420A hiccup 420a engine

[techboj]

Currently have two eclipse(s). A 99 GSX with the Mitsu 4g63 engine and a 97 RS with the 420a engine. For the most part, the 420 car is stock and unmodded but has recently developed a somewhat intermittent hiccup. It starts well, idles fine (both with AC off or on) but on rare occasions, I would get a "hiccup" almost like the gas supply has been interrupted or the ignition cuts off momentarily (split second). This does not happen at high speeds (50 kph and above) and it almost always happens within the first 2-5 minutes of driving off. With the engine cold (parked overnight), start the car and within that 5 minute time frame, I would notice that hiccup or misfire. With the engine warm (driven a certain distance, then parked for a few minutes), it is still possible to get that hiccup within the first 1-2 kms. So cold or warm engine doesn't matter.

Plugs have recently been changed and properly gapped (less than 2 months ago) - but the problem existed even before the plugs were replaced
Fuel filter - near / underneath gas tank has been replaced (about 6 months ago)
No bad gas / stale gas -also gone through a cycle of premium and injector cleaner

Cam position sensor has been replaced by non-oem a few years ago - although the reason for replacement was that the original was damaged/hit and broken - it did not fail electronically - only the plug/connector was damaged
coil and spark plug wires are still original

The fuel pump relay (one of the three relays near the firewall/brake reservoir) was previously replaced as it has gone bad before but that actually caused the car to just die while driving. Obviously the fuel pump would lose power when the relay was failing. After it was replaced (a few years ago), the car has not had any symptoms that affected drive ability - until now

No engine related CEL

Again, the symptoms are fairly intermittent. Maybe 1 in 10 or even 20 times of using the car. It would feel like either the engine will hiccup because of an electrical or gas related issue - and it would only happen within the first km or 2 after driving off never at WOT

So question remains - what could possibly be the cause or has anyone had any similar symptoms with this engine? any help or suggestion would be appreciated

 

[dustyboner]

mine did that for a while. but i ended up pulling the motor, freshened up everything except the rotating assembly. and when i reassembled the motor i replaced most of the sensors cause it was easier than cleaning the old ones.

i know it wasn't the coil cause i tried 4 or 5 different ones. wasn't plugs or wires. or IAT, ECT, MAP or CAM sensor. im sure i tried a few differnt sets of injectors too.
EGR was blocked off, no evap, im sure i tried a few different throttle bodies w/sensors, so it wouldn't have been the TPS or IAC

i guess it could have been the crank sensor
or i had a tiny exhaust leak right after the front o2 (greddy header, flange after collector) but the sensor was new for sure, cause i ended up with a bunch of new ones and i used to change them after like 10k maybe less.

When i pulled the head there was horrible carbon build up on everything
i figured that was what was causing the hiccup.

can't say for sure.

 

[BLACK'98DSM]

Do you have a way to view live data?

 

[techboj]

Do you have a way to view live data?

Not at the moment. All i have with me is a cheap OBD2 reader that doesn't do live data. I will try and go to a shop and see what they have to say when I have time. Thanks.

 

[techboj]

Update on the hiccup issue - hopefully somebody might be able to chime in with some insights and their personal experience...

From the random "hiccups" , I was driving the car around and it suddenly died. Almost like the ignition cut out. Pulled to the side and tried restaring the car. Nothing. Stepped out of the car, opened the hood and I could hear a faint "whistling" sound (almost like a weak high pitched continuous beep) coming from the ECU. I quickly unplugged the top connector of the ECU briefly and the whistling went away. Replugged it and the car started fine and I was able to return home without further issues.

A few days later I felt I was experiencing random misfires. A quick check with my cheap portable OBD2- confirmed P0300-304 codes. So now my attention got directed to the spark plug wires and coil (since both were still Orig OEM). Plug wires were replaced with Denso and the Coil was replaced with an Ultrapower (looks like an Accel OEM - since it shares the same color and part number). Regardless, the roughness from the misfire went away after that but for some reason, I could NOT delete the code using my OBD. It just kept saying erase fail.
So I went to a trusted and reputable shop near me and the owner / head mechanic hooked up his pro OBD2 scanner and aside from the existing codes (P0300-0304), he said he could not see anything unusual with other readings. The only "quirk" he mentioned was that it took far too long to reset the ECU. While most would take a few seconds to a minute to clear, he said that it actually took almost 5 minutes.

Drove the car after that and seems ok. Been checking if codes will return or if any new codes will come out. Nothing. Then finally a few days ago, the car died as soon as I was pulling out of my driveway. It was the same situation. The car felt like it choked on air or gas (or lack of) and then died. Again, opened the hood and heard the faint whistling from the ECU. Quick unplug and replug and the car restarted normally albeit with a little bit more smoke than normal from the tailpipe. I drove the car to the end of my block and the smoke was gone by the time I returned to my driveway. Now, I'm thinking that with that smoke, the car could have run momentarily rich. Also has anybody experienced the "whistling" from the ECU or is it a sign that it might need replacement?

 

[BLACK'98DSM]

I couldn't imagine a reason why the ecu would have a whistling noise coming from it... there are no moving parts inside it. There's a 1/2" deep layer of Chrysler gel coating the circuit boards. Are you sure this noise was not coming from a radiator fan? I know it would seem obvious whether it were the fan or not, but there's no way the noise was coming from the ecu. Unless for some reason your ecu has a cooling fan in it?

 

[techboj]

I couldn't imagine a reason why the ecu would have a whistling noise coming from it... there are no moving parts inside it. There's a 1/2" deep layer of Chrysler gel coating the circuit boards. Are you sure this noise was not coming from a radiator fan? I know it would seem obvious whether it were the fan or not, but there's no way the noise was coming from the ecu. Unless for some reason your ecu has a cooling fan in it?

I'm surprised as well.

Yes. I'm pretty sure it's the ECU. It's a very faint high pitched continuous sound - but is truly electronic and not mechanical in nature around 6000-6500Hz which immediately goes away as soon as I unplug the top connector of the ECU. I'm not sure if I can capture it with my mobile phone mic but I've shown it to a 2 people and both confirmed hearing it from the ECU box. It only happens when the car cuts off / dies and the sound doesn't go away even with the engine off and nothing else is running. So it can't be a vacuum leak of some sort because it doesn't waver in frequency nor does it go away or stop. The only way to stop it is to unplug the top ecu harness or turn the ignition off after the car has stalled.
And yes, I know that the ECU components are covered with gel inside, I opened it just to see what was inside back in 2007. Which is why that sound puzzles me.

I will detach the ECU from it's mount and then try and see if I can replicate the squealing/high pitched sound when it occurs. Hopefully, somebody else might chime in with a similar experience.

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[1999RSfwd]

A faint high pitched continuous sound is a better way to describe it, than "whistling". My 420a ecu does the same thing. Eventually the sound will go away, if you listen long enough.
I always assumed either some capacitors, or something else on the circuit board was going bad. And as you can see, the ecu wasn't meant to be serviced, because of the potting compound they used. I guess if you had a spare ecu, you could try and remove the potting compound, but it would probably be hard to not damage anything.

 

[BLACK'98DSM]

If you had a spare ecu you should just run that one instead. The prices of these ecu's are pretty cheap anyway, especially at junkyards.

 

[techboj]

A faint high pitched continuous sound is a better way to describe it, than "whistling". My 420a ecu does the same thing. Eventually the sound will go away, if you listen long enough.
I always assumed either some capacitors, or something else on the circuit board was going bad. And as you can see, the ecu wasn't meant to be serviced, because of the potting compound they used. I guess if you had a spare ecu, you could try and remove the potting compound, but it would probably be hard to not damage anything.

Yes. Thank you ! That confirms my suspicion regarding the sound coming from the ECU and that I was just not "hearing things" . Did you eventually replace the ECU or have you continued to run the old ECU without any problems? I will try and see if I can find one locally with the same part number. I understand the 97s, 98s are different and there are small differences even within the same year. Mine is 3013AC but I've seen a 3014AC as well for the same model year.

 

[BLACK'98DSM]

The only main differences in the ecu's for 2g Eclipses is for the evap system and for the cruise control. Cars without cruise control had a different ecu, and the evap system is different for 2ga and 2gb and again in '99.