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#620791 - 06/30/05 04:18 AM Won't stay running  
Anonymous
Unregistered

I have a 91 Montero that we just had the ECU gone through and repaired and the repair facility is telling us to remove the idle speed motor of the idle speed control but we want to make sure that after that item is taken out is there any other part involved to make sure there is nothing else from that sending information to the computer. The guy told us that we could just manually adjust the idle and not reinstall a new ISC. Any thoughts, help, suggestions would be greatly appreciated.

Last edited by redduck; 07/02/05 02:28 AM.


#620792 - 06/30/05 11:50 AM Re: ISC removal?  
lochabay  Offline
Wheeler
Joined: Oct 2004
Posts: 125
I would get my car out of there pronto.


#620793 - 06/30/05 12:11 PM Re: ISC removal?  
FrankR  Offline
Web Wheeler
Joined: Feb 2004
Posts: 10,238
Columbia, SC ****
That sounds like p*ss poor advice to me - others may disagree, but the system was designed to utilize the stepper motor. My concern would be that disconnecting the stepper motor might cause the ECU to go into open loop mode and your fuel mileage would suffer. I'm not sure it would cause that, but in any event the problem could still be in the ECU and not in the stepper motor. With advance apologies for the length of the post, here's how to find out where the problem lies:

Check ISC Operation Sound

1) Listen while you turn on the ignition. You should be able to hear the stepper motor kick in as you turn the ignition switch to "ON" (without starting the engine).

2) If you don't hear the operation sound, check the stepper motor circuit (if the circuit is normal, the problem is probably the in the stepper motor operation or the ECU).

Check Coil Resistance

1) Disconnect the connector. Note 6 pins (2 rows of 3 pins) on the ISC - they are numbered 1-2-3 (top row, left to right), 4-5-6 (bottom row, left to right).

2) Measure resistance between terminal 2 and terminal 1 or terminal 3. At 70 degrees you should read 28-33 ohms.

3) Measure resistance between terminal 5 and terminal 6 or terminal 4. At 70 degrees you should read 28-33 ohms.

Check ISC Operation

1) Remove the throttle body.

2) Remove the stepper motor.

3) Connect the positive (+) terminal of a 6vdc lantern battery to terminals 2 AND 5 of the connector.

4) Hold the stepper motor in your hand so that a finger or thumb is on the tip. Connect the negative (-) terminal of the battery to each terminal in the sequence described below, and check whether or not there is tip vibration as a result of stepper motor activation.
a) negative to terminal 3 and terminal 6
b) negative to terminal 1 and terminal 6
c) negative to terminal 1 and terminal 4
d) negative to terminal 3 and terminal 4
e) negative to terminal 3 and terminal 6
Repeat the test in the reverse (e-a) sequence.

6) If you feel vibration in all combinations, the stepper motor is normal.

If the stepper motor passes the tests, I think I'd have another conversation with the fellow who repaired the ECU.

Good luck,
Frank


'89 [color:"white"]G-Raider[color:"white"] [color:"black"]Supercharged 3.0L, MegaSquirt 2, lockup A/T, 2.5" exhaust, 172k, Cibie H4s/Oscar SCs, Hella Micro DE fogs, Cobra CB, Superwinch hubs, LSD rear/Aussie Locker front, Bilsteins, Lifeline AGM, Rust-Oleum

#620794 - 06/30/05 01:13 PM Re: ISC removal?  
Anonymous
Unregistered

Did you get your ECU repaired by AVPRO?? I had the same problem with mine (ISC blowing some parts in the ECU) and sent it to them. I forget the name of the person I talked to, but he also recommended that I simply unplug the ISC. After looking at the price for a new one, I went ahead and tried it. I had to adjust the pintle of the ISC a few times until the truck idled at 800ish RPM. That was approximately 6K miles ago. The ECU adjusts the idle up or down as necessary. Turning on the AC with the truck idling in gear does drop RPM slightly, but it is not a problem at all. I am getting around 15 MPG, which may be a little low??? I have had no ill effects from this at all (hot weather or very cold here). So if you want to, give it a shot. My truck is a 1990, but I do not think there are huge differences in the ISC/ECU among years. Good Luck <img src="/forums/images/graemlins/wink.gif" alt="" />


#620795 - 06/30/05 01:31 PM Re: ISC removal?  
Anonymous
Unregistered

I did get it done by avpro just unsure if just removing the isc is all I have to do, is there another part involved like a sensor?


#620796 - 06/30/05 02:03 PM Re: ISC removal?  
Anonymous
Unregistered

Here is what you need to do:

1) Unplug the electrical connector to the ISC
2) Start the truck and check the idle speed.
3) If the idle is too high or too low (should be 700-800), remove the ISC (3 screws) then turn the pintle of the ISC either in or out to adjust the idle.
4) Reinstall the ISC, leaving the electrical connection unplugged.
5) Repeat this process until you get the idle in the acceptable range.

You also may want to clean the ISC and throttle body. This will help with idling. I know this is a hokey fix, but it has worked just fine for me.


#620797 - 06/30/05 02:22 PM Re: ISC removal?  
Winston  Offline
Rock Warrior
Joined: Feb 2005
Posts: 509
SF Bay Area
ISC/IAC Data and Repair Links

Here is a good page about the ISC along with some links of places that will repair it for you. They only charge $90. If that is in your budget I think it is worth having it function properly.

As far as removing the IAC; I do not think they meant to remove it, you should just unplug it and then adjust it manually as noted in a previous post.


'90 Montero XLS (Sold, sadly)
'95 Montero LS 160k
'03 Montero Limited 30k

#620798 - 06/30/05 02:54 PM Re: ISC removal?  
FrankR  Offline
Web Wheeler
Joined: Feb 2004
Posts: 10,238
Columbia, SC ****
Quote
...is there another part involved like a sensor?


Yes, possibly. There is a Throttle Position Sensor and an Idle Position Switch plus a Fixed SAS adjustment procedure.

However, if you intend to disconnect the ISC, there's no need to do any further diagnosis. If you want to find the problem and try to fix it, begin with a check of the ISC.

Good luck,
Frank


'89 [color:"white"]G-Raider[color:"white"] [color:"black"]Supercharged 3.0L, MegaSquirt 2, lockup A/T, 2.5" exhaust, 172k, Cibie H4s/Oscar SCs, Hella Micro DE fogs, Cobra CB, Superwinch hubs, LSD rear/Aussie Locker front, Bilsteins, Lifeline AGM, Rust-Oleum

#620799 - 07/02/05 12:51 AM Re: Won't stay running [Re: FrankR]  
Anonymous
Unregistered

I have tested the ISC and any thing that has to do with terminal 3 wont work. I also tried to disconnect the ISC as advised and still have the original problem. It will start, run for about 10-15 seconds and then die. It will start immediatly and just keep doing this. It still has the same 42 fault code as before the computer was fixed. 91 Monty 3.0. Any help would be great. <img src="/forums/images/graemlins/angry.gif" alt="" />

Last edited by redduck; 07/02/05 02:11 AM.

#620800 - 07/02/05 02:26 AM Re: ISC removal?  
FrankR  Offline
Web Wheeler
Joined: Feb 2004
Posts: 10,238
Columbia, SC ****
Sounds like the ISC unit is bad. See if you can get one cheap at a junk yard and test it before you buy.

Let's cover a few other things and see if you can get it to run, though:

Will it run if you keep the rpms above idle after it starts? If not, when did you last change the fuel filter?

When did you last change the PCV valve? To test: Disconnect the PCV valve hose on the front of the intake manifold and apply vacuum - it should leak with vacuum applied. If not, replace the valve - it's tough to get to - buried under the upper intake plenum on the rear of the driver side valve cover.

When did you last replace the EGR valve? To test: remove the EGR valve, check for carbon deposits and clean if necessary. Apply vacuum of ~19.6 in.Hg and check for air tightness. Blow in air from one passage of the EGR and check for air passage at 11 in.Hg or more - at 2.8 in.Hg or less, air should not pass.

Check all around the engine for cracked or loose vacuum lines - particularly the purge control valve hose. The hose is attached to the round canister next to the coolant overflow bottle - runs to the purge control solenoid valve.

To test the the purge control solenoid valve - remove the connector and measure resistance - standard value is 36-44 ohms at 70 degrees. Disconnect the hose from the intake to the valve and blow in it - it should be closed when the engine is off and open when the engine is above 1500 rpms. Apply 12vdc to the terminals - should not hold vacuum.

Throttle position sensor (next to the ISC) - should read 3.5k-6.5K ohms at closed throttle.... should read 0.4-1.0vdc output voltage.

That should get you started - post back if we can help. Others may have some additional suggestions or short cuts.

Good luck,
Frank


'89 [color:"white"]G-Raider[color:"white"] [color:"black"]Supercharged 3.0L, MegaSquirt 2, lockup A/T, 2.5" exhaust, 172k, Cibie H4s/Oscar SCs, Hella Micro DE fogs, Cobra CB, Superwinch hubs, LSD rear/Aussie Locker front, Bilsteins, Lifeline AGM, Rust-Oleum

#620801 - 07/02/05 02:36 AM Re: ISC removal? [Re: FrankR]  
Anonymous
Unregistered

No it won't stay running if I use the throttle either. I replaced the fuel filter at the start of the trouble shoot. I have also checked the fuel system operation and done several other system checks. The TPS seems to be O.K. with 5.5 res. If I hold the contacts closed in the control relay it will run forever. I have tested the control relay and also tried another one the same results. Thank you for the input and would appreciate any help I can get.


#620802 - 07/02/05 03:05 AM Re: ISC removal?  
FrankR  Offline
Web Wheeler
Joined: Feb 2004
Posts: 10,238
Columbia, SC ****
That's weird - I guess you can add fuel pump and fuel pressure regulator to the list of suspects.

Do you know what ECU number you have? - Never mind - I see you have a '91. I have a good spare 6477 for an '89 I was going to suggest sending to you to swap in and see if it would run, but it's different from the '90s and '91s.

Check all of the wires and harness connectors around the distributor and coil - maybe spray inside the connectors with some electrical contact cleaner (RadioShack) just to make sure they're ok. Have you checked the coil resistance? Primary resistance should be 0.72-0.88 ohms. Secondary resistance should be 14.5K-19.5K ohms.

When were your wires replaced? Check the coil wire resistance?

Check the mounting bolts/nuts where the upper plenum attaches to the lower intake. Don't over-tighten in the aluminum, but snug 'em to 14 ft.lbs to make certain you don't have an air leak there.

Still thinkin' - this one's a head scratcher (as you've found out).

Frank


'89 [color:"white"]G-Raider[color:"white"] [color:"black"]Supercharged 3.0L, MegaSquirt 2, lockup A/T, 2.5" exhaust, 172k, Cibie H4s/Oscar SCs, Hella Micro DE fogs, Cobra CB, Superwinch hubs, LSD rear/Aussie Locker front, Bilsteins, Lifeline AGM, Rust-Oleum

#620803 - 07/02/05 04:21 AM Re: ISC removal? [Re: FrankR]  
Anonymous
Unregistered

I have checked the fuel pressure and fuel pump and tried another pump. I have done some checks of the ignition system and found the coil and related parts to be fine. This problem happened all at once. No previous warnings. I have been told to check the oil pressure switch and I replaced it. They range from $10 to $70 so I tried the $10 switch. This engine was rebuilt about 2000 miles ago so oil pressure should be OK to. I'm glad that someone else is challenged by this to. Thanks


#620804 - 07/02/05 05:12 AM Re: ISC removal?  
FrankR  Offline
Web Wheeler
Joined: Feb 2004
Posts: 10,238
Columbia, SC ****
You can try turning the pintle tip of the ISC to different positions as the other poster suggested worked for him, but I haven't tried that and can't suggest a method that would work other than what he posted.

You might try disconnecting the MAF sensor (in the air filter can) and see if it makes any difference.

Your distributor is different from mine and I can't help you with yours - Conner is familiar with it and perhaps he'll chime in here - hope so as his diagnostic skills are excellent.

If you have spark, fuel and air enough to start it, it seems possible that an electrical component is breaking down as current begins to flow. If that is happening, it's gonna be tough to figure out.

I assume it continues to run for a few seconds after you release the ignition key? If it doesn't and quits as soon as you release to the "Run" position, the ignition switch might be faulty. Otherwise, I wouldn't condemn the switch. How about hooking up your voltmeter to the battery side of the coil and see if you have voltage as the engine dies?

The power transistor (black thing next to the coil) is what triggers the coil - if you want to check it, let me know.

One thing you need to check is fuel pressure, but without a gauge and fitting it's tough because there's no test port. If you have or can borrow a gauge, you'll need a tee fitting. You'll have to release the fuel pressure, remove the hose fitting at the fuel rail and insert the fitting for the gauge between the fuel supply hose and the rail - otherwise you'll have to cut the hose, use a barbed tee and repair afterward or replace the pressure hose.

I can't help wondering about the ECU. I have read that it's possible for the ISC to cause the ECU to blow and installation of another ECU without replacing the ISC promptly caused the next ECU to blow as well.

I'd be tempted to make friends with a junk yard owner and try to arrange some parts swaps unless someone else has an idea. If you can find a like truck and get the ECU, distributor, coil, ISC, TPS, MAF sensor to try - and pay for anything that works it might be a faster way to eliminate some suspects - particularly if they're breaking down with heat. I hate throwing parts at an engine, but if it can be done without spending a lot of money it might be worth trying.

Frank


'89 [color:"white"]G-Raider[color:"white"] [color:"black"]Supercharged 3.0L, MegaSquirt 2, lockup A/T, 2.5" exhaust, 172k, Cibie H4s/Oscar SCs, Hella Micro DE fogs, Cobra CB, Superwinch hubs, LSD rear/Aussie Locker front, Bilsteins, Lifeline AGM, Rust-Oleum

#620805 - 07/02/05 05:38 AM Re: ISC removal? [Re: FrankR]  
Anonymous
Unregistered

Thanks again for the ideas. I have checked the fuel pressure.

The transistor has been checked but I would be willing to check it again if you would let me know what I need to do.

I'm sure that the coil has been through the check, I would be interested in your direction to check it again also.

I will unplug the AFS tomorrow and see if that changes anything.

The ISC was not plugged in after the ECU was replaced, so hopefully the ECU repair was correct and not just a partial.

I did try the ISC adjust w/out it plugged in and all it did is change the idle untill it died. Thanks again


#620806 - 07/02/05 06:27 AM Re: ISC removal?  
IdahoJack  Offline
Mudrunner
Joined: Jan 2002
Posts: 457
Weiser, Idaho
Your problem sounds similar to the one I had about a year ago. You might want to read these old posts to see if they might help:
http://tinyurl.com/a5l7r

Last edited by off-roader; 09/10/05 05:34 PM.

90 Montero, 2dr, AT, V6, LSD, AC, KYB shocks, bouncy seat, 182K miles, JDM engine, 87 Starion seats, tow hitch
http://www.geocities.com/idahojack03/Index

#620807 - 07/02/05 01:40 PM Re: ISC removal?  
FrankR  Offline
Web Wheeler
Joined: Feb 2004
Posts: 10,238
Columbia, SC ****
Quote
If I hold the contacts closed in the control relay it will run forever. I have tested the control relay and also tried another one the same results.


I missed that on the first run through. It does sound like IdahoJack's problem - the ECU isn't allowing the fuel pump to run.

Instructions for testing the power transistor are here . Other ideas as well.

Since you're able to keep it running by forcing the control relay, I suspect the ECU as Jack suggests.

Frank


'89 [color:"white"]G-Raider[color:"white"] [color:"black"]Supercharged 3.0L, MegaSquirt 2, lockup A/T, 2.5" exhaust, 172k, Cibie H4s/Oscar SCs, Hella Micro DE fogs, Cobra CB, Superwinch hubs, LSD rear/Aussie Locker front, Bilsteins, Lifeline AGM, Rust-Oleum

#620808 - 07/02/05 06:58 PM Re: ISC removal? [Re: FrankR]  
Anonymous
Unregistered

Thanks Idahojack and Frankr. It does sound like a similar problem and a real positive looking solution. I will make tracks to have this checked next week since everything is closed for the 4th. AVPRO may get it back. The sites that were sent are helpful and saved.

Thanks to all for the direction and I will put the gas and flares away for now.

Happy 4th <img src="/forums/images/graemlins/cheers.gif" alt="" />


#620809 - 07/02/05 07:43 PM Re: ISC removal?  
FrankR  Offline
Web Wheeler
Joined: Feb 2004
Posts: 10,238
Columbia, SC ****
ECUs show up on ebay from time to time. There are a couple there now, but they're too expensive unless you absolutely have to have it now. Try this site and contact a few, but make sure the part number is the same as your own - and get a guarantee that it's a working unit:

carpart.com

I bought one as a spare and from what I've so far seen about these trucks it's probably the best spare part to keep on hand.

If this works, you owe Jack a <img src="/forums/images/graemlins/cheers.gif" alt="" />. Anybody who can find a bad transistor in an ECU gets my vote for at least a 6-pack.

Good luck,
Frank


'89 [color:"white"]G-Raider[color:"white"] [color:"black"]Supercharged 3.0L, MegaSquirt 2, lockup A/T, 2.5" exhaust, 172k, Cibie H4s/Oscar SCs, Hella Micro DE fogs, Cobra CB, Superwinch hubs, LSD rear/Aussie Locker front, Bilsteins, Lifeline AGM, Rust-Oleum

#620810 - 07/10/05 08:07 PM Re: ISC removal? [Re: FrankR]  
Anonymous
Unregistered

Just to update. I checked the AFS and no change. I contacted AVPRO to recheck the computer again and was told he wants a certified tech to suggest this.


#620811 - 07/10/05 10:09 PM Re: ISC removal?  
FrankR  Offline
Web Wheeler
Joined: Feb 2004
Posts: 10,238
Columbia, SC ****
I just spent some time with the electrical portion of the '89 FSM. I haven't had a similar problem but it's a good time to attempt to understand the fuel circuits. There's a lot that happens within the ECU that I can't see without an circuit board diagram but the associated wiring schematic shows two (2) circuits within the control relay:

Current flows from one set of contacts on the MPI control relay to the MAF sensor, the ISC, the purge control solenoid valve, the EGR control solenoid valve, the injectors and the ISC. The trigger for that circuit appears to be the "light green" wire from the ECU to the control relay.

The other set of contacts powers the fuel pump drive terminal with supply voltage from the ignition switch. The trigger appears to be the "white/red" wire from the ECU to the control relay.

You can check voltage on those wires before and after the engine quits to see if there's a change. However I'm very suspicious of the ground connection on the control relay. Check continuity on the "black" wire coming from the control relay to ground. If you read anything other than zero, you may have found the problem. If you're using an analog meter, be sure to first "zero" the meter.

If the control relay harness/connection passes the ground continuity test and there's voltage on the 2 identified relay trigger wires - if it were my truck it would then be time to get out the dynamite. <img src="/forums/images/graemlins/lol.gif" alt="" />

I know there are differences in the '89 ECU and your own, but I don't know what they might be. The setup could be quite different and the wire color markings certainly could be so it would be better to use the manual for your model year. The ground wire on the control relay would be the same "black" color, though. Maybe someone with a '91 manual can verify the wiring as identical or not.... in any event, it won't hurt to measure voltage on those wires.

Good luck,
Frank

Last edited by FrankR; 07/10/05 10:14 PM.

'89 [color:"white"]G-Raider[color:"white"] [color:"black"]Supercharged 3.0L, MegaSquirt 2, lockup A/T, 2.5" exhaust, 172k, Cibie H4s/Oscar SCs, Hella Micro DE fogs, Cobra CB, Superwinch hubs, LSD rear/Aussie Locker front, Bilsteins, Lifeline AGM, Rust-Oleum

#620812 - 07/11/05 06:27 PM Re: ISC removal? [Re: FrankR]  
conner  Offline
Rock Warrior
Joined: Aug 2004
Posts: 644
N.J.
Quote
Anybody who can find a bad transistor in an ECU gets my vote for at least a 6-pack.

Good luck,
Frank

Frank
It is not uncommon for the IAC motors to take out the drivers in Mitsubishi vehicles. Here is a trick that i use to test a transistor for any ECM controlled circuit. Remove the ignition fuse to the ECM. Place an ammeter in place of the fuse. disconnect the componenent (relay, motor etc.) Turn the key on. The meter should read between 4mA to 40mA depending on the transistor and its circuit.
Forget the six pack. I am still waiting on that armed chopper you showed me.
Conner
<img src="/forums/images/graemlins/lol.gif" alt="" /> <img src="/forums/images/graemlins/lol.gif" alt="" />


Over the hill but still climbing.
88 Montero 2.6L auto, manual hubs, cooling fan conversion gps,recurved distributor,LSD Diff.

#620813 - 07/11/05 06:44 PM Re: ISC removal? [Re: conner]  
FrankR  Offline
Web Wheeler
Joined: Feb 2004
Posts: 10,238
Columbia, SC ****
Quote
Here is a trick that i use to test a transistor for any ECM controlled circuit. Remove the ignition fuse to the ECM. Place an ammeter in place of the fuse. disconnect the componenent (relay, motor etc.) Turn the key on. The meter should read between 4mA to 40mA depending on the transistor and its circuit.


So if the ECU is blown, the ammeter would read zero? Is that the idea? If so, you wouldn't know which component was blown, though, would you?

Also, couldn't there still be current draw if one section of an ECU was open and another working correctly?

I've never seen the circuit diagram of an ECU, but did have my spare one apart to look at the board - didn't count the components, though.

Oh - the chopper's back-ordered. <img src="/forums/images/graemlins/lol.gif" alt="" />

Frank


'89 [color:"white"]G-Raider[color:"white"] [color:"black"]Supercharged 3.0L, MegaSquirt 2, lockup A/T, 2.5" exhaust, 172k, Cibie H4s/Oscar SCs, Hella Micro DE fogs, Cobra CB, Superwinch hubs, LSD rear/Aussie Locker front, Bilsteins, Lifeline AGM, Rust-Oleum

#620814 - 07/11/05 06:48 PM Re: ISC removal? [Re: FrankR]  
FrankR  Offline
Web Wheeler
Joined: Feb 2004
Posts: 10,238
Columbia, SC ****
Conner -

If you have a minute or so, take a look at the 3.0L MPI circuit and see if you agree with my thought in the above post... I don't know what else to suggest.

Frank


'89 [color:"white"]G-Raider[color:"white"] [color:"black"]Supercharged 3.0L, MegaSquirt 2, lockup A/T, 2.5" exhaust, 172k, Cibie H4s/Oscar SCs, Hella Micro DE fogs, Cobra CB, Superwinch hubs, LSD rear/Aussie Locker front, Bilsteins, Lifeline AGM, Rust-Oleum

#620815 - 07/11/05 08:56 PM Re: ISC removal? [Re: FrankR]  
conner  Offline
Rock Warrior
Joined: Aug 2004
Posts: 644
N.J.
Quote
So if the ECU is blown, the ammeter would read zero? Is that the idea? If so, you wouldn't know which component was blown, though, would you?

Also, couldn't there still be current draw if one section of an ECU was open and another working correctly?

Oh - the chopper's back-ordered. <img src="/forums/images/graemlins/lol.gif" alt="" />

Frank

Frank Yes, if that paticular driver is bad you will see zero. Later vehicles allow you to active a circuit through the scan tool so you know what you are dealing with. In earlier vehicles, i just look at a wiring schematic and identify what else may be activated at the same time and disconnect those components, Actually a lab scope is the best tool as i can even find a working driver thats not pulling the component all the way to ground.
Hope that chopper makes it on time for hunting season.
Conner


Over the hill but still climbing.
88 Montero 2.6L auto, manual hubs, cooling fan conversion gps,recurved distributor,LSD Diff.

#620816 - 07/16/05 11:58 AM Re: ISC removal? [Re: conner]  
Anonymous
Unregistered

Another update for this 91 monty. Took ECU to local Mits dealer and had them send it to their preferred repair tech for diag. Comes back with repair needed on fuel pump circ and idle circ. <img src="/forums/images/graemlins/angry.gif" alt="" /> So for no reply from Avpro who was suppose to fix it. Didn't mind taking my $150 though. I know the ISC is bad and I am going to replace it. I have checked the TPS and it seems to be OK. Is there a way to check the idle switch that is in the TPS? <img src="/forums/images/graemlins/scared.gif" alt="" /> I may have another 4th of July in August <img src="/forums/images/graemlins/patriot.gif" alt="" />


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