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2G What's my problem?

waltah

Proven Member
94
32
Mar 2, 2011
fairfield, Virginia
'95 GST, auto, 150k miles but engine probably less, bought about a month ago, runs very well except when you get to about 7 psi boost in any gear there's a groaning noise and loss of power. Boost does not fall -- it'll go right on up to 15 psi.

Could be a very regular miss -- I've never had a waste spark car before so I don't know what a single coil failure under load might sound like. I did swap the transistor assembly -- made no difference. Doesn't seem likely to be a mixture problem -- it's too smooth and regular, also the plugs look fine and gaps are correct. I wonder about a clutch chattering in the transmission but what clutch would be in action in all gears? Also, clutch problems I've seen have all been totally silent slippage but those were all on the smaller transmissions.

Additional symptom, possibly related: There's an occasional single or double 'thunk' miss when I come to a stop light. Sometimes doesn't happen at all, sometimes happens a few times before the light goes green.

If possibly a coil failure is there a way to swap coil packs without removing the fuel rail? Manual says 'unbolt transistor and take out, unbolt coil pack and take out' and that's it. But my car has the Diamond F648 assembly and I couldn't figure out how to get it out of there without removing the rail. Hopefully I'm missing something obvious ???
 

waltah

Proven Member
94
32
Mar 2, 2011
fairfield, Virginia
I exchanged the coil pack. It made no difference. Spark plug gaps are within tolerance. I don't think this is an ignition miss and it's too regular to be the usual sort of fuel/air problem. Could possibly be a partly blocked injector and since the car never starts on the 1st/2nd revolution if it has set for a few hours but stumbles to life it's likely there's some sort of very slow leak -- but no trace of a fuel smell after a drive. This could be a slightly leaky injector and eventually I'll replace them. E10 is terrible for cars with aluminum parts in the fuel supply -- the injector rail -- unless they're driven quite regularly. This one sat most of the last year and probably quite a bit before that.

Consistent with a partly blocked injector both Low and Medium fuel trims are about +4% indicating the ECU thinks its running lean. So a bad injector could be the cause of the shudder.

However I'm going to try to eliminate a transmission shudder first. After trying it a few more times (only happens at about 10 psi boost) I think that:

1. It's not a loud enough sound to be picked up by a cell phone -- you feel it rather than hear it. And,
2. If in the transmission it's most likely 'torque converter shudder' caused by repetitive slipping a bit when trying to lock up. This condition is discussed on the web for just about every car that has a lock-up torque converter though I haven't seen it mentioned for 1G or 2G DSM.

I've already done the first corrective step -- changed the fluid, putting in Mitsubishi SP III. This was an obvious step anyhow because I have a service record from a year ago when five quarts of very cheap fluid was put in.

Just a couple of days ago I added some stuff that's supposed to fix torque converter shudder and has excellent reviews -- 800 some and a 4.7 score on Amazon. It didn't give an instant fix but the shifts are more positive. Many reviewers said it took a while to work but If after 100 miles or so the shudder is still there I'll take off the pan and replace the filter, changing the fluid again.

I've bought four used automatic Mitsus over 25 years. Not one of the three that had enough miles to need a fluid change came with the right fluid in it. All required multiple changes with driving a few days in between to start shifting properly. $#@)#!!

Anyone ever had torque converter shudder in a 2g automatic? Or is this so rare that I'm likely barking up the wrong tree?
 

waltah

Proven Member
94
32
Mar 2, 2011
fairfield, Virginia
No resolution yet but enough water over the dam to justify an update. I think torque converter shudder can be eliminated since the diagnostic procedure for this (disconnect the trans fluid temp sensor and see if the problem goes away) changed nothing and the next step in the procedure is 'figure out what's wrong with your engine.'

Strongly suspecting I had a leaking injector (the 'stumbles to life' after sitting overnight, also no pressure and little fuel in the rail if the pressure regulator is removed before starting in the AM but NO smell of gas) I swapped in a set of used injectors. That eliminated the symptoms of 'leaky' but made no difference to the miss under boost or the occasional single miss at idle when closed loop but not fully warm.

Swapping in the ECU from the (new) parts car mainly to test it made no change at all.

A miss under load is often a high voltage problem; I swapped coil packs, no change. I re-gapped the plugs from about 0.031" to the minimum -- 0.028" -- and that seems to have raised the amount of boost required to produce the miss from 8-10" to 12" or so. So there's a good chance this is a high voltage failure. I cannot see anything wrong with the wires and the resistances check okay but I've had wires look and test okay in other cars and a miss under power went away with new wires so they are now on order.

There are wires on the parts car but they look like something left by the dog behind the sofa ... might be worth swapping for the heck of it I guess.

And a new symptom: The idle RPM is sometimes okay -- obviously being controlled by the ISC -- and sometimes not -- wandering around 1200 and dips when headlights turned on. A not-quite=right adjustment of the throttle position switch? Car has 150k, so everything in TB is a bit worn.

This goes slowly because the fix-it list is 57 items and I just work on what's convenient whenever I can. Plus everything takes a lot longer than it should because this is my first Eclipse and there's lots of Mechanic Inefficiency.

Most of it wouldn't interest anyone here -- 10-20 hours work on the scavenger hunt for bumper assembly parts, (front & rear were '98, I'm returning to '95 per the actual car) straightening, welding, painting bits of tin, finding the right bolts and push fasteners ... the parts car front was worse than my 'driver.' Three hours replacing bulbs and swapping the 'parts' instrument cluster -- original lacked an indicator for 'low coolant' though the bottle has the switch and the wiring is there all the way to the cluster. I still have to swap the speedometer assembly back 'cause the parts unit trip odometer is messed up.

And of course every item is actually a bunch of items: You think when I put the idler and belt back on that the A/C will spit cold air? This generation has no cabin air filter so at least the evaporator has to come out, meaning recharge ... maybe there won't be any leaks?

Maybe. And lots more like that ... My goal is to fake a well-maintained and mostly original one owner '95 GST. Maybe in a year or so.
 

waltah

Proven Member
94
32
Mar 2, 2011
fairfield, Virginia
Ta-DA! It was the spark plug wires. After replacing them I was able to push the boost to around 15 psi without a problem. In the next day or two I'm going to take the bad wires and go over them very closely looking for the problem just for education.

The increase of torque falls off pretty fast above 11 or so psi but I'm running stock injectors so there's likely not enough fuel above there. Not really a problem -- I don't plan to use that higher power anyhow -- just don't want any failures that would likely get worse over time. I will look at the fuel pump and strainer and unless it looks new, replace the filter.

The trick of reducing the gap of spark plugs -- even to less than spec -- in order to lower the maximum voltages in the HV system to see if that makes a problem better is handy for for confirming that it is a problem there and not somewhere else -- bad injector or whatever. I should have done that earlier.

So much for that. There's a rattle that sounds like it's in the left quarter or trunk that's driving me nuts. How hard can that be?
 

waltah

Proven Member
94
32
Mar 2, 2011
fairfield, Virginia
Before throwing those bad spark plug wires in the trash I looked them over very closely. Two I couldn't see anything. One, however had a slight shiny spot where it had (evidently) been rubbing on a valve cover bolt down there in the valley. in the middle of the shiny spot was the tiniest black dot and an inch or so of that part of the wire was very slightly darkened.

And another wire showed just the tiniest dot.

These were OE 7mm wires, quite possibly those that came on the car.

Of course none of that is supposed to happen: The 4g63 engines came with five plastic wire separators that keep the wires not just in the right order so there won't be crossfires caused by induction between wires but also to keep them from touching anything metal or even each other. These often seem to be gone in older cars -- none of my 90's Mitsu's had a full set but they actually do have a function and I wish they were easy to buy somewhere. I got one of each from Mitsubishi a couple months back but the other two (duplicates of one I got) seem to be unobtanium.

Not to worry: I will make them when I get a suitable chunk of plastic.

The other way to go is better insulated wires -- 8mm, 10mm, whatever. Additional line of defense, gap the plugs to the minimum recommendation -- 0.028" I believe for the 4g63t, more on the NA engines -- to minimize the high voltage.

A trick I should have tried once I began to suspect a high voltage failure: Go out on a dark night and watch the engine run with no light at all. It could be that the spark wouldn't be enough to see (maybe behind the wire or whatever and there was no obvious problem when idling anyway) but it would have been easy to do and would have fingered the trouble very quickly if it succeeded.

The left quarter rattle was the left rear seatbelt upper mounting. Fastening the seatbelt and pulling everything up made it go away.
 
Last edited:

motomattx

Proven Member
3,490
1,322
Dec 9, 2010
wampum, Pennsylvania
Actually even in a car with perfectly good wires its not unusual on a dark night to see sparks emanating from the wires, there is a corona that comes from them that can be normal.
 

BLACK'98DSM

Proven Member
3,292
1,133
Feb 9, 2019
Alabama
I remember grabbing a spark plug wire to move it away from a manifold and zap… All I could see is little white dots, and it set me on my butt. I could not believe how much power goes through those wires. Never do that again.
I've done the exact same thing on my Eclipse LOL . I made a thread about it at some point
 

luv2rallye

DSM Wiseman
8,081
935
Jun 7, 2003
Minneapolis, Minnesota
For not starting right away did you rule out a bad/weak fuel pump or leaky FPR? Fuel pressure should be maintained for hours and even days after engine is turned off. Measure fuel pressure while engine is both on and off for hours if suspect.
 

waltah

Proven Member
94
32
Mar 2, 2011
fairfield, Virginia
On those old wires do an ohms reading and see if there is a difference between them... Just out of curiosity...
I did that early on, though I don't remember mentioning it. Each was a few thousand ohms end-to-end in proportion to length as you'd expect.

I have had wires fail where the connector at the end was no longer actually hooked to the wire or where it pushed back up into the spark plug shield (whatever they call those things) far enough to not really engage the top of the plug so there was a bit of a gap there --- it would be okay for idle/light loads but crap out when pulling due to higher voltage being needed at the plug.

For not starting right away did you rule out a bad/weak fuel pump or leaky FPR? Fuel pressure should be maintained for hours and even days after engine is turned off. Measure fuel pressure while engine is both on and off for hours if suspect.
I did. And you're right -- if there isn't pressure in the rail the next day then there's a leak. Either you can smell it -- I've had a pinhole in a fuel pressure hose and a leaky flare nut fitting on the Expo's -- or it's an injector (leaking into the intake manifold) and changing that injector fixes it. This time it was the #2 as I recall. Came with the car, which had been sitting most of the time for several years.

I was surprised to discover that you can buy gaskets for flare nut fittings -- sort of a dished copper washer you put in there. Only needed when the fitting has been overtightened so the threads bottom without sealing the flare but on old cars worked on by ?? people, sometimes ...

Pumps I just don't know ... what kind of pumps are these, anyway? I've been wanting to cut one open and look but not yet gotten around to it. One can imagine the pump leaking back into the tank but I've not yet seen that happen.

Anyway the car runs like a top now, after injector and spark plug wire replacement. The idle speed is a little unreliable -- sometimes clearly being controlled by the ISC and sometimes faster -- maybe 1200 or so even when warm. Before digging into the ISC I'm going to replace the seals on the injectors -- up to now I've just used whatever was on the old injector even if it felt like 26 years old rubber so air leaks there are a possibility.

I try to go a step at a time because 'mistakes happen' and fixing things that aren't clearly the problem I'm worried about sometimes breaks something else.
Actually even in a car with perfectly good wires its not unusual on a dark night to see sparks emanating from the wires, there is a corona that comes from them that can be normal.
Yeah, important distinction between corona which will be sort of a blue violet fog along a wire and is normal and a spark which will be at a point (or points) and is a failure.

I expect most of us have grabbed a spark plug wire -- once. ;-)
 
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