Running lean..... in warm weather?

[mightymax37110]

My father recently passed down his 93 mighty max to me since I'm recently out of prison and starting over. Well it needed a mass airflow sensor, after replacing it ran great. In the winter weather. Now that it's warmed up some outside in the great state of TN, in warm weather, and after it has reached normal operating temperature it runs lean. This is by the way a 93 mighty max 2.4

Anybody have any idea of what is causing this? I'm stumped. Between my dad and myself we have 60+ years of mechanic experience and neither one of us can figure it out. I found your site and joined in hopes someone, anyone can help me out.

[mightymax37110]

My father recently passed down his 93 mighty max to me since I'm recently out of prison and starting over. Well it needed a mass airflow sensor, after replacing it ran great. In the winter weather. Now that it's warmed up some outside in the great state of TN, in warm weather, and after it has reached normal operating temperature it runs lean is is by the way a 93 mighty max 2.4

Anybody have any idea of what is causing this? I'm stumped. Between my dad and myself we have 60+ years of mechanic experience and neither one of us can figure it out. I found your site and joined in hopes someone, anyone can help me out.

Sorry guys. Was supposed to say lean not rich.

[royster]

I'm gonna guess throttle position sensor.

[mightymax37110]

I'm gonna guess throttle position sensor.

TPS? In cold weather it runs fine. I don't understand how that could be the TPS.
I also left off, if it starts doing it while driving, I can push the clutch in,a completely turn off the ignition, let it coast for about 5 - 10 seconds, turn ignition back to on position and let out of the clutch, it runs good again for a few minutes

[pennyman1]

It sounds like bad caps in the ECM - there are threads on here on what to look for and how to change them out.

[geezer101]

Hmmm, what is your ignition coil like? I think this is one of those 'snowball' things. I'll throw my hypothesis at this - coil is tired, starting to break down. Engine senses a change and attempts to tune it out. An electronic ignition coil is good for about 10-15 years before it starts to drop output.

[mightymax37110]

It's the original coil, but the analog multimeter kept popping for ecu.mass airflow. Internal air temp switch. Keep in mind it's a brand new (remanned) cardone maf

[mightymax37110]

Does anyone have the links to the threads about replacing caps in the ECU?

[DroppedMitsu]

Fixed thread title and post for you. I got nothing on the issue right now, I'll think on it and let you know

[mightymax37110]

Fixed thread title and post for you. I got nothing on the issue right now, I'll think on it and let you know

Thank you

[mightymax37110]

Tps checked fine. Now it is doing it in any outside air temp as soon as it gets to normal operating temp. Coolant temp sensor, coolant temp switch, and temp sending unit are all functional. Has to be in the ECU correct? Would taking the thermostat out and running it without one stop this issue?

[DroppedMitsu]

Definitely sounds like the ECU, some capacitors probably started leaking or something else funny happened.

[mightymax37110]

Board
16040
(click image to enlarge)

[BradMph]

We have a manual on these ECU and how to repair them.

http://www.mightyram50.net/vbulletin/showthread.php/3275-Repair-and-Rebuild-Mitsubishi-ECMs-and-ECU-s

[geezer101]

I'm looking at that ECU board and it is a mess. Like it's been exposed to salt water...

[mightymax37110]

Replaced ecu with working ecu, still same issue. But come to find out it isn't leaning out, when it bogs it's actually losing fire. So would that be the little black box on the engine or the coil itself?

[geezer101]

Hmm, coil issue? If it was the ignitor module the engine would be dead (well, I think - unless it is loading up and getting hot, then misfiring)

[mightymax37110]

I've narrowed it down to the fuel pump. 99% sure it's surging when it gets hot

[mightymax37110]

Ok. Well after putting a fuel pressure test gauge on it and running it for an hour it ran great. barked 3rd gear on dry pavement, then I removed the test gauge, and here we go again. What am I missing? Anybody? Somebody?

[geezer101]

What was the fuel pressure like with the gauge on? Might be a pressure regulator issue(?) It doesn't explain why it ran great with the test gauge hooked up...

[mightymax37110]

It was staying steady at 38 psi at idle. slowly press the throttle and it would raise to about 45 - 50 psi. Blip the throttle quick and the pressure would drop but not lower than 28 psi. As soon as i removed the gauge and took off down the road it went to starving for fuel again.

[pennyman1]

there is something wrong there - an electric pump shouldn't fluctuate that much on pressure. I would try the regulator first, then the pump.

[mightymax37110]

I still think it has something to do with something else. today when it was over 70 degrees out it would starve for fuel, after it reached normal operating temp. But tonight it is fairly chilly outside and it runs fine. When it runs fine the temp gauge stays below normal. When it does it, it stays just above normal operating temp.

[geezer101]

Try something stupid - leave the fuel cap off. My brother had a Mitsubishi Scorpion that would bug out in hot weather - it would run like crap like it was...starving of fuel (it was a carb'd 4G52 engine). I figured out that the fuel tank would build vacuum for some unknown reason. Opening the cap released the vacuum and next minute it would run perfectly.

[mightymax37110]

Already checked evap. Seems to.be functioning correctly. Although I didnt check the.gas cap. I swear if that's all it is I'm gonna be mad lol

[geezer101]

Sorry, I just had a memory jolt. It didn't build vacuum, it would pressurise - but it still killed the engine. I remember now that when the engine died and I cracked the gas cap open, a huge surge of fuel vapour would erupt at me! Lucky I'm a non smoker lol

[mightymax37110]

Mine does that exact same thing

[BradMph]

Already checked evap. Seems to.be functioning correctly. Although I didnt check the.gas cap. I swear if that's all it is I'm gonna be mad lol

Don't feel bad, I seen many people kicking themselves when they find out the real problem was something overlooked.

16085

[mightymax37110]

Installed new fuel pump/higher pressure unit. And when it hits normal operating temp it still acts like it a sstarving for fuel

[BradMph]

Sorry, I just had a memory jolt. It didn't build vacuum, it would pressurise - but it still killed the engine. I remember now that when the engine died and I cracked the gas cap open, a huge surge of fuel vapour would erupt at me! Lucky I'm a non smoker lol

Geezer, was your charcoal canister not working? You probably caused about 6 months of global warming with that vapor loss huh, lol

[geezer101]

Geezer, was your charcoal canister not working? You probably caused about 6 months of global warming with that vapor loss huh, lol

Not my car Brad! :lmao:My eediot bro abused that poor thing. I mean, he beat on it with a dead water pump, never changed the oil, never cleaned it - nada. It finally was put out of it's misery when he attempted to climb a 5 storey high tension power pole with it one night. The battery landed on the footpath 20 metres down the road...

Anyhoo, someone got insight into mightymax's fuelling issue yet? :scratchheadyellow:

[mightymax37110]

Question, how often to the vacuum servos on the fender wall go bad?

[claych]

mm37,
??? have You re-run a code check ???
Specifically code 13 , 21 , 25.
Thx

[mightymax37110]

Last code check said motor position sensor and mass airflow sensor. But maas airflow is brand new

[claych]

With respects, according to Your posted info, the M.A.F. is a 'reman' unit.
-reman is NOT new- !
& You have changed the ECU because the original looked " like it was submerged in salt water"...
& Still have code 13 ?

Thx, not trying to be an azz, just trying to help... web diag sucks ...

[mightymax37110]

Problem found and fixed. Idle air speed sensor.

[BradMph]

And another happy customer finds the problem and fixes it. Congrats! :)