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Discussion Starter · #1 ·
first off, I'd like to say that this is a great site and I'm glad that I was pointed to it.
I just came in possession (long story) of a 92 Isuzu Pickup 2.3L, manual transmission, carbureted, 115,000 mile base model, no frills el-strippo. I kinda like it.

I'm currently having a problem that I've seen in a few posts here, but I want to get a diagnosis anyway. The truck runs fine in the morning for about 8-15 miles of my morning drive, then it will start running really rough. The idle has never been great but it will stutter very badly leaving from a stop. It takes a heavy throttle to get it going. Then at the bottom of each gear it will stumble badly, and cruising around 55 MPH in 5th gear, I can feel it missing.

I replaced the vacuum lines, which is a task unto itself (there's a ton of those things) and that didn't really help, but they were cracked and needed replacing anyway. Some posts i've read in my search indicate the Oxygen Sensor might be shot. Since they're cheap, I may go do that this weekend, along with the PCV.

Am I on the right track or does anyone have any better recommendations? Any help that can be provided will be of great value.
 

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I don't suspect the O2 sensor, but they are cheap. Isuzu wants them replaced every 90k miles. It sounds like a vacuum leak. While you are playing around though you should change the distributor cap and rotor. Be sure to get one that doesn't say ITALY inside of it. There isn't one brand (Other than OEM) that always has non-Italian made caps. For some reason the Italian ones don't last very long at all.

I'm not sure that the carb'd engines have an o2 sensor though now that I think about it. I'm not sure what the sensor would be used for.

If you feel excited, adjust the valves. They are supposed to be done regularly (either 15k or 30k miles - my memory of the 2.3 is a bit fuzzy) and if you don't know the history they are due.

Good luck,
Tad
 

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It also sounds like it could be water in the fuel. Usually that goes away after a while and is not so predictable. Might be that it just comes up when you hit a particular incline and water in the tank hits the pickup tube.

You could have a vac leak in something thermally controlled like the EGR, the flapper valve in the horn of the air cleaner, or maybe the mixture control valve. The MCV can leak a huge amount of vac off, it is the barbell shaped deal on the passenger inner fender that has a 1/2" hose hooking it to the intake. You should hear it hissing if it has gone bad. You could try blocking off the large port to it and see if that helps though. The air cleaner just block off the line to it at/near the intake and see if that helps. The EGR is a bit tougher, but you could bypass it to eliminate it.
 

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Discussion Starter · #4 ·
I'd like to t hank everyone for their input on this, it was very helpful.
This morning I went out and changed the O2 sensor and the PCV valve, as well as replaced another vaccum line I found and tightened up the Alternator bracket, which was very loose for some reason. I took it for a short test drive and it sees MUCH happier now. I won't know for sure until I take it out for a longer drive, but I have a good feeling.

I think the O2 sensor (there seems to be only 1, located in the collective point of the exhaust manifold) was probably the stock unit, and the PCV was clogged when I took it out...I couldn't blow through it. I tried again later and was able to, so I'm not sure what the story is there.

So, we'll see what happens, but Thanks everyone. I'm sure I'll be posting more here as I bring the little beast back to life, and my sick desire to make everything I have a little faster than it should be...I don't know why I do that.

Thanks again!!!
 

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Discussion Starter · #5 ·
AH crud.
just ran a couple errands with my son, and it may even be worse now. I guess the next step is blocking off the MCV.

Don't understand why it ran so nice earlier but is now running like garbage.

If the MCV doens't work, I'm going after the distributor
 

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Have you done the basic tune up on it of plugs, plug wires, fuel filter, and air filter? Your thermo sensor or idle compensator could also be bad. I know on my trooper when I accidentally unplugged the vaccume line that attaches to the idle compensator my trooper would run fine for close to my whole 12 mile daily trip to work then whenever I would slow down and push in the clutch to turn into the parking lot the idle while the clutch was in would be horrible and the engine would miss badly. It even got to the point where when I would push in the clutch to slow to turn the engine would shut down but it would fire right back up and run fine. I started checking plugs and wires and everything else until I started the engine with the hood up and herd a sucking noise and finally found that little vaccume hose and I hooked it up and it ran fine from then on. But it might be something entirely different.
 

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Discussion Starter · #7 ·
The fuel filter is brand new, the plugs are fairly new, the wires are in good shape. The problem continues however. I tried bypassing the MCV, that didn't have any effect on the problem. I also cleaned out the MCV as best I could. Even though the Pipe that goes between the intake and exhaust, I made sure that little flapper was working properly, cleaned it out, tested the vacuum on it, etc. I tried to adjust the carb, but could only find the idle adjustment screw. I couldn't find a mixture adjustment on it. I thought maybe it had just been leaned out. I have a few more questions.

1. What's the best way to bypass the EGR to see if that is the issue?
2. If my temp sender wasn't working (which its not) would that cause any issues?

I drove in this morning and it ran GREAT for about 15 miles, then it it started it's stuff up again, though not as bad as when I was driving around yesterday. It still stumbled off the bottom and missed when cruising.

If I don't get this fixed, I'll have no choice but to go back to work on my transmisison on my Jimmy... :shock:
 

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Discussion Starter · #9 ·
I still need to pull the distributor...the previous owner says there's a screw in the back that is a nightmare to remove...so I'm procrastinating. I want to check the cap and rotor to make sure all is well.

I'll put that on my list for tonight.
 

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If my temp sender wasn't working (which its not) would that cause any issues?

Is your heater working? Meaning is it blowing hot air?

I thought my sending unit was bad and it was a partially stuck thermostat.

That would account for some of your symptoms, if you were not getting to normal operating temps.

Joe
 

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Discussion Starter · #12 ·
a friend of mine has a temp gauge I can borrow, he said to open the radiator cap as soon as I get home (carefully mind you... :shock: ) and see what the temp is. Either way, if it's around 180, I probably have a stuck thermostat.

Will there be any benefit to me running a 160 thermostat? Keep in mind in Central FL where it was like 80 degrees on New years day.
 

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Discussion Starter · #13 ·
well, we ran out at lunch at tried it. Temp at radiator cap never went over 115.

He was able to poke the EGR open which about killed the engine, but googling tells me problems with the EGR could cause these symptoms.

I'm going to try to pull the codes tonight, I guess you can Macgyver together a jumper and count the flashes to get yoru codes. Maybe it will tell me something.

With a new EGR going about 65 bucks, if that turns out to be the issue, I'll fab a blocking plate and get rid of it.
 

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4x4Dreamer said:
He was able to poke the EGR open which about killed the engine, but googling tells me problems with the EGR could cause these symptoms.
Sounds like the EGR is doing what it is supposed to be doing. EGR should only open when the engine is cold for a certain RPM range. Otherwise it should be closed. If the truck was idling really rough when warm then I would suspect the EGR of being stuck open.

With a bad temp sensor or stuck t'stat so that it never gets to proper temp it could be opening the EGR when it shouldnt be, but thats not the EGR's fault and the problem lies elsewhere.
 

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Gizmo42 said:
[Sounds like the EGR is doing what it is supposed to be doing. EGR should only open when the engine is cold for a certain RPM range. Otherwise it should be closed.
The EGR is there to reduce combustion temperatures when under load not at idle. One not closing at idle can cause stumbling problems.
 

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Discussion Starter · #16 ·
I'm wondering if the EGR is doing just that. Today, it ran great on the way to work ( I have about a 35 mile drive to work ). The last 2 or 3 it started stuttering at certain rev ranges. My heater still isn't blowing all that great, but I don't care about that other than it's a possible symptom. My temp gauge is registering now, though it has never pulled the needle above the C. Either way, yesterday when the Previous owner and I were poking around, he opened up the EGR manually a few times, and it's run much better since. I think I may just pull the EGR off and give it a good cleaning, then put a new gasket on it. I'll probably throw on a new cap and rotor while I'm at it. The P.O. doesn't remember if he replaced the thermostat or just nixed it all together. So that's in my near future as well.

This is quite a mystery.
 

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Discussion Starter · #17 ·
On second thought, I'll be making a blanking plate to get rid of the EGR. I'll be happy to post pics if anyone wishes.
 

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Before you do anything else replace the thermostat with the recommended 180 degree model. Make sure you put the bleeder hole in the thermostat in the 12 oclock position.

Then report back.

Joe
 

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Discussion Starter · #19 ·
Today I pulled the distributor cap (made in Italy) and rotor, they were both in pretty sad shape. I put a new rotor and cap (made in Japan) and fired it up. Runs lke new again. Idles smoother, pulls from down low and seems happier in general. I'm giving it the "problem fixed" stamp.

Thanks for your help everyone.
 
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