Help! Rough idle and die... recent coolant flush

[Mr_Fish]

Hey guys,
I was just on the way home in "Shikoku" ('95 GenII 3.5L DOHC) and am now roadside trying to decipher what's going on.

I drove a total of about 15 miles to destination win no problems. Upon return I made it about 5 miles. I turned the A/C on and off a couple times cause it's kinda warm but not that warm. Maybe the third time that I did so I was stopped at a traffic light and instantly Shikoku went into a very rough, bouncing idle. The engine was unresponsive to the gas pedal and after 8-10 seconds it died.

After a few moments I was able to restart and idly cruise to a gas station. Seemed 100% fine until I rolled to the gas pump and did the exact same thing this time without any instigation from the A/C unit.

Now refuses to start at all. I'm letting it cool down at the moment. Have had zero problems since I swapped the alternator last fall sometime and the only recent thing I can think of was a coolant flush I performed last weekend. I recklessly spilled a lot of 50/50 when removing the thermostat. Definitely soaked my belt assembly but didn't appear to get into the alternator much.

Currently, oil levels good, no milk. Coolant level seems to be good though my flush last weekend did strangely result in less coolant going into the system than the ~10qt capacity. Temperature gauge is reading normal. I have an OBDII scanner on the vehicle but can't get a code read out for some reason.

Any ideas?



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[PacS14]

Maybe air in the system? Although that would only make your engine run hot. Test the alternator and battery. And pull a spark plug wire one at the time to see which one is malfunctioning.

 

[Mr_Fish]

Thanks I'm guessing it's the alternator. Battery is fine for now. It cranks and fires but won't run. It wasn't overheating at least by the dash gauge and I never received a check engine light so I'm guessing it may not be a sensor. The rails are getting fuel but I'm not sure how much pressure is on the line.


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[freewayross]

Did coolant get into plugs? Checked the fuel pump?How many miles on the truck?

 

[RyanY]

If it's cranking the engine normally then the battery should have enough power to run the engine as well, even if the alternator isn't working. What is your voltmeter showing?

 

[Mr_Fish]

Did coolant get into plugs? Checked the fuel pump?How many miles on the truck?

I don't think coolant got into the plugs as my spill was only on the pulley assembly at the front of the engine. Unless I'm missing something I'm not sure how the coolant could have worked its way back to the plugs especially on the 3.5 engine.

Fuel pump seems to be fine. I unhooked the fuel supply line and gave the engine a short crank to ensure fuel was making it to the rails.

I'm at 170k right now.


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[Mr_Fish]

If it's cranking the engine normally then the battery should have enough power to run the engine as well, even if the alternator isn't working. What is your voltmeter showing?

Well that's not encouraging I was under the impression that only the alternator fires the spark plugs on this engine.

The voltmeter is reading normal (~12v) but the needle is a little sluggish to show the full reading when I turn the ignition on.


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[freewayross]

I don't think coolant got into the plugs as my spill was only on the pulley assembly at the front of the engine. Unless I'm missing something I'm not sure how the coolant could have worked its way back to the plugs especially on the 3.5 engine.

Fuel pump seems to be fine. I unhooked the fuel supply line and gave the engine a short crank to ensure fuel was making it to the rails.

I'm at 170k right now.


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It can creep in if liquid spills on valve cover, few weeks back a friend detailed his LS 400 (V8) engine bay and the car started misfiring (culprit: water in plugs)

Back to topic: Did you check spark/ spark plugs? How old are the plugs and wires?

 

[Mr_Fish]

It can creep in if liquid spills on valve cover, few weeks back a friend detailed his LS 400 (V8) engine bay and the car started misfiring (culprit: water in plugs)

Back to topic: Did you check spark/ spark plugs? How old are the plugs and wires?

No coolant got anywhere on the valve cover that I could tell. I haven't gotten into the plugs and wires since I've owned it (1.5 years). I've heard it's pretty involved to swap them and that the standard ngks are long life plugs.

I got DTC codes 13 and 25 with the paper clip trick in the OBDII port. I thought 13 and 25 were intake air temperature sensor and barometric pressure sensor respectively but I swapped both this evening with no luck. Guess it could be a bad harness connection.

I'm trying the camshaft sensor tomorrow and if that doesn't work I'll be looking into the plugs and testing the rest of the sensors. I'm leaning away from the alternator but hoping it's not a timing issue though not sure how it could've been thrown off.


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[jaccox23]

Maybe check your ground connections. Not sure if the DOHC has the same grounds on the AC bracket as the SOHC but it'd be a quick check just to be sure.

 

[Mr_Fish]

Thanks, I'm going to attempt to check all the grounds and sensor connections to the ECM this morning while I wait on the new camshaft position sensor to arrive.

So far, I've checked: fuel- I unhooked the main fuel supply line right before the rails and cranked the ignition for a second and definitely had fuel spray out so I'm assuming the injectors are getting fuel to the cylinders; Fire- voltmeter is reading normal and when I crank the ignition the vehicle fires and turns over but dies immediately so it seems I'm getting spark at the plugs.

Next steps- 1. checking sensors, grounds and inputs to the ECM, 2. install new camshaft sensor, 3. Fuel Pump/Filter? Alternator? Timing Belt? I don't know maybe the fuel pump/filter isn't getting enough pressure on the line to push it through the injectors.

Any advice greatly appreciated from the crew here.

 

[RyanY]

Testing parts before you replace them is a far cheaper way to determine if they are actually the cause of your problem.

 

[Mr_Fish]

Testing parts before you replace them is a far cheaper way to determine if they are actually the cause of your problem.

'Preciate it brother. I received error codes on the two parts that I've replaced and that was the purpose in doing so preliminarily.

Spent today testing the MFI inputs and harness connections. Nothing amiss so far. Planning to get into the plugs/ignition system next.

Any other ideas on this thing?


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[montero98ls]

Have you checked your IAC?

 

[normal_dave]

The Ignition Control Module was my big no start mystery several years back, didn't think your '95 had one or I would have responded sooner. Take out your multitester, since you are waiting on parts and run the test in the link in this post, #8:
http://www.expeditionportal.com/forum/threads/159696-Replacing-Gen-3-Heads-(Like-a-Virgin)-Any-Recommendation?p=2110222#post2110222

Here was another ignition surprise about the 3.5L, the fact that cylinders fire in pairs, only the one not needed fires on the exhaust stroke, so lets check coil packs.
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From a Justanswer post:
Mitsubishi 6G72 Timing Events

Cylinder numbering and arrangement
The 6G72 is a 60º V6 gasoline engine that displaces 2.972 liters. The cylinders are arranged and numbered as shown below.
Mitsubishi 6G72 cylinder numbers
Ignition Timing
The firing order is 1-2-3-4-5-6, with each numerically-successive cylinder reaching top dead center (TDC) 120 crankshaft degrees after the previous one. Paired cylinders have pistons at the same relative position, such as both at TDC, but they are 360º out of phase, such as one is in the exhaust stroke and the other is in the compression stroke. Paired cylinders are 1-4, 2-5, and 3-6. Spark plugs are fired simultaneously in paired cylinders, during the compression stroke for one cylinder and during the exhaust stroke for the other cylinder. The spark during the exhaust stroke is wasted because the basically inert exhaust gas cannot combust.
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At least another item to eliminate...