Idling Hiccup/Intermittent Stumble, Diagnosis?

[Ski Bum]

I was hoping that some of you Mitsu gurus could help me diagnose an intermittent idling hiccup my GSX has. The hiccup is intermittently present at any rpm level while in neutral, I have not noticed any surging or power loss while driving.

First I suppose I should list what I have already replaced/fixed and we can go from there. My profile has my current mods as well.

- NGK BPR7ES, gapped to .028" (could they be too cold)
- New Accel 8mm wires
- Cleaned throttle body
- Vaccum/boost leak test (replaced gaskets, no longer leaks)
- Timing belt, balance belt and all drive belts
- Timing Belt Idler Pulley
- Timing Belt Tenshioner Pulley
- Timing Belt Hydraulic Tenshioner
- Balance Shaft Belt Tenshioner Pulley
- Water pump
- Oil change mobil one and factory filter (alot smaller than fram that was repalced?)
- new Oil cap
- New BISS screw and o ring
- new Thermostat (160*)
- new Radiator cap
- flushed coolant and replaced
- new fuel filter
- new o2 sensor
- refurbished ECU (motoguys garage from ebay)

Hopefully I didnt leave anything out. Along with that I have adjusted the base timing to 5 degrees advance and set the idle the best I could to 800rpms.

The car passed smog with flying colors and was actually very clean, below average in 2 of 3 categories, even here in California.

Possible problem areas:

- The car has a catylitic converter which could be clogged? Not sure about that, am planning on replacing with straight pipe.

- There is a slight exhaust leak between the turbo exhaust port flange and o2 housing flange.

- Upon inspection of the plugs there is carbon fouling on the lower half of the plug (on the threads, not the tip). Along with the carbon fouling on the plugs a black liquid sputters out of the exhaust tip. I dont have an AFR gauge but my hunch is that I'm running rich. Could the hiccup I'm hearing be the rich exhaust reigniting within the exhaust system?

Aside from that is there anything I have missed?

 

[PhazinBlack92RT]

I also have been having this same issue. I hope to get resolved with my AWD keep us posted.

 

[andymoraitis]

I then performed a quick compression test and then depression set in. Cylinder 4 130, cylinder 3 120, cylinder 2 110, cylinder 1 120. Something is wrong. I ran a compression test a month ago and got 152 from every cylinder, textbook.

I can understand your frustration, but before pulling things apart, I'd recommend re-doing the compression test. Ensure that the motor is up to operating temp, pull one plug at a time to test and make sure the throttle plate is wide open. If you get similar readings, perform a wet test on all cylinders by dropping a capful of oil in prior to testing. If the compression goes up, it could be a ring seal issue.

Get back to us and hang in there,

Andy

 

[Ski Bum]

I can understand your frustration, but before pulling things apart, I'd recommend re-doing the compression test. Ensure that the motor is up to operating temp, pull one plug at a time to test and make sure the throttle plate is wide open. If you get similar readings, perform a wet test on all cylinders by dropping a capful of oil in prior to testing. If the compression goes up, it could be a ring seal issue.

Get back to us and hang in there,

Andy

Now I'm really confused.

I start the car up today to bring up to operating temp for the compression tests. To my amazement it starts right up idles up to 1800rpms and sits there idling smoothly, all four cylinders firing. WTF I let it idle down naturally to 900 rpms and it sits there like nothing happened last night. Now I'm thinking this may be ECU/electrical related. I went ahead and performed the dry and wet compression tests. Here are the results:

cyl - PSI dry - PSI wet

4 - 131 - 155
3 - 121 - 151
2 - 125 - 155
1 - 120 - 145

So cylinders 3 and 1 are at the factory service limit while 2 and 4 are just low and all seem to show that I have ring seal issues according to andymoraitis.

I'm worried now that the saem thing will happen as last night if I drive the car now. Why would last nights episode not repeat itself every time the engine runs now?

*EDIT* I drove the car to work today and it seemed ok. I however did not go over 4k rpm's, too nervous. I may begin saving for new upper end parts or a SBR remanufactured head which will give me a little upgrade as well. I'd rather take the precautious road and plan to replace the head parts before something serious actually happens.

 

[andymoraitis]

I know you have to be frustrated by now and while you very well may have ECU or electrical problems, the biggest issue is that the wet test shows that you need to dig into the motor. When compression rises that much from dropping a capful of oil in each cylinder, you've clearly got leakdown problems.

I wish I had better news for you. Perhaps someone else with experience can confirm if they drive on compression this low, but unless someone does, I'd consider a rebuild at this point and not drive it.

Andy

 

[Ski Bum]

I know you have to be frustrated by now and while you very well may have ECU or electrical problems, the biggest issue is that the wet test shows that you need to dig into the motor. When compression rises that much from dropping a capful of oil in each cylinder, you've clearly got leakdown problems.

I wish I had better news for you. Perhaps someone else with experience can confirm if they drive on compression this low, but unless someone does, I'd consider a rebuild at this point and not drive it.

Andy

As frustrated as I am I am not all that upset about the notion of a rebuild. My original goal was to wring 300whp out of this car and doing it with a motor with confirmed internals would make me feel alot more confident that its going to last.

I do have an extra 4G63T sitting in my garage, although its condition is questionable. I suppose I could always pull the top end off and have a peek inside at how things look and decide if that would be a good source for replacement parts. If not, like I mentioned before I would be interested in the SBR remanufacture head. Along with that I figured some cams, like the FP1's or 264's along with some ARP head studs would finish off the top end nicely. As far as the bottom end goes, what options do I have using the stock pistons, rods, etc? Can I simply repalce the pston rings and leave it or is it more involved then that?

Thanks again for all the help!

 

[doggo]

I just bought these seals, CR #3930 from Kaman at the local office here in Columbus Ohio for $4.90 ea.

Update- Seals put in- WHAT an IMPROVEMENT. Major boost leak eliminated

 

[Ski Bum]

The last two days I have been driving the car, very carefully, not reving past 4k and certainly staying off boost as much as possible. Today. I was at the Mitsu dealership getting a new key made, which dint work out anyways and as I was leaving the car began sputtering like it did a couple nights ago (see post on 01-23-2006 10:26 PM). Along with the sputtering and running on 2-3 cylinders at time the check engine light came on, which didnt come on the last ime this happened. I managed to get the back into the dealership where after talking with the service writer for 30 minutes or so about everything that the car has done and all that I have done too it, I decided to just leave it with them so they can run a diagnosis and pinpoint what is causing the problem. Unfortuantely the base fee for that is $130 but if they can tell me exactly what is wrong and save me the trouble and time finding it on my own then I would feel its worth it. Hopefully I should get an answer by tomorrow.

On a good note, while the car is at the shop they're going to replace the seal in the transfer case and replace the u-joint under warranty.

 

[I_eat_DSM's]

Bwahahaha least you get some warranty work done....

Let us know what they say!

 

[Ski Bum]

Got the car back today, the transfer case should be good to go. As far as the engine problem, it turns out that the code was a P 41 (injector), which was a bad connector on the #3 cylinder injector. They replaced it and it ran fine after that. The dealership didnt end up charging me the full fee which was cool of them.

So, no more cylinder shutting down but.... My idle still sucks! I think the next thing will be to replace the ISC and see if that does the trick.

 

[I_eat_DSM's]

If you have a Haynes or a Chilton's it is very easy to check and see if you ISC is good. (they're freakin expensive!) I'd also check your base timing, and how much vacuum do you pull at idle now?


My AIM S/N is in my profile, catch me on AIM sometime and we'll chat and hopefully get this sorted out.

 

[Ski Bum]

I have both so if we get some clear weather I'll look through the books tomorrow and run the tests.

The base timing is dead on 5* advance

As far as the vacuum goes, at 900rpms (when the idle is the most stable) my gauge reads between 14-15 in/hg and while engine breaking it peaks at around 23-24 in/hg.

Also the EGT I just installed reads 940-1000* at idle and 1250* when driving easy and up to 1350* during hard driving.

*Edit I my EGT hit 1400* today while cruising at 4k rpms for a few minutes.

 

[Ski Bum]

While the car was at the dealership the other day, I had an interesting talk with the service writer about the car and what I had done to it. I expalined that the engine lost about 20-25 psi of compression per cylinder. The first thing he asked me was, "Is there oil in it?", duh! but a good question nonetheless. I told him I had just changed the oil and filter with Mobil One synthetic. He then asked me if the previous oil was synthetic. I didnt know as the previous owner didnt know either He told me that if it was regular oil before then I could have actually hurt the engine by putting in synthetic at this point. I havent read anything to back this up but he said that all of the synthetic conditioners in mobil one (and other synthetics apparently) could have dissolved the "gunk" and "stuff" helping the rings seal the cylinders. He said that might explain why the compression went down so much in such a short time. Remembering back I performed the first compression test (154,154,152,154) before I changed the oil for the first time. A couple posts back are the newest results, depressing huh?

Anyways, is there any merit to what he said at all? Could I actually havent hurt the engine by putting synthetic in?

 

[I_eat_DSM's]

It's possible. My friend put some synthetic in his 225k mile 5.0 after it had 225k miles of great service on dino oil, and about 1500 miles into the synthetic all the deposits and gunk that the dino oil left came apart and the old 302 ATE IT.

I would look at the mechanic's words as nothing more than a theory as to why you lost that compression.

 

[Ski Bum]

It's possible. My friend put some synthetic in his 225k mile 5.0 after it had 225k miles of great service on dino oil, and about 1500 miles into the synthetic all the deposits and gunk that the dino oil left came apart and the old 302 ATE IT.

I would look at the mechanic's words as nothing more than a theory as to why you lost that compression.

Do you remember a few posts back where I said that a black carbon substance was spitting out of the exhaust? Well its doesnt do that any more. Not sure if thats a coincidence or not but it sure seems as if that may have been the gunk that was holding everything together that was slowly expelled through running the synthetic. makes you wonder.

 

[I_eat_DSM's]

It's possible but I doubt that it caused the exhaust thing.

How many miles are on the odometer?

 

[Ski Bum]

It's possible but I doubt that it caused the exhaust thing.

How many miles are on the odometer?

114k.

 

[I_eat_DSM's]

That's a pretty good case for the compression.

 

[Ski Bum]

That's a pretty good case for the compression.

Agreed but why would it have dropped 30+ psi in less than 2 months?

Maybe theres no real explanaition, I'll now just have to deal with it. What do you know about rebuilding engines? I'd like to look into pulling things apart and replacing worn rings, bore/hone cylinders inspect valves, head gasket, studs, etc etc. Obviously this motor is not going to support the 300whp I'm aiming for unless I want it for only one day

BTW I've been trying to give you more rep points for all of your help but it keeps telling me I have spread more around before I can give more to you.

 

[I_eat_DSM's]

Ah it's cool man I don't mind. I'm not here for the little bar I'm really just here to help out other DSM'ers, but especially newer ones who show the potential to learn and fix their own car. You've done a good job with it man!


Taking apart a bottom end gets tricky if you've never done it before. Since 6 bolt blocks are so cheap I'd recommend getting a six bolt block and an engine stand, and piecing together a motor. I'm sure there are a few decent guides on the net, and I believe that the Chilton's manual actually has pretty good instructions on assembling a motor. Personally I'd get all of the parts together and take it to a machine shop and have them assemble the bottom end, and then you can put on the oil pan etc and install the front case/oil/water pumps.

It's not terribly difficult, and you could build the entire top and bottom end by yourself if you'd like, but I would recommend having someone who has some 4G63 experience there to help.

 

[AWDPetmitsu]

While the car was at the dealership the other day, I had an interesting talk with the service writer about the car and what I had done to it. I expalined that the engine lost about 20-25 psi of compression per cylinder. The first thing he asked me was, "Is there oil in it?", duh! but a good question nonetheless. I told him I had just changed the oil and filter with Mobil One synthetic. He then asked me if the previous oil was synthetic. I didnt know as the previous owner didnt know either He told me that if it was regular oil before then I could have actually hurt the engine by putting in synthetic at this point. I havent read anything to back this up but he said that all of the synthetic conditioners in mobil one (and other synthetics apparently) could have dissolved the "gunk" and "stuff" helping the rings seal the cylinders. He said that might explain why the compression went down so much in such a short time. Remembering back I performed the first compression test (154,154,152,154) before I changed the oil for the first time. A couple posts back are the newest results, depressing huh?

Anyways, is there any merit to what he said at all? Could I actually havent hurt the engine by putting synthetic in?

This is the exact reason I don't run synthetic oil in my cars. A lot of people will argue that it used to be an issue before and not now, but I disagree. I'd rather do more frequent oil changes than open a can of worms.

 

[Ski Bum]

Ah it's cool man I don't mind. I'm not here for the little bar I'm really just here to help out other DSM'ers, but especially newer ones who show the potential to learn and fix their own car. You've done a good job with it man!


Taking apart a bottom end gets tricky if you've never done it before. Since 6 bolt blocks are so cheap I'd recommend getting a six bolt block and an engine stand, and piecing together a motor. I'm sure there are a few decent guides on the net, and I believe that the Chilton's manual actually has pretty good instructions on assembling a motor. Personally I'd get all of the parts together and take it to a machine shop and have them assemble the bottom end, and then you can put on the oil pan etc and install the front case/oil/water pumps.

It's not terribly difficult, and you could build the entire top and bottom end by yourself if you'd like, but I would recommend having someone who has some 4G63 experience there to help.

I do actually have an extra 4G63T block sitting in the back of my 1957 Chevy pickup. I'm not sure of the condition as the owner wasnt sure what was wrong with it. Maybe I'll get an engine stand for it and start tinkering and like you said build up the motor then swap it with the one I'm running.

I do however still have an idle surge problem that I would like to fix. I just ordered a pocket logger so that should help me with some general engine information. Also I'm going to replace the ECU coolant sensor with a new one and the fan switch possibly. Only the radiator fan on the left turns on. The smaller one on the right never seems to turn on. I have removed the A/C compressor belt, shoudlnt it still turn on? I am not having any overheating problems, the water temp gauge never goes past 12 o'clock. Oh, and when I replaced the thermostat I used a 160* unit should I have gone with a higher temp?

This is the exact reason I don't run synthetic oil in my cars. A lot of people will argue that it used to be an issue before and not now, but I disagree. I'd rather do more frequent oil changes than open a can of worms.

For me it wasnt to last longer between oil changes. With whatever oil I run it will be changed every 3k miles. I went with the synthetic because I have had very good results with in the past with my WRX's and because it was reccomended here. Hopefully the synthectic oil wasnt the culprit in my recent problems.

I'm curious if now that I have run synthetic I can switch back to dino? I have maybe put 500 miles on the car with synthetic. Also would moving to a heavier grade oil help the engine seal any better?

 

[I_eat_DSM's]

Moving back to dino won't help your compression but it will make you less prone to have leaks.


You could try blocking your FIAV and removing the hoses and see if that helps with your surge problem. I would check your ISC and make sure it's good, and as long as you do not have any boost leaks and your timing is good then I'd give the ISC a try.

 

[Ski Bum]

Moving back to dino won't help your compression but it will make you less prone to have leaks.


You could try blocking your FIAV and removing the hoses and see if that helps with your surge problem. I would check your ISC and make sure it's good, and as long as you do not have any boost leaks and your timing is good then I'd give the ISC a try.

Correct me if I'm wrong but wouldnt blocking the FIAV only affect cold starts? That is the one instance that the engien does what it should. When cold starting it fires right up and rises to 1800+- rpms and then gradually drops to 900+-rpms.

Its when the car is warm when the idle problems occur. Now whats happening is that the idle will drop really low, about 5-600 rpms which makes the car vibrate like no other. Other than that it hasnt surged above 1k rpms in a couple days now.

I'll check the ISC next and try to eliminate that or identify it as the culprit.

 

[I_eat_DSM's]

Proper startup is around 1200rpms cold to about 800rpms warm. May wanna try turning the BISS screw in a little farther to see if you can get it closer to that range.

 

[Alexvw]

Did you ever fix this? Yes that is a 4g63 in a vw beetle

You can hear my idle "hiccup" and "stumble" intermittently near the end of the video, just like you have described to be your original problem. I need to check vacuum and boost leaks because I think that is the issue here but I need to buy or make a tester.

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