So my '88 Trooper has decided that it does not want to run for extended periods of time. I am not sure if it is acting like a fuel problem, or an ignition issue. I will be happily cruising down the road, and it is just like the fuel was turned off, or the spark was turned off. When I try to restart, it starts and dies, like it has a massive vacuum leak or runs out of fuel. If I hold the pedal to the floor, I can sometimes get it to run, but it will only maintain about 3000-3500 rpm even with it floored. I can keep it running a little longer if I pump the pedal frantically, but not for more than a few seconds. If I can get it to hold above 3k for more than a few seconds, it will stay running, but as soon as it drops below 3k it dies again. While I am doing this, and trying to keep it above 3000, the O2, battery, and fuel light all stay on, but the CE light does not stay illuminated. If I can get it to stay above 3k long enough I hear a relay behind the dash click, and the lights go off, but it will not always stay running. After about 10-15 minutes, it will start and drive another 15 miles or so. I checked codes, and nothing is stored. The fuel pump is barely over a year old, and the filter was replaced at that time. I don't know what the relay is that is clicking, but once it clicks, it will usually stay running. Not always, but usually will stay running. While it is sputtering and coughing, the alternator also does not kick in, but as soon as that relay clicks, my volt meter jumps right up to 15 volts or so. I am going to replace the fuel filter, just because, but I don't think it is the problem. If anyone has had a similar problem, please let me know how you solved it.

I am going to guess that you have an alternator going South. Without the alternator putting out enough, the system is designed to shut down the fuel pump, via a relay.

The reasoning is that if there is an accident that results in the engine stopping, you don't want the fuel pump to continue to add fuel to the fire, so to speak.

I would take your alternator in to have it checked.

Well, here's a shot in the dark. I did have the same problem and it went on for months, the fix is free, so give it a look.

YOUR FUSE BOX = Look inside of it [take off the plastic clear cover]and check the inchworm looking wires. Are they plugged in tight? Pull them out and put them back in tight.
And make sure that the clear plastic cover to the fuse box is not and does not bump these wires loose when it is replaced.

I spent lots of shop time, towing and hours and then one day
just messed around and found the wires were loose. Haven't a problem one since then.

2.6?
I've got the same probaly, or at least it sounds that way.
does it only happen when its hot?
If I give it some gas, it'll run, but if I coast, it will stall. No fuel, then I crank, and crank and crank, then it'll refire and run all day.

Jim, I think you hit the nail on the head! I just spent a few hours in the garage swearing, err I mean working on the Trooper and I also think it is the alternator! After messing with a few things and changing the fuel filter, I went to pull it out of the garage and when I started it, the relay under the dash was clicking like crazy and no juice besides the 12 volts from the battery. When I rev it, it must just get the alternator excited enough to generate enough juice to make it charge. Probably a regulator problem, but since it is internally regulated, a new alternator is in order. Once the rpms drop, no more charge and the fuel pump kicks out. I guess I will track down a new alternator tomorrow. The little green wire also looks fine. I am surprized that the 12 volts from the battery will not sustain it longer. Kind of weird how Isuzu uses so many relays. I guess if they don't have the juice to hold them shut, they just click open and no more fuel. It really should come as no surprise that the alternator is dying, it has 312,000 miles, and I think it is the original!! I know it has not been replaced in at least the last 200k. Anything to look out for buying an alternator besides not buying one from autozone or checker?? Also, it happens cold or hot, and yes it is a 2.6.

I had to replace my alternator roughly 5 months ago. I went to a local automotive supply shop "smother's electric," and I was able to buy a brand new alternator 60amp, for about $150.00. It's been running like a champ ever since. They aren't cheap (these alternators) but they seem to last for quite awhile.

- Jim

so the alternator is fine, what next?? I am about ready to just push this thing out into the road and light it on fire! I have swapped all the relays, thinking it might be one of them, but no luck, nothing changes. It still starts and dies, unless I can get the rpms over 3500 or so, and then it will kick in, but as soon as the key is cycled I am right back where I started. I have had fuel pumps die before, and the idiot lights do not stay on when a pump dies, the car just quits running! This is definitely in the charging system somewhere. I guess I will start chasing wires and see what I can find. So a couple more questions... What color is the main relay?? Is it located behind the VSV?? None of the wire colors on any of the relays behind the VSV correspond to the diagram I have. Where is the main fuel pump relay?? I know of the one in the fuse box, but the diagram shows a second relay, and I don't know where this one is hiding. I have swapped all the other relays, to no avail. It still just starts and dies, starts and dies. Now I cannot even get it to stay running at all! Just starts and dies. I suppose I will have to consider the fuel pump next, but it doesn't make sense that it would be dead so soon, it is barely over a year old. I even replaced it with a pump from a reputable parts store, not junk from Checker or Autozone. I don't understand why the three lights (O2, battery, and fuel) stay on?? It is clear the alternator is not kicking in, but I have no idea why. It is late and I am frustrated! I will just light the thing on fire tomorrow and enjoy the funeral pyre! I wish I had a video camera, and I would tape it burning. Maybe I could sell the video on the internet and get enough money for a new rig.

The dying is no longer random, it now just starts and dies. I cannot even get it over 2500 rpm, it runs out of fuel before that can happen. I have tried a different alternator, and no change. I will have to get the new alternator tested, but it seems really strange that a brand new alternator from Napa would be bad too. What relays could affect this thing this way?? I have swapped all the relays I have spares for (engine, starter, fuel pump), and I don't know where to go from here. Where is the second fuel pump relay?? Where is the main relay. My wiring diagram shows it behind the vsv, but there are four relays back there, and none of them have the color wires shown in the diagram for the main relay. For that matter, not many of my wires are the same color as what the wiring diagram indicates. I am at my wits end here. I really don't want to take it to a mechanic (frankly, I don't think they could find this any better than I can) since they would just take my money and probably not be able to fix it. The fuel pump is not that old, and besides that, if it were the fuel pump, the idiot lights would go off when it started, even if it did quit again. The O2, battery, and fuel light are all staying illuminated, it acts like the alternator is not charging, but I am pretty sure the new alternator is good. I am totally stumped.

Maybe your problem isn't the charging side. Maybe it's the ground. I've had a few electrical problems that tested fine to the battery ground but zero to the frame. Corrosion is a great insulator. Did you switch out the alternator relay? That's the one that switches the circuit from crank mode to run mode. Blue cube in the relay box on mine. If that's kaput you won't get fuel. Maybe the fuse sockets are corroded. Pull them out and plug again.

As old as it is you have to assume all those years of rattling down the road might have loosened something. I recently had a problem with headlights that wouldn't come on. Relay just wouldn't pull in. After many hours of banging my head in the engine compartment I found the real problem was under the dash in the connector block that connects the interior wiring harness's to the exterior ones. Some electrical contact cleaner and plugging it in and out a few times solved it. Maybe the ignition switch connector is your problem. The relays work on such tiny amp levels that even a little resistance from corrosion or looseness is enough to stop it from working.

I actually went through all the relays and the fuses I could get to with some some contact cleaner. As well as checking and cleaning all the fuseable links. I checked the grounds from engine to chassis and engine to body and everything looks good. It looks like tonight will be more cleaning and checking. I'll re-check all the firewall connectors. Maybe that bulkhead connector could be the problem. I am sure that the years of salt and vibration have taken a toll. I just need a couple more years out of it, and I can buy a newer rig. I might shoot for something mid '90's, now that would be living high <img src="/forums/images/graemlins/notooth.gif" alt="" />! I just hate electrical gremlins like this! They are so hard to track down. How different do you suppose the pin outs are on the engine relay vs. the fuel pump relay? Same pin pattern, but I am sure there is different function.