1990 Mighty Max Burning too much fuel problem.

So first off Ill just give you guys the short and sweet version.

What I changed:

new oil filter
new oil (20-50 recommended from AutoZone)
New-ish MAF sensor (Old one had that small thermistor burn out)

My check engine light is always on but I cant seem to get the LED trick to work. My truck is a 3-4 time owner so who knows what kind of problems it has had.

One thing I have noticed is when I use the LED probe to see which wires are working, I've checked my mass aif flow sensor wire and the only one that works (light coming on in LED probe) is the big red one (which I assume is the power wire) one other wire barely lights up (very dim). All the rest do not light up. Is that normal? Can someone check to see if their mighty max or d50 is the same? I've been researching off and on for the past week but I cant seem to figure it out. I will post pictures when I get back from work in about 8 hours. Like I said my truck wastes so much gas and the check engine light is on. When the MAF is NOT plugged in, I cant seem to go past 45 MPH and I cant rev the engine too high of a RPM before it throttles back (or what ever. Thanks you guys for any help. I will give a more in-depth summary of what has happened up to this point when i get back.

After replacing a bad head gasket and finding a crack in the head... bought a new Clearwater head and had the injectors ultrasonically cleaned, the truck ran a little better, but still like crap.

The IAC at idle was contactly 'searching'. I pulled it and the TPS and bench tested both within FSM specs. I tried a lot of things too as my truck was only getting about 6 to 7mpg and the brand new iridium plugs and O2 sensor kept getting carboned up quickly.

In the end I took it to a local shop where they hooked up professional vacuum tester that blew smoke through the system and they isolated it to a leaky throttle body.

Got a new throttle body put on and it ran even better, but I still need to pull plugs and o2 sensor again for another cleaning. Truck down currently for a clutch and new exhaust will let you know what comes of it. But look at your vacuum system and if posisble try swapping out your throttle body with a spare or have it tested by a pro shop.

Jim

Ill have to check in that. Also, later on today after I get home from work, Im going to pull out my ECU to see if I shorted something out. Also, I have been reading up on what else can cause poor gas mileage. Wrong oil weight came up and I just started to change my own oil and the oil weight recommended to me was 20-50, which seems a little heavy to me. I live in the Las Vegas, NV area so the temperatures get very high. What oil weight are you guys running if you dont mind me asking?

But on another note here is what has been happening to me when I first got the truck in Feb 2011.

March 2011 Truck ran fine until I used some fuel injection cleaner. Then I couldn't go faster than 35-45 MPH no matter what I did.

April 2011- Went to my local oil change place and paid the guys $20 plus the cost of a fuel filter to replace said fuel filter. Ran great after that.

Dec 2011- Truck started to bog down when I went to step on the gas. For the life of me could not figure out why. Had to tap on the gas to keep up speed. Could not go faster than 50-60 MPH.

Early April 2012- Finally got fed up with truck and started to figure out what went wrong with my truck. Changed fuel filter, O2 sensor, spark plugs, spark plug wires, coolant temp sensor, TPS, oil change. Then by some miracle I was unplugging connections and the mass air flow sensor/meter was unplugged and the truck ran fine. I didnt really notice too big of a mpg change, just happy to go over 50 mph! So I went to the junk yard and found a new MAF sensor and hooked it up.

April 2012 (Present)- Now heres what happened. I hooked the MAF sensor in the connectors but left the MAF sensor my truck and went to start it, I didnt turn it over (ignition) then heard a subtle POP! Turned off truck to see what had happened and saw that little tiny diode/thermistor had blown and now my check engine light was on. Pretty sure the metal on metal shorted it out. So i went to get another MAF sensor and hooked that one up (carefully this time) and the truck runs ok but Im wasting too much fuel. My truck is a little hard to start in the mornings (turns over, dies,turns over , dies ,etc.) before it start to idle. Then like I stated above, went to try and get the codes off the check engine light but with no success using the LED probe trick. Maybe I need to find the ground wires and make sure that they need to be checked but I may need some guidance on where they are.

I apologize about the wall of text but didnt want to leave anything out, even if said stuff makes me look like a retard, just being honest about what happened.

First off go here: and find out what codes the ecu is throwing so u can fix those sensors/problems. That method is very easy and i use it all the time. The error numbers it lists on the site are for an eclipse though so u wil need to find the correct error codes for ur 2.4 in the fsm or haynes/chilton manual

Like I stated in my first post I cant seem to get the LED probe test to work to check my engine code. Heres my probe.



And here is my engine diagnostic test terminal



Now I've tried everything to get something to light up but nothing ever does. I've taken the probe, grounded it to different points and used the probe end to see if anything light up. Nothing. Is there another connector Im just not seeing? Thanks.

Update:

Took off ECU and was not pleased at what I found.





looks like a fried chip/circuit at D23 on the motherboard, some kind of residue near the cluster of capacitors and a singed black diode on one side at R112. There is also some kind of blue residue near D104
E

I have more pictures that I can put up if you guys need me to. And obviously wont be going anywhere for a while...

How much am I screwed?

Well I'd definitely be looking for another ECU at this point. OR if you cant find one IIRC there is a place down in FL that will rebuild/test your exisiting unit after they replace all defective/leaky components. Cant recall the name or site, but it was mentioned extensively over at the 4x4wire forums for Mitsu's.

You might want to opt for option 2 as anything you get from a yard will have been sitting for awhile exposed to elements, and anything on ebay is just as old as what you have now.

IIRC I think the rebuild cost was $150 or so depending on unit plus return freight costs running anywhere from $10 USPS to $50 overnight if you're desperate.

If you have the time and $, I'd send it out for evaluation and repair while you're digging into other components and doing other testing.

Jim

The link i posted doesnt use a led probe, it uses a mini 12v buzzer which is way easier then using a led light or multimeter, actually read it before just disregarding it.

So i went to a junkyard and found a ecu, but its for a 3.0 . What are the risks using a 3.0 in a 2.4? Running too rich?

Its not going to work, completely different engine.