1990 isuzu trooper doesn't crank (no power to starter)

bamashooter Offline

Wheeler

I'm wondering if the "kill" and remaining dead situation is related to the circuitry of the roll over shuts off power to the fuel pump deal?

Re: 1990 isuzu trooper doesn't crank (no power to starter) [Re: bamashooter] #1005070 08/23/10 12:54 AM

Joined: Sep 2008

Posts: 28

Getting the Wheeling Fever

Hi,

The rollover switch is an idea. Where would the rollover switch come into the fuel pump circuit??? When the ignition switch is in the start position I have power to the fuel pump. If the rollover switch was cutting the power to the fuel pump would the fuel pump get power when the ignition switch was in the start position??? It looks like there are 3 connections between the fuel pump relay and the fuel pump itself. If there was a break in any of the connections the fuel pump wouldn't get power when the ignition switch was in the start position.

It looks like the fuel pump relay, the engine relay, the clutch switch and the a/c blower relay are all connected to "G100" as a ground. The engine relay goes through "S105" to get to "G100". The fuel pump relay also goes through "S105" to get to "G100". The clutch safety switch goes through "S207" to get to "G100". Would you have a diagram for "G100" , "S105" and "S207" ???? It seems like everything seems to be connected together in some way. It looks like the "panel lights" are connected to the engine relay.

The only thing else that I can see that is connected to the fuel pump circuit are the fuel pump relay diodes which are connected to the "instrument panel" lights.

Thanks for the help.

Mike

Re: 1990 isuzu trooper doesn't crank (no power to starter) [Re: fremont] #1005071 08/23/10 05:11 AM

Joined: Apr 2008

Posts: 135

bamashooter Offline

Wheeler

The fuel pump has dual circuits. One circuit activates the pump during start mode. Upon start and running, the task is transferred over to the alternator. Unlike many vehicles, the pump does not power up if the key is only turned to the on/run position. Let me know if the fuel pump circuit isn't in those illustrations so I can upload them to you. The following was easier to copy from http://forum.planetisuzoo.com/ than to type it myself.

There are 2 fuel pump circuits. Main one keys from the alternator after the engine is running. The other one bypasses the main one when the starter is turned to pressurize the fuel system until the engine is running and the alternator is putting out voltage. If they are checking in the start mode they are missing the big picture. This stuff never fails the test in start mode unless the fuel pump is bad. The engine kicks and sorta starts then dies shortly after you let go of the starter because the alternator is not taking over. The test is simple. You need to remove the fuel pump relay and jumper 2 terminals that will send juice from a constant hot to the fuel pump. If the truck runs it is the alternator! Easy test. It has been written up many times with a picture that shows you how to jumper it. Search for the one of the posts and do the test. If it then doesn't work you can move on to looking for other problems. Alternators do not like to get wet. Do the easy tests for common problems 1st and go from there. 9 out of 10 times it is a common failure. There are 2 fuel pump circuits. Main one keys from the alternator after the engine is running. The other one bypasses the main one when the starter is turned to pressurize the fuel system until the engine is running and the alternator is putting out voltage. If they are checking in the start mode they are missing the big picture. This stuff never fails the test in start mode unless the fuel pump is bad. The engine kicks and sorta starts then dies shortly after you let go of the starter because the alternator is not taking over. The test is simple. You need to remove the fuel pump relay and jumper 2 terminals that will send juice from a constant hot to the fuel pump. If the truck runs it is the alternator! Easy test. It has been written up many times with a picture that shows you how to jumper it. Search for the one of the posts and do the test. If it then doesn't work you can move on to looking for other problems. Alternators do not like to get wet. Do the easy tests for common problems 1st and go from there. 9 out of 10 times it is a common failure.

Additionally, read this next thread and scroll down to the pic showing how to jump the fuel pump relay.

http://forum.planetisuzoo.com/viewtopic.php?t=13176

Re: 1990 isuzu trooper doesn't crank (no power to starter) [Re: bamashooter] #1005072 08/23/10 02:30 PM

Joined: Sep 2008

Posts: 28

Getting the Wheeling Fever

Hi,

Would you believe jumping the fuel pump relay did cross my mind. I have read about these alternators in troopers. They can charge the battery fine but be bad. The alternator turns off the panel lights. If jumping the fuel pump relay lets the trooper run is there anything else in that circuit besides the alternator that would cause this problem??? From what I have heard you can't put an aftermarket alternator in these troopers because of this circuit. The alternator has to be from isuzu. I'll let you know what I find out. Thanks again for all the help finding the short with the starter and engine relays. The diagrams were a great help.

Mike

Re: 1990 isuzu trooper doesn't crank (no power to starter) [Re: fremont] #1005073 08/23/10 05:35 PM

Joined: Apr 2008

Posts: 135

bamashooter Offline

Wheeler

It's my understanding that Bosch and NAPA Gold alternators work well. It's my understanding that jumping the relay is a way to determine if the alternator is failing to perform that particular task.

Last edited by bamashooter; 08/23/10 05:37 PM.

Re: 1990 isuzu trooper doesn't crank (no power to starter) [Re: bamashooter] #1005074 08/29/10 05:53 AM

Joined: Sep 2008

Posts: 28

Getting the Wheeling Fever

Hi,

When I jumped the relays the trooper still wouldn't start. The fuel pump was running with no problems. I decided to check one more thing. I checked the "mechanical" engine timing. It was almost 3 teeth off. It must have jumped when the trooper got on the main road and that is why the engine died and wouldn't start back up. I corrected the "mechanical" engine timing and the trooper will start now. It runs like crap though. I really don't trust it to be driven any distance right now.

In the process of adjusting the "mechanical" engine timing the distributor alignment got messed up. The "electrical" ignition timing is way off now. I am planning to re-align the distributor this week. I believe that I am leaking oil from around the distibutor o-ring. I have ordered the o-ring from the dealer. It should come in within a few days. I didn't want to pull the distributor out twice to correct the problem. I'm hoping the "mechanical" engine timing holds this time. I am hoping to get at least 30,000 miles out of the new timing belt. It has been jumping out of adjustment every couple of months for the last year and a half. That is why the trooper was down for repairs in the first place. When I first changed out the cylinder head 4 years ago after it cracked the trooper ran great for 30,000 miles. That is when the "mechanical" timing started going out. I wonder if the electrical issues that I was having with the trooper were causing the "mechaincal" timing to jump.

Thanks again for all your help in troubleshooting the electrical problem that I had with the trooper. The wiring diagrams really helped to find the problem. I really appreciate the help. You have been great.

Mike

Re: 1990 isuzu trooper doesn't crank (no power to starter) [Re: fremont] #1005075 08/29/10 11:33 PM

Joined: Apr 2008

Posts: 135

bamashooter Offline

Wheeler

Quote

Causes for a jumped timing belt vary. Degraded belt, improper belt installation oil pump, camshaft, oil leakage onto belt, timing belt tensioner, etc. Jumping 3 teeth and shutting down the way it did; I'd be concerned about some bent / bad valves also. To me, it's imperative to pull the head (replace head gasket), check valves, replace belt, check the tensioner and replace if questionable. Rereading this thread, assuming all related pulleys are aligned and torqued correctly, I'd say the tensioner should be replaced. It's the only part I can think of which would allow for a jumped belt "now and then".

Re: 1990 isuzu trooper doesn't crank (no power to starter) [Re: bamashooter] #1005076 09/09/10 09:44 PM

Joined: Sep 2008

Posts: 28

Getting the Wheeling Fever

Hi,

Yeah the timing belt tensioner was replaced during a prior timing belt change almost a year ago. I checked the engine compression a couple of days ago and it was 135 PSI on all cylinders. I reset the distributor and changed the o-ring when I had the distributor out. I started it up and it ran good. I went to set the ignition timing because it was advanced off the scale. I was able to set the "ignition" timing to 12 degrees BTDC. The trooper was running good for a brief time. I had it running for about 10 minutes before going to take it on a test run. The trooper started running bad just as I was going to take it out on the road. The trooper was idling around 500 RPM. Prior to resetting the distributor I was having trouble geting the "ignition" timing set. Would the distributor assembly itself cause the "mechanical" timing to jump a tooth over time???? Would the electrical problems that I was having effect the distributor assembly itself??? Thanks.

Mike

Re: 1990 isuzu trooper doesn't crank (no power to starter) [Re: fremont] #1005077 09/15/10 12:36 AM

Joined: Apr 2008

Posts: 135

bamashooter Offline

Wheeler

Sorry for the late reply; didn't see your current question. I'm sure the internals of the dizzy can be negatively impacted by changes in voltage. That one's beyond me as to troubleshooting. I don't see the ignition timing impacting timing belt position unless you had such a serious backfire or more that it physically knocked the hell out of the valvetain causing the belt to jump. Doubtful. Hopefully, one of the guys with a lot of mechanical skills will chime in. Once again, if you don't get responses, post this question over at http://forum.planetisuzoo.com/. We're all here to help one another, regardless of forum.

Re: 1990 isuzu trooper doesn't crank (no power to starter) [Re: bamashooter] #1005078 09/15/10 01:04 PM

Joined: Sep 2008

Posts: 28