Adventure Driven Talk

Tech Questions and How-To Articles => Mitsubishi Related => Gen 3 Montero => Topic started by: concealer404 on September 27, 2017, 03:32:33 PM

Title: MAP sensor reporting boost under load/truck stalling
Post by: concealer404 on September 27, 2017, 03:32:33 PM
Troubleshooting a weird thing that has started happening in the last 2-3 days on Wife's 2003 Montero.

At a stop, in gear, with a/c on, it's stalling. 

Will not stall if in park, though idle gets a bit low.

No CELs being reported, no codes.

I was driving it on Saturday and it lost power twice for about 1-2 seconds each time.  Truck seemed to stay running, but just went "flat" if that makes sense.

Does not seem to stall if a/c is off. 

A/C still works great.

OBDII reader through Torque Lite is reporting up to 27psi of "boost" through the MAP sensor every time you put your foot in it.  Idle/low load cruise vacuum looks normal.  Normally i'd say for SURE that the MAP is bad, but knowing that these are weird trucks and Mitsubishi is well.... Mitsubishi, i suppose it's possible that they suck at implementing OBDII PIDs.  Anyone else check MAP with Torque Lite and come up with a bunch of boost?
Title: Re: MAP sensor reporting boost under load/truck stalling
Post by: Crumb on September 27, 2017, 04:39:01 PM
 Defiantly weird, other it reading boost the symptoms sound like a large vacuum leak.
Title: Re: MAP sensor reporting boost under load/truck stalling
Post by: concealer404 on September 27, 2017, 04:44:34 PM
Defiantly weird, other it reading boost the symptoms sound like a large vacuum leak.

Kindof, if it weren't extremely intermittent.  A big vacuum leak would return a code as well, as it would cause a lean condition.

BTW i posted a copy of this thread in the wrong section the other day. Feel free to delete.  :)
Title: Re: MAP sensor reporting boost under load/truck stalling
Post by: IncorpoRatedX on September 27, 2017, 08:07:16 PM
I have no experience with this on the montero but i've seen GM map sensors fail on tuned up boosted mitsu's running speed density and it's done stuff like that, read a crazy high value without change once engine vac is lost (pedal to floor drops the inlet manifold vac until the rpms are up high or boost comes on, but you got no boost) so I would suspect a faulty map, fsm should tell you how to pin it out, good luck, let us know what happens.

i'll delete the other thread.
Title: Re: MAP sensor reporting boost under load/truck stalling
Post by: Kevin_Slark on October 05, 2017, 01:32:30 PM
Any luck on this? I think Adam is on the right track with this one.
Title: Re: MAP sensor reporting boost under load/truck stalling
Post by: concealer404 on October 05, 2017, 01:56:49 PM
It was the MAF.

Vacuum leaks aren't intermittent.
Title: Re: MAP sensor reporting boost under load/truck stalling
Post by: concealer404 on October 11, 2017, 05:32:52 AM
Well, MAF fixed it for about a week and a half.

Now it's stalling again, losing power while attempting to drive, and often refuses to start.  Stranded my wife this morning, have to have it towed.

STILL no codes.
Title: Re: MAP sensor reporting boost under load/truck stalling
Post by: PajEvo on October 11, 2017, 06:21:35 AM
Ah crap. That bites. FSM mentions 15 minutes of steady idle after battery is disconnected to relearn idle. Dont' suppose if could be as simple as that? Assume you know of "mitsubishi links" and Bill's excellent work of compiling all the factory service manuals?
Title: Re: MAP sensor reporting boost under load/truck stalling
Post by: concealer404 on October 11, 2017, 06:57:56 AM
Ah crap. That bites. FSM mentions 15 minutes of steady idle after battery is disconnected to relearn idle. Dont' suppose if could be as simple as that? Assume you know of "mitsubishi links" and Bill's excellent work of compiling all the factory service manuals?

It's been driving for a week and a half since the MAF was replaced with no issues, i think i let it idle in the driveway for about 30 minutes after i replaced it.  This is something new, since it's dying while driving and not restarting.

Since it's not throwing codes, all i can do is throw parts at it.  Don't have records of pump or fuel filter, so i guess i'm blowing some money on that.

Also, no, i haven't seen mitsubishi links.  Flying kinda blind here.  I have a Hayne's "Pajero" manual but it's kinda bleh.
Title: Re: MAP sensor reporting boost under load/truck stalling
Post by: haolepinoy on October 11, 2017, 07:49:41 AM
Concealer, I've been round and round with this issue on my '03. Check your fuel trims to get a handle on where to start. My Montero has never thrown a MIL code for this exact stalling issue, so you cannot expect the PCM to help you. You'll have to get the info yourself with the use of the scanner. With fuel trim data you can figure out if a sensor is actually misreporting (usually won't cause a MIL unless it is way out of spec), if it is and air or fuel issue (a bad fuel pressure regulator or bad vacuum leak for example), if it is confined to one bank or not (super helpful to rule out things)...all with a few simple data readings from your short and long-term fuel trims.

I started several threads about this issue over on ExPo over a year ago and couldn't get any help. I've tried to figure it out myself with the help of the FSM and have learned a lot (but am still a novice) about Mitsubishi electronics and basic auto diagnostics diy. I've tested almost everything affecting the idle on the Montero using the Factory Service Manual techniques and found almost all of my sensors, actuators, and solenoids are fine (big money saver). The main things I've found in my case causing my fuel trim readings were a cracked exhaust manifold and lots of vacuum leaks (dry-rotted hoses, gaskets, etc.). Can't say I've fixed everything yet (that's a much longer story...my Monty has a lot more issues than just this and I'm trying to whack them all at once), but at least I'm sure of what the issue is not. The beginning of this thread (http://forum.expeditionportal.com/threads/158781-How-is-the-idle-controlled-on-a-2003-(3-8L)-Gen3-Monty?p=2379509#post2379509) is me not really knowing anything...the recent post is after getting serious about solving the issue. Offroadmuch is in a similar boat.

Here's another post about how the issue first arose and my attempts to throw my limited knowledge at it http://forum.expeditionportal.com/threads/158784-A-story-about-slaying-electrical-gremlins/page2?highlight=story+electrical+gremlins

Hoping to save you some time and money, plus I have empathy on this issue. A year ago I thought I was the only person in the world suffering from it (I google'd the crap out of this for a long time and found almost nothing), but now it seems to be becoming a common affliction (especially with '03s for some reason). I want to figure out the exact cause and put it to rest. There's literally dozens of other sensors, actuators, solenoids, hoses, relays, etc. that affect the idle on this thing. You can spend a lot of money in a hurry if you don't take a more methodical approach. And I wouldn't trust a mechanic you don't know to take this approach either...they tend to just come up with simple theories and throw parts too.

An hour or so on Schrodingers Box or ScannerDanner's YouTube channels can teach you the basics of understanding fuel trim data. I prefer Schrodingers Box's two part "Secret of Engine Problem Diagnosis - Fuel Trims". Cheers and good luck.

p.s. - Is this the same '03 that is for sale, the Anniversary Black on Black?
Title: Re: MAP sensor reporting boost under load/truck stalling
Post by: haolepinoy on October 11, 2017, 08:00:07 AM


It's been driving for a week and a half since the MAF was replaced with no issues, i think i let it idle in the driveway for about 30 minutes after i replaced it.  This is something new, since it's dying while driving and not restarting.

Since it's not throwing codes, all i can do is throw parts at it.  Don't have records of pump or fuel filter, so i guess i'm blowing some money on that.

I had a similar issue happen to me this spring. Montero would die decelerating, had trouble restarting, strange idles. I found it to be an issue with my Crank Pos Sensor connection on top of the thermostat housing.  I don't think the sensor was bad, but after wiggling the connector the idle would clear up and the restarting issues would go away. My Montero went under the knife shortly after this though (I haven't driven it since April), so I cannot say that it was definitely the problem or that it was solved through the connector wiggle long-term.
Title: Re: MAP sensor reporting boost under load/truck stalling
Post by: concealer404 on October 11, 2017, 08:41:39 AM
Yep same one for sale, unfortunately.   Largely been pretty trouble-free in our ownership other than finding out that the timing belt hadn't been done despite being told that it had by the PO.  Started acting up right after i decided to sell it.  Go figure.

I'll check fuel trims again, though i didn't see anything weird last time.  I read your post over on Expo earlier this morning.  :)  Unfortunately, i don't have time to deal with buying and learning how to use a scanner like that, and then messing around with this truck.  It's my wife's DD, and i have more than enough projects i'd rather spend what little free time i have on.  It'll hit my driveway in a day or two after the shop that's towing it warrantees their VC gasket replacement job, i'll jack into it with the OBD2 bluetooth reader i have, check trims, and if they're messed up, i'll do a basic vacuum leak test, throw a pump/filter at it.

If it's still acting up after that, i'll have to send it to the dealership and pull the FS ad, since i won't be able to afford to sell it anymore after that.
Title: Re: MAP sensor reporting boost under load/truck stalling
Post by: concealer404 on October 12, 2017, 06:23:06 AM
'Tis fuel pump.

New Denso pump, strainer, and filter being delivered tomorrow.
Title: Re: MAP sensor reporting boost under load/truck stalling
Post by: haolepinoy on October 12, 2017, 06:47:37 AM
How'd you determine that? Curious because that's something I've been suspect of as well (even bought a fuel rail adapter to check pressures once my engine is back together).
Title: Re: MAP sensor reporting boost under load/truck stalling
Post by: concealer404 on October 12, 2017, 08:22:36 AM
How'd you determine that? Curious because that's something I've been suspect of as well (even bought a fuel rail adapter to check pressures once my engine is back together).

Starts fine and runs for a short while if you do a poor man's prime (turn key to "On," cycle off, back to "On," cycle off, back to "On," then start), and shop that towed it checked pressure for me.  Symptoms make sense.

I think i got lucky and had two different issues, though.  Symptoms were different this time (fuel pump) than last time (MAF fixed it last time.)

Now i get to add "new fuel pump" to the list of recent work in the FS ad.  :)
Title: Re: MAP sensor reporting boost under load/truck stalling
Post by: concealer404 on October 18, 2017, 05:47:43 AM
Maybe not fuel pump.  Fuel pump was replaced (allegedly), wife picked it up from the shop (who also diagnosed "100% sure" without prompting from me that it was fuel pump), drove it to work with no problems.  And it stranded her again that night.

Currently en route back to me on a flatbed.  Reporting maxed out fuel trims through OBD2 at 25%.  In the 10 minutes i spent poking around it in the dark, i found a spark plug wire that wasn't seated, and the PCV hose to the intake wasn't connected.  Neither of which fixed the problem, but apparently i have to go through this with a fine tooth comb again, since someone else has been in the engine bay.

Yayyyyyyyy.

So far we've replaced:
Fuel pump
Fuel filter
MAF
MAP

I'm running to get a fuel pressure tester today i guess.  I have my doubts that the pump job was done properly, seeing some of the other stuff they did.  Or maybe at all, since the 15 years of dust/grime at hanger hat look pretty improbably undisturbed.  Still no CEL or codes of any kind being reported.

Real life footage captured of the ECU in this truck:
(https://i.imgur.com/mtGc7Sl.gif)


(https://farm5.staticflickr.com/4443/37773227891_95900c9d61_b.jpg) (https://flic.kr/p/ZxTEDR)stupid montero (https://flic.kr/p/ZxTEDR) by concealer404 (https://www.flickr.com/photos/66868738@N05/), on Flickr
Title: Re: MAP sensor reporting boost under load/truck stalling
Post by: concealer404 on October 20, 2017, 06:11:01 PM
Ok so after figuring out that 1) This thing doesn't prime when the key is turned to ON, because it's not supposed to (neat!), and that 2) it has TWO fuel pump relays (FML), i've discovered a few things.

A) Fuel pump turns on, has power
2) Still doesn't run for more than a few seconds at a time, and cranks for a LONNNGGGG time
iii) Does not make fuel pressure, after about 30 seconds of running the pump (jumped at relay #2) it generated a whopping 3-4psi.  Backed up by not much fuel spraying around when the test adapter was removed.
iii.5) still didn't make fuel pressure when the return line was clamped closed with some pliers.

Basically.... pump works (at least as far as i can tell so far), but isn't pressurizing the system.  I suspect a botched install.  Will pull the pump in the morning and investigate.  Good thing i paid a shop to do all this, right?  :unamused:
Title: Re: MAP sensor reporting boost under load/truck stalling
Post by: concealer404 on October 21, 2017, 06:18:52 PM
Today i learned that Gen3 Monteros run way better when they have gas in them.
Title: Re: MAP sensor reporting boost under load/truck stalling
Post by: JohnnyBfromPeoria on October 21, 2017, 11:21:02 PM
Today i learned that Gen3 Monteros run way better when they have gas in them.

Uh oh...say it wasn't so...

John B.
Title: Re: MAP sensor reporting boost under load/truck stalling
Post by: Monstero on October 22, 2017, 03:45:29 PM
I have had same issue with mine for over a year now and have thrown parts and have seen nothing positive happen. The one common denominator for me is the delayed start. I can crank and crank forever. The common denominator for me is that it will always be a hard start after 60degrees outside. and if its 35 degrees outside at night forget it starting. over the summer and warmer months it started just fine and had same symptoms as you had above....such as hesitation while running....blips here and there like it would cut off and on briefly...would stall at idle sometimes... I have replaced fuel pump relays, MAF, fuel pump and filter,brand new crank position sensor, new camshaft position sensor(a PITA to install BTW), a new Engine coolant temp sensor,  and all to no avail. NOTHING has worked. Just recently i thought forsure it was MAF and checked that and then it still delayed start.

I have a block heater on mine so I have plugged it in when temps drop to keep me going, but if i am anywhere too long and it sits in the cold i am screwed. VERY VERY Frustrating because i am usually a person that can troubleshoot and figure this out and havent been able to  for over a year now. Next thing I was thinking it could be was the Throttle body, but there is nothing temperature dependant in there. So I am not sure. Just following and googling and more googling and more scouring trying to find any bit of info that would pertain to it.