Acted funny, now turns but no start, help!

[Lanklo]

'90 MM 2.4l. 89k. Replaced a warped head, set base timing & run timing. All seemed to be going well. After some runtime and checking other items the motor seemed to be harder (slower) to turnover and get started. Weak battery ✔. Had to give alot of throttle to get started and it would rev high & low. Maybe I didn't tighten distributor ✔ timing seemed way off like 30ATDC.
Cursory checks I did 1) cam gear at mark, crank at 0 & rotor pointed at 1 ✔. Pulled codes 13 ( air intake sensor) & 25 ( BARO sensor) ahhh MAF, power & ground ✔. Disconnect battery to reset program, unplugged MAF to get original signal ✔. Still not trying to catch at all. Spark to plugs ✔ Strong fuel flow at high pressure hose ✔ When starting last time prior to no start it acted like one or two cylinder s were stumbling, then it caught and revs went high and low then back to acouple of stumbles and just shutoff. Has not and doesn't try to start since.
I know I am rambling but am frustrated. Middle of a complete home remodel and need my baby running.
Suggestions, thanks.

[geezer101]

Check all of your ground leads. Bad grounds can cause weird issues. Second, check the starter motor. It could be due for a clean out and freshen up. Intermittent misfire or poor spark is hard to diagnose. May be a weak coil...?

[Lanklo]

Going to check coil since it didn't have a bright spark. Will check grounds also.
Thanks

[Lanklo]

Hopefully, resistance on maf sesor seems all over the place. Replacing tomorrow.

[finalfighter]

check the ecm. caps could have gone bad.

[geezer101]

check the ecm. caps could have gone bad.


+1 on that recommendation. The ECM's are known to go bad, it will either throw the engine into limp home mode or not run at all. You will be looking for swollen capacitors on the ECM board and/or signs of staining on the circuit board. If you can read the capacitor values and wield a soldering iron this is in the realm of a DIY fix. Also observe any dry or crap looking soldered joints and retouch them while you have it apart.

*addendum - the 1990 model truck has a year specific ECM and sensor set up. Not easy to track down certain parts (think it is the MAF sensor...) and other year model ancillaries are not compatible.

[Lanklo]

Thanks for all the advice. MAF suppose to have 2.5k ohm @68 degree. Mine came in at 2.51k. Is this enough difference to cause a no start?
Thanks for all info from everyone.

[Lanklo]

That is it should read 2.7ohm but is at 2.51ohm...

[Lanklo]

You're rigjt geezer101. Pulled ecm and there are two burnt capacitors. Was already a remanufactured in it and ready for third unit at 89k + 31yrs.

[geezer101]

Not surprised but it's still a PITA. The 1990 ECU and ancillaries are year specific which makes this one year run model a biatch to work with if you aren't in the know. The roasted capacitors will set off false error codes which turns ECU code diagnostics a gremlin hunt. As long as the board isn't damaged you can swap out capacitors (you can run bridges across the board if a trace has taken a hit) Be careful of the type of replacement cap you use as some may have the same microfarad rating but don't play well with ECU's. There are threads here on what caps are recommended and a general run down on how to do it. The factory electrolytic caps in the Max' ECUs are used due to their low noise feature but they leak from age and heat cycle exposures. And use lead solder for the joints and not the tree hugging lead free garbage. This might be helpful-

https://docplayer.net/41544408-Rebuilding-mitsubishi-ecu-ecms.html

[geezer101]

...and give cred to finalfighter - he suggested it first ;)