Hello, people,
On a 2000 Montero Sport, 3.5L, 2WD, with 204K miles,...
It started Missing about 2 months ago, and has gradually gotten worse.
Now, it Misses every few minutes, And... a few times a day, it misses
many times in rapid succession, to where it feels like I'm driving on
a rough road for a second or two. And, the Check-Engine-Light is Not on.
I've owned it for 2 years; I don't know when the last tuneup was done.
The mechanic hooked it up to his computer, said everything looks good.
He figured: "New Plugs and Wires should fix it".
$390 later, it runs just the same. No improvement.
The Mechanic now just wants to wait until the CEL comes on, so then
he'll know where the problem might be. I don't really want to wait.
Have you experts got any clues?
Maybe it's not even a Miss? But that's what it feels like.
Thanks very much for any advice.
Mark53

 

It is difficult to point you in the right direction without going on the wild hare hunt. Without DTC codes it is a guessing game - which is what your mechanic did. What is surprising is that he just went for the "shot in the dark" with the plugs and wires stand by. Even without CEL, even a simple diagnostic software can confirm or dismiss the fact that you have a misfire. Also, he should have been able to see the fuel trims for the system to see if it runs super rich or super lean. This can be due to a vacuum leak, injector malfunction or other reasons. Do you experience the "misfire" condition when you are at idle or more when you are on the highway at higher RPMs? It is possible that your fuel system is not delivering enough fuel (bad/weak fuel pump or plugged fuel filter). Check fuel pressure to see if it is within norm. Please do not start throwing parts at the truck. Make sure mechanic (or you yourself) first confirm a malfunctioning part/system first before swapping parts.

 

Thanks for the reply, Hunter.
When I got the vehicle from the mechanic, he said that when it was hooked up
to the computer, he did see that nothing was running Too rich or Too lean.
He said a couple of the cylinders have a bit low compression, but not at all Bad.
He mentioned that the problem might be 1 (or more) of the 3 coils.
He calls it a "rough idle", but I haven't really noticed a problem at idle.
I notice it while cruising or gently accelerating at 30 to 50 MPH.
Thanks for the advice to not "throw parts" at it. I Like that idea.
OK... when I can, I'll check the fuel pressure. What should it be?
Thanks.

 

And... I think he opted for that Plugs and Wires solution because I don't know when they were previously done.
The only regular maintenance that I've done in the 2 years (and 28K miles) of owning it is to add oil.
Again, Thanks for any ideas.

 

Hi Mark53, looking at your previous post, you said mechanic thought the issue might be related to the ignition coils. He should be able to see the wave form on the coils with the help of a scantool and confirm that a coil(s) may not function within specs. I'm still puzzled by the fact that no DTC is set.
As far as fuel pressure, I'm sorry but I do not know the value for your vehicle's year/model. I don't think you'll be able to test it on your own. You need an adapter for that and they are not easy to come by.

 

Thanks for your input, Hunter.
A friend has a machine shop, and he has a fuel pressure tester thingy.
I used it on my son's Jeep... very easy to attach / test.
I cannot see on the Montero where to hook it up.
Do I need to remove that "intake manifold" / plenum thing?

I put some fuel injector cleaner in... no improvement yet.

However... here's a new clue...
I noticed that the vehicle does not miss at all when it's cold.
Of course, after 3 or 4 miles, it's warmed up, and it starts missing.
I don't know what that means, but it Must mean something.
Any ideas?

Thanks.

 

My guess, dirty injectors and/or faulty injectors. It could be anything from coil failing to charge enough for a spark to a dirty injector plug. It could even be the ECM failing to energize the injector circuit.

Do the simple stuff first, clean the coils connector, clean the injectors conector and clean the grounding points near the battery and engine. With a good enough OBD2 scanner you should be able to run a misfire counter while driving to see which cylinder misses. Also, before using injector cleaner in the tank, change the fuel filter, what use is a injector cleaner if the first thing it passes is dirty. Now I'm not saying it's the fuel filter but it could be. Injectors could be temporarily clogging with dirt, making it miss then unclogging after 2 or 3 duty cycles.

 

Unfortunately Monteros don't come with a Schroeder valve on the fuel line (like Jeeps and GM vehicles). You need to add a special adapter where high pressure fuel line feeds into the injector rail to run the test. Those adapters are not easy to come by You do need to do some more diagnostics to zero down on the issue at hand. I agree with ricardo - run the missfire counter to localize the missfires. If you have issue with just one or two cylinders - it is likely an injectors or ignition coil. If it is all over the place - it is more likely fuel, or some other issue. It will take some more digging to figure it out. Starting with a fuel filter change might be a good idea. The fact that misfires happen when engine warms up tells me that it happens when engine is in Closed Loop. This means it can be a sensor malfunction and not ignition or injectors (those would cause misfire happen in Open Loop as well as in Closed Loop). Was your friend able to read fuel trim levels on the engine (STFT and LTFT)? If not, go to O'Railey or Autozone and borrow their OBTII readers. They should be able to read live fuel trim levels even when no DTS codes stored in the system.

 

Very Interesting stuff there, gents.
I've never heard of the Closed or Open loop thing before. So, I just Googled and studied it.
OK... it makes sense that Open and Closed loop IS the difference between when it misses, and when it doesn't.
I read that Heavy acceleration might throw it back into Open loop, even after it's warm.
I'm an old fart, and I drive quite conservatively, mostly just to conserve fuel.
I basically never do that Fast acceleration thing, but I'll try it, just to see if it still misses.

Gary (machine-shop friend) does have an OBD2 scanner... an old Snap-On MT2500 (nicknamed the Brick).
It Does show Misfires on each cylinder of a 2002 Chevy, but it does Not show that info on this 2000 Mitsu.
Gary says that's because the Mitsu computer (ECU/ECM/PCM/VCM) probably doesn't even offer that info.
Do you think that a newer scanner WOULD show that info?

Ricardohd91: IF the problem is the ECM not energizing an injector, then does that mean that I might
need to replace the ECM? THAT's probly more expensive than the value of the vehicle! Eeeek !
I like the idea of cleaning various connectors. How? Just blow them out with an air compressor?

HunterD: Darn... no schroeder valve.
OK,... I'll plan to take it back to the mechanic for further diagnostics.
(Heck... I've paid him $390, with no improvement... I hope he'll cooperate.)
Hopefully, we can determine Which cylinder(s) are misfiring.
I Googled STFT (SHORT term fuel trim and LTFT)... Maybe he can see something valuable there.

Of course, we all know that I'm not an expert here, but I sorta' doubt that it's a Fuel problem.
I think it's an Electrical problem. I don't think that a Fuel problem would make it miss/hesitate
like it does... only at certain times... and when there is Little load being put on the engine.
I'll know more after tomorrow's Fast acceleration test... with Lots of load / fuel demand.

Thanks very much for the continued conversation, guys.

 

I'm a dunce, I remembered an issue we had at a shop where I worked at. 2003 Mitsubishi galant. Random missing. No codes, everything new on the engine. I was diagnosing it, nothing, slammed my hand on the afm (air flow meter) engine missed, hit it again it missed again. Would make sense here to.