested 13.2 ohms cold and as I was told, better to be a little on the high side with ohms than less as you may risk burning up your ecu. Interestingly enough, my stock Multec 1s had degraded to 9.6 ohms.

Since install, I have noticed consistent cold starts, smoother idle, improved throttle response and no more black smoke at start up from the tailpipe. The motor seems to love the injectors. If I was able to use a scan tool I would be able to check parameters on these to verify what I'm experiencing but so far so good. I'm running some fuel injector cleaner through them since they were used, but everytime I drive it it gets better and better and the ECU appears to be learning through driving and adjusting itself accordingly. This upgrade is really for reliability to get the most out of the motor, not a richer injector or higher flow rate. Time will tell if this works out and it will be interesting to see what my mileage ends up being, but with all my mods I don't expect much.
 
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Discussion Starter · #4 ·
You will notice the offset of the injector is slightly different. It does sit deeper in the hole and is a 4 hole injector. Looking at the head design on my DOHC head I'm running with the SOHC electronics it fits fine and doesn't appear to block flow.

I've had no leaks and the ECU and the Multec 2s appear to be very compatible.

One thing to note, if you try this, I recommend going with new stock plugs as the Multec 1s on these cars seem to slowly foul the plugs over time with a thin coating of carbon that increases the plug resistance by quite a lot.

I'm told if you go too new of a generation of injector it may be too fast for the ECU. I would love to experiment with one of those new 12 hole Denso or Multec 2 injectors as they have the best atomization rate out there, but that's another project for another day.
 

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Discussion Starter · #6 ·
Thanks Brad!
 

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What kind of fuel mileage are you getting? Any change from the old injectors at all?
 

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Discussion Starter · #8 ·
That will take a while to figure out as we normally drive in town and only about 500 miles per month. Pre change, I normally get about 10-11 in town as most trips are less than 3 miles and lots of our speed limits in town are 25. I average about 13-14 on the highway at 75 living in the mountains. Also, notice my gear change, tranny change, and tire change so it may be hard to compare.
 

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Any updates on how these are working out for you? I'm still thinking out a plan to clean/replace the injectors on my 95.
 

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Discussion Starter · #10 ·
I'm pretty happy with mine so far. You could run a tank of Chevron Techron through and see if that helps first. 14.5 mpg on first tank of 279 miles with 120 at 75 mph and the rest in town. 12.5 mpg on second tank at 97 miles all in town, up from my usual 10 mpg. I bought a Tech 1 and when it comes in and I have time to check parameters more that will tell me more.
 

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I have to go in to replace coolant o rings, worn rockers, timing belt, and valve cover gaskets anyway. I'd like to take care of the injectors while it's all apart.
 

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Discussion Starter · #12 ·
Check your rocker shafts. Supposedly Isuzu updated them with improved hardened shafts and that was what was worn on my SOHC heads.
 

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I've got a pair of heads from a 95 sohc that was rattle free. Mine is quite noisy and seafoam treatments and rotella made no difference at all. So I figure worn shafts and rockers both are likely.
 

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Discussion Starter · #14 ·
2 more tanks have yielded surprising results. 1st tank around 280 miles, 120 on highway and rest in town low speed, high stop and go, 14.7 mpg. 2nd tank 210 miles, 125 or so highway, but going hard over 4 mountain passes with the rest in town and sitting idling 15 minutes +, 14.1 mpg. I'm very pleased with these numbers. Hopefully my new bottom out mpg will be 14. Pretty good being that I live at 4900 feet in a mountainous area and that I have not seen these kind of numbers in years.

I've been playing with my recently acquired Tech 1 scan tool and am noticing that my motor is running on average about 189 degrees. My factory service manual says that the ECM does not lean out mixture to normal on warm up until the motor hits 201 degrees. Being that the factory thermostat is a 170, I ordered the only alternative temp I could find that is a 180 and will experiment to see what the Tech 1 says. If anyone knows of a higher temp thermostat for this motor please post where to find it. Thanks.
 

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Hmmm, that's interesting !! Water does boil different at higher altitude , you wouldn't ever really take those statistics and consider them with a vehicle but maybe your on to something...
 

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mtman said:
If anyone knows of a higher temp thermostat for this motor please post where to find it. Thanks.
Could always go the route of removing the t-stat from the engine t-stat housing and get an inline housing and t-stat to plumb in the hose between the engine and the radiator.

edit: here is a quick search link to jegs, they have a high flow 195 for said housings http://www.jegs.com/webapp/wcs/stores/s ... e+Housings
 

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Discussion Starter · #17 ·
That's a cool idea. I hadn't seen it before.

I installed the thermostat. That Stant just doesn't look as heavy duty as the Isuzu brand, but I don't know how to get a Japan made one that's hotter.

Anyways, pretty hard to get the motor up to 201 degrees. Maybe after it bleeds out some it will stabilize and do a little better. It was running between 191-203. I was able to get it up there a couple of times, but the air/fuel mixture never adjusted to 14.7:1. This is a total learning curve.

I will say by feel though, the motor seemed a lot happier running hotter. The idle is basically perfect at around 201 degrees now.

I've heard that engines are the most efficient around 201 degrees. I don't know if that was true in 1995 or if that is more a function of the dumbed down gasoline we have today. Or maybe things have to be more precise today with our gas. I just know somewhere around 2004 my mpg's dropped and the motor didn't seem that happy anymore. Isn't that the time that fueleconomy.gov lowered all the mpg ratings on cars? Hmmm.

I'm going to drive it like this for awhile and see what happens. The engine certainly seems happier.
 

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You already replaced the ecu temp sender a while back correct ??

What's your afr been ??

If by chance you have an adjustable fpr you could lower it a lb or two, That would help..
 

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Discussion Starter · #19 ·
I've replaced the temp sender for the ecu. The afr is a hair rich at 14.6:1. The Long Term Fuel Trim is about 105 with the stock 170 thermostat and about 110 with the 180. It should be 128. I've been told by an Isuzu mechanic that Troopers tend to run rich by the factory tune so those numbers are probably inline with the factory tune. Considering an adjustable fuel pressure regulator.
 

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This is looking more and more like the way I'm heading with replacing my injectors. It sounds like you've made definite improvements, even factoring in all the other mods your truck had compared to mine. I am lucky to get 12MPG with my stock 95.

What tech 1 scan tool did you get and are you happy with it? I've been looking at a few but there are a lot to choose from.
 
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