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Discussion Starter · #1 ·
Hi, I need help. I have a 1999 Trooper. Back in April I replaced two of the ignition coils after the check engine light came on. Also cleaned the ERG valve. (I'm not actually doing this work, but a friend is doing it for me. I'm doing all the research.) The vehicle ran ok, but not perfectly until about a week ago when the check engine light came back on. Replaced another ignition coil, but this time the cel came back on. Took it to Autozone and they said the codes indicated it needed spark plugs. They gave me Bosch Platinum, said they were best for my vehicle. Changed the plugs, a couple trips (that same day) later cel back on. The cel came on after the car engine surged high and low, just once on start up. I've noticed the surge for about a week. Not horrible, but noticable.

Now I started reading on line about ignition coils and there is some discussion about a change in July 1999 and that now there is a 5 pack for all coils except for the one cylinder 6 coil that is separate. This is the first time I read that. I got the original coil from the Isuzu dealer and they tell me that the part number is the same for all 6.

Can you guys help me? I also read on this forum that the Bosch plugs cause the cel light to come on. That may be the case, but there is something else wrong here. The vehicle runs better but not perfectly. I figure that since the first coil needed replacing last April that the rest must not be far behind and need replacing too. I was all set to order the rest of the replacements until I started reading that I might need this 5 pack and the separate one for the 6th cylinder.
The person helping me is good at actually doing this kind of work. Not a mechanic but he has patience and does his own work. But he doesn't know anything about the Trooper. So, what can you suggest in terms of articles, guidance, your own wisdom.

Thank you all for your help. :D :shock:
 

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Discussion Starter · #3 ·
I have just over 70,000 miles. Never had work done to the manifold gasket. I've read about it though, and I haven't heard a hissing sound.
 

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I think the problem with the Bosch plugs is for 2000+ models that use "ion sensing"...in any case based on your symptoms I would not suspect the plugs, I would pursue the intake manifold gasket idea. You can't always hear it; on my 99 Trooper the IMG went out twice. The second time I could hear the hissing, but the first time I couldn't hear anything. The nice thing is it was under warranty so I had no problem taking it to the dealer for diagnosis...
 

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Discussion Starter · #5 ·
Hi, thank you, I will look into the Manifold gasket idea. Does anyone know anything about the ignition coils? I called the Isuzu dealer and they said all 6 had the same part number for my vehicle. But, I've read something about a change in July 1999. I need to know since I'm probably going to buy the rest of my set of six soon. What I've read said that cylinder 6 uses a different ignition coil. Don't want to use the wrong kind. I imagine that would cause some kind of problem.

Would it be useful, do you think, for me to buy a code scanner?

Thanks,
 

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dianewong said:
Hi, thank you, I will look into the Manifold gasket idea. Does anyone know anything about the ignition coils? I called the Isuzu dealer and they said all 6 had the same part number for my vehicle. But, I've read something about a change in July 1999. I need to know since I'm probably going to buy the rest of my set of six soon. What I've read said that cylinder 6 uses a different ignition coil. Don't want to use the wrong kind. I imagine that would cause some kind of problem.

Would it be useful, do you think, for me to buy a code scanner?

Thanks,
Why would you replace coil packs that haven't gone bad? I have had to replace one coil pack in the 8 years I've had my Rodeo and at $100+ each there's no way I would shell out the $600+ to replace them just for the sake of doing it.
 

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Replacing coil packs is very, very rarely needed. To need more than one is unheard of in my experience. If you really suspect a coil problem try swapping them around next time to see if the problem moves. If not then look elsewhere for your problem.

The coil pack for cylinder 6 for a 1999 Trooper does indeed have a different part number. This came up maybe 6 months back when someone else posted this. I have access to a parts manaul and looked it up to verify. But like I noted I really doubt you have a coil problem.

I personally would only use the manual specified Champion or NGK plugs for any Isuzu. That being said I doubt Bosch plugs would cause a CEL just that they might result is a very slight mileage and performance hit as I doubt they are finely tuned for the Isuzu engine.

You could buy a code scanner. Harbor Freight has one for about $40 when it routinely goes on sale. It all depends on how much trouble it is for you to get the free reads at Autozone.

As for cleaning the EGR, this can be a good preventative maintenance step if nothing else. Just make sure the return tube is also cleaned as it if is plugged cleaning the valve will have no effect.

Based on the limited description of your problem (you spent most of your time describing the attempted fixes) I am guessing IMGS. Your mechanic friend should know how to check for a vacuum leak.

If you really want some more informed help then post back with the exact codes you are getting and more info on any drivability issues. Other than that we are all just guessing as to what the real problem is.
 

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Discussion Starter · #8 ·
Hi, I have some driveability info.

Took it to Autozone. These are the codes: PO174 The fuel system for Bank 2 was too lean, and PO304, misfire in cylinder 4.

The problem is that there are occasional surges in rpm when in low idle and sometimes when I first start the Trooper The surges seem to cause the CEL to come on. The surges don't occur all the time but when they do and the rpms go way up and drop down low, then I hear a click and the CEL comes on These days the vehicle is commonly idling at 500 rpm.

Other than that, the vehicle runs pretty smoothly.

I appreciate your help and patience.
 

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Definitely sounds like the common intake manifold gasket problem to me...and as I said it went out twice on my 99 Trooper so I've been there. Don't chase those codes, in this circumstance they are deceptive because the engine is not getting proper vacuum due to the intake leak, so the engine computer is struggling to compensate, resulting in idle surging and all the OBD II codes that are two steps removed from the actual problem...
 

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Discussion Starter · #10 ·
Hi, thanks for your help on this.

Got the intake manifold gasket changed on the '99 Trooper
Started out on a test drive and it was still running rough like a misfire, just as before (originally we took it to Autozone and the code said misfire at cylinder #4.) Stopped and upon restarting the engine surged high up to about 1800 and immediately dropped low, maybe 1000 rpm. It did that a few times and the cel came back on.

The Trooper runs ok after start up. The misfire is noticable only when it idles. Sometimes when it starts up engine surges wildly high and then low, up and down. It doesn't always surge, about 1/2 the start ups it surges. But the idle is constantly lower than usual. Before the idle was at about 750 maybe 800 rpm, now it stays at about 500.

Before we changed the intake manifold gasket, we tried the test of spraying carb cleaner around the intake manifold area. It did just as has been described, the engine surged. So, we got the gaskets changed, but the Trooper is running exactly the same as before.

Does anyone have any ideas about what we might try next? Thanks everybody for your help.
 

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How many of the IMGS (yes there are more than one) did they change?

Have you repeated the vacuum leak test?

Point being maybe they only replaced one IMG and/or didn't do the work properly. That or maybe they forgot to hook up something they unhooked during the IMG work. Thus, I am recommending your thoroughly recheck the work they did before looking elsewhere.
 

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Discussion Starter · #12 ·
Thank you Tomster, will call for the recheck. They changed both sides though. Will repeat the vaccum leak check and will check the IMG for proper installation. Thanks
 

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Its more than well discussed how the 98-up Troopers really are picky about plugs.

Go to the dealer (or call st. charles) and get the right plugs.

They aint cheap, but cheaper than fixing stuff that aint broke.
 

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Discussion Starter · #15 ·
Hi everyone, still having the same problem with the Trooper.

Rechecked the IMG installation and it seems to be fine. Retested the spay with carb cleaner, the engine still surges.

Went to auto zone. Throwing code 174 showing misfire in cylinders 4, 5, and 6. Too lean, not getting fuel. Same code as before.

The Trooper does not surge when the vehicle is cold, but after you drive it and its wam, when you shut it off and restart it will surge high and low as much as up to 1800 drop to 400, then back to 1800 and down to 200 where it will cut off. If you catch it before it stalls and hold the gas pedal down for about 20- 30 seconds it will smooth out and not surge again until it restarts (when still warm). Could it have to do with the injectors or the fuel filter? Thanks for any help.
 
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