1990 4WD Mighty Max!

Hey y'all!

Just bought my first Mighty Max off a buddy. I'm told it's a relatively rare one since it has the 3.0 V6 in it! My buddy did a lot of work on it while he had it. He replaced a bunch of seals to fix up the oil leaks, replaced the valve seats, did the timing components and water pump as well as a few other things I'm probably forgetting. Unfortunately it currently has an intermittent misfire, and he just didn't have the time to work on it anymore so I picked it up for a good deal! Got new plugs and wires on order. I'm hoping it will fix the misfire, but if it doesn't where would you fine folks recommend I look next? Happy to see an active community around these old trucks!

Glad I clicked on the photo link COOL LOOKING TRUCK love the chrome hub caps then tires look bigger than stock .

Please Look:
https://youtu.be/4_EFGAFxi1w?feature=shared
https://youtu.be/tGeZQUHzGrg?feature=shared

coil wire to dist cap connection MUST be very snug..!

If misfire continues after doing the above tests THEN (I WOULD) buy a new distributor cap & rotor..

I sprayed electronic cleaner into my distributor then dried with gentle compressed air...

Last might be the gapped IC chip in the distributor...

Must check ignition timing INITIAL VACUUM & CENTRIFIGAL

Good Luck finding the cause of misfire :thumbup:

Thanks Xbox! Appreciate the advice on where to look!

Quote:

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Originally Posted by OR3X

Thanks Xbox! Appreciate the advice on where to look!

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You are more than welcome OR3X please post the outcome to your fix & best of luck.

Welcome to the v6 club. They are awesome.

Quote:

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Originally Posted by xboxrox

Please Look:
https://youtu.be/4_EFGAFxi1w?feature=shared
https://youtu.be/tGeZQUHzGrg?feature=shared

coil wire to dist cap connection MUST be very snug..!

If misfire continues after doing the above tests THEN (I WOULD) buy a new distributor cap & rotor..

I sprayed electronic cleaner into my distributor then dried with gentle compressed air...

Last might be the gapped IC chip in the distributor...

Must check ignition timing INITIAL VACUUM & CENTRIFIGAL

Good Luck finding the cause of misfire :thumbup:

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Ok, so I did a little troubleshooting today.
I was able to determine that cylinder 3 is the one misfiring. I did this my unplugging each plug wire from the dist cap in turn with the engine running. This caused a noticable change in the running characteristic for each cylinder except 3. I also noted that spark would jump from the cap to the wire when I brought it close to the cap. I picked up some spare plug wires from the junk yard because I was too impatient to wait on the ones I ordered. I used on of the spares to replace the wire for cylinder 3 and noted no difference. Next I swapped plugs for cylinder 3 & 5. The misfire stayed at cylinder 3. I then swapped the plugs back and turned over the engine with the original cylinder 3 plug removed. To my dismay it had a strong spark. (No easy fix here) Next I checked the coil resistance. Primary tested at 1.0Ohm and secondary at 12.3k Ohm. From what gathered online, this is a good reading. Next suspect is dist cap and ignition timing? If the plug had good spark when removed from the cylinder is dist cap even worth replacing? As for ignition timing, if it was off wouldn't that result in two cylinders misfiring? Let me know what you think!


I attempted to start a new thread specifically for this issue but it didn't go through for some reason. I'll try again tomorrow and move this discussion to a proper location.

Thanks!

Testing 1 2 3...
For some reason I'm unable to post replies.

Quote:

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Originally Posted by xboxrox

You are more than welcome OR3X please post the outcome to your fix & best of luck.

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Ok, so I've done a bunch of troubleshooting and I tried to post updates a couple times but for some reason it wasn't working. Anyways, here's what I've done so far:

• Identified cylinder 3 as misfiring cylinder by pulling plug wires from dist cap one by one and listening for change in engine
• swapped plug wire on cylinder with used spare - no change
• swapped plugs between cylinder 3 and 5 - misfire stayed at cylinder 3
• pulled plug three and checked spark. - strong spark observed
• tested coil - 1.0Ohm on Primary and 12.3k Ohm on secondary - appears good
• checked injector by listening then unplugging electrical connector and comparing against others - sounds like it's working

I think my next move at this point is to do a compression test on the cylinder and see how it compares to the working ones. There is a quite noticeable tick on that bank of the engine so it could be valve-related. I really want to swap injectors between 3 & 5 to make damn sure it's not an issue with a weak injector or something like that, but just by looking it appears I will need to remove the intake at the very least to get the injectors out. All the plastic and rubber in the engine bay is INCREDIBLY brittle, so I don't want to start taking things apart unless I absolutely have to because I'm certain things are going to start breaking as I take it apart.

Any other ideas?

Quote:

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Originally Posted by xboxrox

Please Look:
https://youtu.be/4_EFGAFxi1w?feature=shared
https://youtu.be/tGeZQUHzGrg?feature=shared

coil wire to dist cap connection MUST be very snug..!

If misfire continues after doing the above tests THEN (I WOULD) buy a new distributor cap & rotor..

I sprayed electronic cleaner into my distributor then dried with gentle compressed air...

Last might be the gapped IC chip in the distributor...

Must check ignition timing INITIAL VACUUM & CENTRIFIGAL

Good Luck finding the cause of misfire :thumbup:

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Quote:

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Originally Posted by xboxrox

You are more than welcome OR3X please post the outcome to your fix & best of luck.

---

Ok, so I've done a bunch of troubleshooting and I tried to post updates a couple times but for some reason it wasn't working. Anyways, here's what I've done so far:

• Identified cylinder 3 as misfiring cylinder by pulling plug wires from dist cap one by one and listening for change in engine
• swapped new (used) plug wire on to cylinder 3 - no change
• pulled cylinder 3 spark plug and tested - observed strong spark
• swapped plugs between cylinders 3 & 5 - misfire stayed at cylinder 3
• tested coil - primary 1.0 Ohm secondary 12.3k Ohm - appears to be good
• checked cylinder 3 injector by listening with screwdriver - sounds like it's firing (metallic tapping sound)
• unplugged cylinder 3 injector and compared with others - metallic tapping noticeably absent

The next thing I want to do is swap injectors between cylinders 3 & 5 to see if the misfire follows injector but it appears that at the very least I will need to remove the intake to get to the injectors. All of the plastic and rubber are very brittle so I don't want to start disassembling things unless it's absolutely certain it needs to be done.

With that in mind I think my actual next step will be to do a compression test and compare between cylinders. There is a noticeable tapping on cylinder 3 side of valve-train so I want to be sure it's not something like a stuck valve before I go chasing injectors that aren't broken.

Let me know what you think!

OR3X

Your replies got stuck in the Moderation queue, not sure why. I went ahead and approved them all, since any one of them may have some useful clue(s) that didn't appear in the others.

Quote:

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If the plug had good spark when removed from the cylinder is dist cap even worth replacing?

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Not quite clear what you mean by "plug had good spark when removed from the cylinder" but your process of elimination does sound like the terminal in the cap for that cylinder might have a crack or other fault.

Could also be a bad fuel injector on that cylinder. Try swapping injectors around and see if the problem follows the suspected-bad injector. If not, could be the wiring to the #3 injector.

Another thing to check would be compression; if #3 is a lot lower than the others, that could be the issue.

Quote:

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Originally Posted by SubGothius

Your replies got stuck in the Moderation queue, not sure why. I went ahead and approved them all, since any one of them may have some useful clue(s) that didn't appear in the others.



Not quite clear what you mean by "plug had good spark when removed from the cylinder" but your process of elimination does sound like the terminal in the cap for that cylinder might have a crack or other fault.

Could also be a bad fuel injector on that cylinder. Try swapping injectors around and see if the problem follows the suspected-bad injector. If not, could be the wiring to the #3 injector.

Another thing to check would be compression; if #3 is a lot lower than the others, that could be the issue.

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Thanks Sub! I thought I was losing my mind! I did a compression test yesterday and the misfiring cylinder only has ~30psi of compression. I don't have any more time to mess with it this week, but I'm going to get the valve cover off next week and see if there's any obvious issues with the valves on that cylinder.

OR3X your truck has the V6 engine, right..?

Adding oil to the cylinder when doing compression test might increase the psi and if so (I think) that means piston rings leak..?!? Maybe a valve is not closing properly, hope it's an easy fix and not a blown head gasket or needs cyl head work... Test the coolant for gas that leaks from bad head gasket, O'Reilly's loans free test kits...

You will fix it oorah ;^)

Quote:

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Originally Posted by xboxrox

OR3X your truck has the V6 engine, right..?

Adding oil to the cylinder when doing compression test might increase the psi and if so (I think) that means piston rings leak..?!? Maybe a valve is not closing properly, hope it's an easy fix and not a blown head gasket or needs cyl head work... Test the coolant for gas that leaks from bad head gasket, O'Reilly's loans free test kits...

You will fix it oorah ;^)

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Correct, it's the V6. I have a friend I race dirt bikes with that happens to be a Toyota master tech. He's going to let me use his fancy leakdown tester this weekend. He mentioned the same trick with the oil in the cylinder to see if it's the rings or not. I think it's worth saving the engine as long as it's anything but cylinder bore/ring damage. If it is I'll start looking for another engine. This truck is just too damn cool to let it die.

Amen newer is not always better $50,000.00 'n up for newer Crap...