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My 1999 Mitsubishi Montero sport ls 2wd 3.0 6cyl runs good…

Customer Question
My 1999 Mitsubishi Montero...

My 1999 Mitsubishi Montero sport ls 2wd 3.0 6cyl runs good when it's cold and then as soon as it reaches normal temperature starts stalling or gagging what could be the problem? DO I NEED TO REPLACE THE RADIATOR ? WHAT COULD BE THE PROBLEM?

Mechanic's Assistant: Is the check engine light on? Does the car stall at idle or when driving?

IT DOESN'T STALL JUST STARTS GAGGING I JUST REBUILT THE ENGINE ON IT?

Mechanic's Assistant: Are you fixing your Montero Sport yourself? What have you tried so far?

I INSTALLED A NEW AIR IDLE CONTROL VALVE ,THROTTLE POSITION SENSOR WHEN I REBUILT I PUT IN NEW LIFTERS,NEW PISTON RINGS ,REBUILT HEAD ENGINE RESET THE VALVES?

Mechanic's Assistant: Anything else you want the mechanic to know before I connect you?

I PUT IN A NEW WATER PUMP AND PUT IN A BRAND NEW TIMING BELT RESET THE TIMING IT RUNS GOOD WHEN IT IS COLD BUT WHEN IT REACHES NORMAL TEMPERATURE STARTS GAGGING WANT TO KNOW WHAT IS CAUSING THAT TO HAPPEN?

Submitted: 1 month ago.Category: Mitsubishi
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Customer reply replied 1 month ago
no supporting documents just want an answer to question I have already paid for.
Answered in 29 minutes by:
3/15/2018
Mitsubishi Mechanic: 350matt, Engineer replied 1 month ago
350matt
350matt, Engineer
Category: Mitsubishi
Satisfied Customers: 22,898
Experience: Mechanical Engineer BEng Hons22 years experience in car engine industry, 10 years in formula 1
Verified

Hello and welcome to Just Answer

can you tell me if the engine is using / losing any coolant?

if so then this may indicate that the head gasket is faulty as I've known this to introduce water into the combustion chamber which then produces a misfire

If you were to do a compression test across all cylinders ? as they should all be within 10-15 psi of each other

and a leaking head gasket usually has a 1 or more low cylinders

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Customer reply replied 1 month ago
no it is not losing or using any coolant, I did a compression test and all six cylinders were 120 psi.
Customer reply replied 1 month ago
I also put in new head gaskets,
Mitsubishi Mechanic: 350matt, Engineer replied 1 month ago

OK

in that case lets investigate the engine electrical system

This could be a wiring issue as things tend to expand when hot and its possible a poor or partial electrical connection is being pushed apart on one of the major sensors so check the connection plug and wiring to the following;
Airflow meter
Crank position sensor
Cam position sensor
O2 sensor
Throttle position sensor

unplug each in turn and use some switch / contact cleaner spray on the pins to ensure its all grease / dirt free

Also worth checking the connections to the fuel pump for the same reason - unplug each in turn and give them a good squirt of switch / contact cleaner - Not WD40

and also unplug and inspect the main power relays and fuses for signs of overheating or corroded terminals - so the ones for the ECU and the fuel pump

And also unplug the wiring loom connections in the engine bay one at time and inspect for corroded or recessed pins.

Check the resistance of the spark plug leads ( 13-15Kohm / metre) and replace if any doubt or high resistance - Also replace the spark plugs if any of them fail this checklist:

https://www.ngksparkplugs.com/about-ngk/faqs/spark-plug-faqs/how-do-i-read-a-spark-plug

Also its worth checking that the electric pump that feeds the injectors is working correctly, it should run for a few seconds then switch off when you first turn the ignition on. If the connections to this are corroded or damaged then the pump could stop at any time. Check that its relay switches in and out and the relay contacts are clean and bright – replace the relay if in any doubt and do the same for the fuse, ideally measure the voltage at the pump and check its getting 12V

Also check for exhaust leaks before the o2 sensor as if this has been experiencing an exhaust leak then it will have been running very rich as the sensor will see the extra air pulled in as fresh / lean fuelling and be adding fuel to compensate.

this can lead to catalyst failure as the extra fuel can re-light inside and melt the catalyst

The best way to find an exhaust leak is to run the engine from cold and feel around the exhaust joints with your bare hands - you'll have about 30 seconds before it all gets too hot and you should feel any escaping gas blowing over your fingers

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Mitsubishi Mechanic: 350matt, Engineer replied 28 days ago

Hi
do you still need help?
Bear in mind that the site takes a deposit from you at the beginning and this is held by the site until you rate my answer at which point the cash is split between the site and the expert. I am only paid for my work on this question if you rate my answer, using the star system at the top of the screen. Please do not forget! If you're not pleased, also let me know because rating bad does not result in a refund, there are better options. Rating now will not close this post nor prevent further replies
Thanks Matt

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350matt
350matt
350matt, Engineer
Category: Mitsubishi
Satisfied Customers: 22,898
22,898 Satisfied Customers
Experience: Mechanical Engineer BEng Hons22 years experience in car engine industry, 10 years in formula 1

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