1990 Montero dies when pressing gas....

normal_dave

waytoomuchwritinginposts.
Since it has run this way since you bought it, maybe...just maybe the PO tried to mess with the timing without grounding the plug under the wiper motor. Then the ECU tries to overcome the incorrect initial timing.

If not, well, then you've eliminated another possibility, narrowing the search.

Here's a good read on setting the timing on your truck:
http://www.4x4wire.com/forums/ubbthreads.php/topics/1035268/1.html

more regarding timing belt, but also cover distributor and the tricky #1 spot under the distributor cap
https://www2.pajeroclub.com.au/forum/showthread.php?t=25948
 
Hey folks... Still no change. Im literally at my wits end here. I've been working on vehicles for years. I've had several mechanic friends over. No go.

Report to date...

It's hard to start. Takes turning it over a dozen times or so then it will fire up, rev high and then die, then turn it over again once or twice and it will start. It won't stay running for any real length of time. I can keep it running by quickly tapping the gas pedal or quickly moving the throttle cable if Im under the hood. As soon as you give the gas pedal a real push it dies.

Normal Dave: The hard part about checking the timing is I can't keep it running long enough to read...
 

normal_dave

waytoomuchwritinginposts.
Still think you may need to seek qualified, professional help, but with that said:

First time I've heard about the revving up high at idle, takes me right back to a bad ISC/IAC motor. What happens when you try to run it with the TPS unplugged? I read these motors run a little high until engine temp comes up, then drops to normal, but lots of issues with continued high or fluctuating idle speeds, usually related to ISC/IAC.

Have you taken a can of starter fluid or similar and sprayed around your intake gaskets, throttle body, brake booster vac line, and vacuum line connections etc? If you have a bad vacuum leak you'll get a change in engine speed at the point of contact of the spray.

As far as the timing, you could verify everything is lined up mechanically, engine not running, crank TDC#1/camshaft marks/distributor/rotor pointing to firewall (at visual #2 position, which is really #1)

Edit: since you are at your wits end, lets have an old-school adventure:

-Clean the base of your distributor and the surrounding block.
-Mark an index line from the distributor base out to the block. (chalk, sharpie, paint marker, etc.)
-Loosen the distributor clamp just enough so that you can turn the distributor with one hand.
-Find the diagnostic plug for your timing and ground it. Look it up, but I think it is in the harness on the firewall somewhere under the wiper motor.
-If needed, get a helper to start the engine, (don't press the gas ha ha) slowly turn the distributor up to 10 degrees in either direction. Picture the top of the distributor in the 360 circle when looking down.
See what happens to the idle. Advancing the distributor in the direction of rotation should increase the idle a little, retarding in the opposite direction should drop it back a little. Too far advanced will start to cause rougher/skipping engine after max idle is reached. Too far retarded will stumble and stall after lowest idle is reached.

In the old days, when we didn't have access to a timing light, we used this method along with a vacuum gauge to set the timing. Generally we'd turn it (the distributor) towards max idle speed, and/or highest vacuum, engine just starting to skip then back it down about 5 degrees or so and tighten the clamp.
After all this fooling around, if nothing is found, then return the distributor to your original mark, tighten clamp, unplug diagnostic ground, and you are back to square one, and you have verified the timing was ok, or really off the mark.
If you find the timing was off really bad, you could adjust the distributor (advance it) to the max idle, then bring it back down until there is no spark knock (detonation) when driving, if you get that far.
All of this is useless unless you ground the proper connector to remove computer control from the timing.

It sounds like until you get a reliable smooth idle, it's not worth pursuing the pressing the gas problem.
(end edit)

Let's not assume since you checked an item once that it isn't still bad. These mysteries can be really frustrating. I've had times where I had to start over from scratch, take out the legal pad, and start writing down each step of troubleshooting, because I would make assumptions, but when I wrote it down, and read over each step, then sometimes I would see things I hadn't thought of before.
 
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Normal Dave: Thanks for the thorough answer, super appreciative of that. I'll report back. Fingers crossed. As for the qualified help, Ive had that in the form of multiple friends who are mechanics, they're as baffled as I am. I can't see taking it to a garage at this point, I'm guessing they won't know much of what to do...

If anyone in the Seattle area has a Mitsu mechanic recommendation shoot it on over!
 
Got some headway... So, I unplugged the MAF Sensor and she runs!! Only problem now is it's not the MAF sensor. I have one on my running Montero and then two spares all of which work. I tried all 3, if its plugged in it starts and dies. If left unplugged it idles.

Seems electrical (in the plug for the MAF) which worries the hell out of me if true. Or could be a major vacuum leak (my guess or hope?)


Any thoughts here?
 
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IncorpoRatedX

Explorer
have you checked your fuel pressure?

A dying pump will often supply enough fuel to idle but not enough to drive. Just a thought.

unhooking the maf will make the ecu go into 'limp mode' which could make it run better by locking the timing at 5* if the 90 ecu's did that. they did it on the 4 cylinder MPI engines.
 
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yootahrunner

New member
Bumping this from the depths. Just bought a g1 Montero with this issue. Have some avenues to explore but wanted to see if OP ever worked it out.
 

Joe2Slow

New member
I had some similar issues with my '90 Montero about 8 years ago. So about the same time, coincidentally, as the OP. Though this was not my only issue. I'm not nearly as experienced as the others in the forum, but one thing an electrician friend helping me found was that my ignition coil was going bad. I got spark, so it didn't appear to be bad, and it worked at idle, but wasn't too happy when I tried to rev up.
 

yootahrunner

New member
I had some similar issues with my '90 Montero about 8 years ago. So about the same time, coincidentally, as the OP. Though this was not my only issue. I'm not nearly as experienced as the others in the forum, but one thing an electrician friend helping me found was that my ignition coil was going bad. I got spark, so it didn't appear to be bad, and it worked at idle, but wasn't too happy when I tried to rev up.
Thanks for adding what it could be! I ran a carfax on mine after I posted that and saw that the ignition module was serviced a few years ago but it wasn't that. I was considering doing the coil and the ignition control module after reading your post but I wanted to double check the basics before I started spending more money. Turns out I got lucky!

For those who wander here in the future with this issue, in my situation it was bad gas. I thought I had purged enough of it when I changed the fuel filter but I guess not. I had about 3 gallons of gas in the tank and decided to dump a whole bottle of Techron (choose your fuel system cleaner) into the tank and let it sit for a few hours to do some errands. I went to start it up and just like before, it would start up and once the idle kicked down, it would struggle and stall. The second start up though.. it struggled.. and struggled and then kept going!

Went to give it some throttle and nothing.. still bogged down. I let it idle for about 10 minutes and as each minute passed, the motor started getting stronger and stronger. Crazy lifter tick but it was getting better by the minute. Finally it was able to take throttle inputs. I got it to move on its own power and I can't be more thrilled.
 

Oso

Forest Defecator
Didn’t read the previous 20+ replies. I had the same issue with my Gen 1. Fuel pump tested ok. However when I checked fuel pressure it was low. Don’t recall the numbers but it was definitely lower than FSM spec. Swapped in a new one and blew out the lines to be safe. Fixed. HTH. Good luck.
 

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