That was what I was thinking, a vacuum leak would just lean it out too much, and most likely burn something up in the engine, not outside the engine. I just don't know how to diagnose it, if it is bad injectors. I wonder if some place could, or would test them, if I took them individual injectors? I don't want to just throw parts at it until it is fixed, but I really don't have any way to diagnose this without a CE code or some other clue. Do you suppose that it could be a regulator problem? If the regulator is bad, could too much fuel pressure cause this? I wish there was a schrader valve on the fuel rail, so I could check the pressure. I will just have to pull the lines and dead head them to see what the pressure is. I will pull codes again, but it hasn't even blinked the CE light. It's got me baffled. <img src="/forums/images/graemlins/scared.gif" alt="" />

Sounds like you've checked the timing system, which is what I would have looked at first, especially since the 'flat' feeling you described seems to have happened after you installed the used dizzy...

Did the plugs read OK? Google for "plug chop" if you don't know what I mean.

A compression test would help eliminate burned valve(s) and would be my next suggestion.

You could unbolt and bungy-up the exhaust to rule out a plugged cat. I can't recommend chopping the cat even if it is plugged -- most modern vehicles (arguably the Trooper is such) run poorly without a cat. FYI and FWIW the smaller aftermarket cats sometime work jsut as well/better than the OEM cat.

FWIW, the O2 sensor may be fine -- they like high temperatures, but are picky about contaminants.

Injectors can fail closed (in which case you'd be lean, and not lighting up the exhaust manifold) or have a crummy spray pattern (also more likely to lean, unless you're pooling fuel into the chamber), but they don't fail open.

Mist carb cleaner or propane around your intake from the filter on back to the head... a buddy of mine had an intermittent failure based on a gap in the accordion hose in the intake. It only spread far enough to leak air when the engine torqued over and spread the gap open... a real bugger to troubleshoot! But then again, not something that would make the exhaust manifold glow.

It is tough to troubleshoot on the internet, but it sounds like you are working your way through fuel, fire, and air, which are the key elements to internal combustion. Besides checking compression, I don't have any real suggestions. <img src="/forums/images/graemlins/frown.gif" alt="" />

Randii

Well, here are the results of the compression test. #1 - 120, #2 - 120, #3 - 105, #4 - 120. Not the best in the world. The #3 plug looks like it is more rich than the other three. However, I don't think I have burned valves. I say this, because all the valves are still within spec on the lash adjustment. I think a burned valve would be tight, and not still within adjustment (adjusted the valves about 10K ago). So I have weak compression, a rig with an unexplained fuel problem, and almost 313k on the odo. It might be time to throw in the towel. I am just not sure it is worth spending the money to fix the problems. I have found an entire intake assembly(throttle body to the head, with injectors) for $200 and for another $75, they will throw in the computer. I am not so sure that my rig is worth spending another $275 on it. Frankly, three years ago, I only paid $175 for it in the first place. I put a head gasket and tires on it, and the rest is 100k of history and good times. It really owes me nothing. I think I might just take off my new tires and pull my radio and battery, and call the scrap yard. It was a good run, but it might be over. But I have to say, even with a second engine at 180k, due to a head gakset failure, 313k is a testament to the durability of the little Isuzu. <img src="/forums/images/graemlins/cheers.gif" alt="" />

A single burned valve, if that is what is causing the lower # on #3, won't make the manifold glow.

I still think you have a timing issue. You say the mark is dead on, but...to make sure, you need to pull the front timing belt cover and look at the key on the crank and or see if the sprocket lines up on the indexing mark. Then, install the ballancer and see where the timing mark is. Double check the cam is lined up and that the dizzy is lined up with the cam. (This involves pulling the valve cover.) You got to make sure the base/mechanical timing is set before anything else. There is no way to really do it by "feel" and expect to get it right.

Why a timing issue? It seems like it is way retarded(yeah, bad pun), with a loss of power down low and it running strong at higher RPMS.

Also, how did they test the back pressure? To do it properly, it does take a bit of time, but someting like a clogged cat or a shifted core in the muffler could explain the symptoms too.

I would not give up quite yet as I don't think it is a drastic as it seems. Athough, you could have a valve problem that is due to the timing or exhaust restriction issue.

Michael

I pulled the covers and did physically check all the marks. I did that this morning, while I was trying to diagnose this problem. I agree that it does seem like timing, but I have checked all the marks tried two different distributors, replaced cap, rotor, plugs and wires.

The muffler shop cut a hole in the pipe, ahead of the cat, and clamped on a pressure transducer, it barely got over 1 psi. I removed the front cover, and the valve cover, and checked everything this morning. As far as I can tell, the mechanical portion of the timing is fine. With it running better in the higher rpm range, it doesn't seem like a coil problem or anything of that nature.

It really does act like timing, but I have checked that whole system. I ohmed the coil, according to the procedure in the Haynes manual, and it checks out okay. The plugs all looked a little rich, not the light tan they should be, but a little darker. Not dark brown, but not light tan. #3 looked the most rich, but like I said, I checked all the valves, and they are still in adjustment. I would think a burned valve would be tight. It seems like it is just getting totally bombarded with fuel in the lower rpm range.

My mileage is only in the mid teens, down from the 20-21 I usually get. It just seems really odd, that this started after the alternator change. I am wondering if during my trouble shooting on the alternator, I did something to damage the ECM.

This did not come on gradually, it just happened. The only other thing I changed at the time, was the fuel filter. The old filter was terribly filthy, after only one year (roughly 25k miles). I really don't want to give up, but I don't know where to turn next.

I did not pull the lower cover and the crank pulleys. Do you suppose it has slipped on the crank? Isn't it the outer ring that usually slips? I replaced the damper and pulleys about a year and a half ago, and when I did this I scratched a mark in the other pulleys, that bolt to the front of the damper, and that mark has not moved relative to the timing mark on the damper pulley. The bolt in the front had actually come loose at that time, but is still exceptionally tight now (tightened with a very larger cheater and held with a generous amount of thread locker). T

he keyway in the old damper was about a half inch wide. There was no visible damage to the crank, only to the damper and the woodruff key. Apparently the crank is much harder than the pulley and the key, or I just got really lucky. I am fairly certain that the pulley has not slipped.

I found TDC with a screwdriver in a spark plug hole, and could physically feel the piston break over at the top, almost exactly on the zero degree mark on the crank. With the upper cover off, the timing marks on the upper pulley lined up exactly with the mark on the aluminum portion of the timing cover, and the timing mark on the crank was right on zero degrees. I am confident the mechanical timing is right where it should be. Is there anything besides timing that could cause these problems?

The muffler is only a few months old, I am fairly certain it is okay, it isn't even rusted yet. Maybe the exhaust is plugged farther up?? It acts like timing, but I can't find anything wrong with the timing, so it has to be fuel, but how?? I am open to any suggestions, but I really don't know what to check next???

EDIT BY MOD: Uber-paragraph broken up for ease of readability...

Couple of things:

First, look at the bright side: Glowing red manifolds make great cigarette lighters.

Second, Everyone is acting like it just has to be ignition timing(and I agree), but it could possibly be _injector_ timing. While I am not sure about Isuzu engines of this vintage, some engine's ECM use cranshaft position AND distributor information for injection timing. Discharging fuel just a few degrees late would send a lot of unburnt fuel out a partially open exhaust valve. COuld all of the distributor modules you have tried with these distributors be different enough fool your ECM??

Just throwing it out there for discussion since I don't know this particular engine well enough to know if this guess is even valid.

NCDiesel

Were I smoker, that is great solace, maybe cigars <img src="/forums/images/graemlins/shiner.gif" alt="" />! I don't know if that is possible or not, I don't know if there are differences between years on the computers or distributors. I know that the only position comes from the distributor. I do not know of a crank position sensor, or any other sensor that reads the position of the engine, besides the optical encoder in the distributor. Is there a difference between distributors of different years on the 4ZE1?? Maybe a reset on the computer? I can get the computer from the Trooper of the current distributor, for $75, at the salvage yard. I don't think there would be a differnce, but I really don't know. EFI was still relatively new when the Troopers got theirs, maybe there was some developmental stuff early on, and things did change. I think both of the distributors I got, came from newer models. I am thinking that I will just advance the timing a long ways and see what happens. I really don't know what else to do.

Okay, so I advanced the timing, probably beyond 20 degrees. I went to where I could hear it knock when I revved and then back off just a little. I got back some of the snap off the bottom, but it is still lighting up the manifold. I took it for a quick drive, only about five miles and it got hot enough to be dull red, in that short amount of time. The road to my house is pretty steep, nearly a mile of 12% plus grade, but even on that it should not get hot enough to light up the manifold. I intentionally drove it in the 2000-3000 range just to see if it ran better. The surging was for the most part gone, but the manifold is still getting hot enough to glow. I am going to take it to another muffler shop and see what they say about the back pressure. This really is not making sense. The timing change helping, tells me it must be a timing issue somewhere, but I don't know where. I suppose the next step will be the removal of the crank pulley/damper, to physically verify that the pulley has not slipped. I am confident that it has not, but I don't know what else to do. I think somehow, it is getting fuel at the wrong time, and it is getting burned in the exhaust. Maybe I do need injectors?? Could the throttle position sensor in any way contribute to this?? Maybe I will get the salvage yard parts and see what happens. I hate to spend the money if it won't fix it, but it would probably be cheaper than taking it to a mechanic. Could a bad O2 make it do this? Maybe I should try to replace it and see what happens.

FWIW, a burnt valve doesn't necessarily go off-spec on lash... but I agree with Michael that one burnt/blown valve won't light up your manifold. It would explain why your #3 plug looks wet/rich. That the others look rich, but it runs crap low but smooth high makes me think the distributor advance isn't working well. That's a pisser since that's all computer-controlled... but the fuel pressure regulator *is* vacuum-controlled, have you checked fuel pressure? I could see that mimicking badly-retarded timing (no power low, but smooths out high). Good thinking, NCDiesel, but for the 4ZE1, crank position reads off the dizzy, with an optical shutter. Not sure how that could slip?

JF, you're definitely high-mileage, but IMHO, no sense walking away until you KNOW what's up.

Randii

The dizzy could not slip unless the pin in the gear/shaft were to shear. The end of the shaft where the encoder ring attaches, has a flat on it , and the ring is located by two tabs and the flat. You cannot even put it on upside down. I had suspected that maybe oil had gotten inside the distributor and was gumming up the sender or the ring. There was some oil, but none of the slots in the ring were plugged. I cleaned it all out and reassembled before my test drive tonight. If I set the timing where it should be, it is sluggish, if I advance it, it loses some of the sluggishness, but the red hot manifold is still present. Is there any way to test the function of the ECM? Can a dealer or mechanic plug it in and do some tests. Maybe the combination of age and the alternator dying did something to the computer. Perhaps seeing marginal voltage for a time, or maybe the rebuilt alternator did something to it. Maybe even running it without the engine relay in place did something. I really don't know. All I know is that I have a red hot manifold and I have no idea how to fix it. It seems like timing, but I have eliminated most of those factors. It is pointing to computer or injectors. <img src="/forums/images/graemlins/confused.gif" alt="" /> I really don't want to walk away, but just throwing parts at it to try to fix it pushes it past the point of diminishing returns. If I could find the problem, it would be easier to determine if it is worth repairing. It is rusty, but the tranny shifts fine, the four wheel drive works, the AC even works. I have it charged with a hydrocarbon refrigerant, but it works like a champ. The rear brakes howl like seals in heat, but they still work well. It doesn't even wear tires poorly. I got over 50k out of my last set of 40k tires. There are more reasons to keep it, than to get rid of it, but I can't drive around with a glowing manifold, it is just not safe.

Thanks. I was thinking along the lines of the signal from the distributor being different, not really a slip in the module/sensor in the distributor.

In other words, the ECM is getting told one thing about engine speed, but because the dizzy module is slightly different than what came with the vehicle, engine speed is really something else and timing is off because of it.

Again, not sure if this makes sense for this particular engine.

NCDiesel