It is time for a tune-up on my VR-4. About 16k miles have past since my last tune-up.

The car only does this at startup, once it is warm you can only notice slight hesitation.

So I'm going to do the plugs and wires soon.

Does anyone else have this issue where they just don't get enough miles between tune-ups? I have NGK platnium plugs at the stock heat range.

Could it be my injectors? My low fuel trims is 80% which is as low as the ECU can go. At +120k miles could the injectors be leaking. I get no codes from the ECU using TMO. My exhaust tips are always black with carbon.

Could the bad flex section in my downpipe cause bad O2 readings? I have carbon on the under side of the hood from this hole.

Anyone think I need new O2 sensors? I've heard that OBD-I O2's need to be replaced every 60k miles. They cycle in closed loop mode.

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1992 3000GT VR-4
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3SI Member 0660, 1753, 2038
W3SI Member 15

Any leaks in the exhaust before the catback will cause the motor to run real ruff. Do you hear a "tapping" sound under the car while the motor is running.

Any mods done to your car?

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06 Blue EVO 9

I just went through soemthing very similar with a crack just after the two downward sections of the frontpipe came together.
What it does is suck clean ait in before the O2 sensor. Causing it to read lean. The ECU then over compensates for the lean reading and dump extra fuel into the motor. which is why your trims read so rich in the low RPMs. In the higher RPMs you are pushing much more air and the crack(leak) has air being forced out more than clean air being sucked in.
I would get it fixed soon, because my leak caused my O2 sensor to get extremely carboned up from running so rich. My IAC motor also burned out about the same time. which could have been caused by it getting carboned up and having to work overtime to keep a steady idle.

When you get plugs, don't go back to platinums. They dont conduct too well in boosted aplications. I'd just run a simple copper plug at a slightly lower gap if you if you run increased boost.

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~Joe - aka spider gear destroyer
'94 Stealth R/T
-Lightly Modded ;)

My exhaust has had a bad flex section for about 4 years. It runs fine most of the time. The car backfired and blew out the flex because two plugs and wires were bad.

It only studders when the car is cold and at part throttle. When I am at full throttle or the car is warm I don't have a problem.

I don't think I have rod knock or bearing failure. I don't really have any lifter tick that I can hear either. I just changed my oil in April and it still looks good.

The last 3 tune-ups have lasted less than 14k miles a piece.

I have a K&N FIPK and the free boost mod.

The car used to get good gas mileage (28-30+ mpg) now I feel lucky if I get 16 mpg. I used to drive expressway everywhere and now I use city streets more which could be part of the mileage problem.

Maybe I have an intake track leak. I was always going to check that but never got a chance.

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1992 3000GT VR-4
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3SI Member 0660, 1753, 2038
W3SI Member 15

My O2 sensors are before the crack. Unless I have a manifold crack

I got a new IAC January 2003. They do fail with time.

I guess I'll bite the bullet and buy an ATR DP. It seems to be the cheapest and best.

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1992 3000GT VR-4
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3SI Member 0660, 1753, 2038
W3SI Member 15

I wasn't getting at that. The tapping sound would be the sound of exhaust escaping.

The reason it probably never gave you problems in the past is because the hole wasn't large enough. While it's cold the metal expands and contracts as it heats up just enough to shrink the hole. At WOT the exhaust is moving at such a great velocity it passes right by the hole.

The thing is, a hole in the flex pipe won't turn your under hood insulation black. You might have another one closer to the head. Where exactly under the hood is the soot?

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06 Blue EVO 9

Actually, for the purpose of testing, places like checker sell fiberglass exhaust patch kits for ~$12. It's a temp fix (overtime it will blow out again), but it will definately eliminate this variable.

Soot is on the firewall, back of the intake, and a big spot on the metal plate on the under hood by the EGR. The soot isn't black, more of a light brown coating after 4 years of accumulation.

In Feb 2001 I put a wide stainless exhaust clamp from NAPA over the flex section to kind of patch it. It leaks past it for sure because the area is black and smoke comes out there. My car is way too loud, hmm maybe I have a blown exhaust gasket.

I've seen smoke rise off the downpipe and up the back side of the motor before I put on the clamp. I never thought about a second leak.

I guess I have to pull my heat shields then suck some Seafoam into the brake booster line. The smoke should show all the leaks if I can see through all the smoke.

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1992 3000GT VR-4
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3SI Member 0660, 1753, 2038
W3SI Member 15

Damn I want to go home and start wrenching.

I have to keep the car driving for the next two days though. The car is going to a 4 hour detail job tomorrow morning and Saturday is the Brewer game.

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1992 3000GT VR-4
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3SI Member 0660, 1753, 2038
W3SI Member 15

The car is up on jackstands.

The oxygen sensor goes to 0 volts for a second or two every time I step on the gas and release it. Smoke comes out all over the place.

It seems like the rear manifold is the leaky spot. Since the rear is cast I don't think it cracked.

I'm guessing a stud or two broke and/or the gasket failed.

I'm going to order;

(2) 12010 MD168115 GASKET,EXHAUST MANIFOLD
(1) 12298L MR188537 GASKET,CATALYTIC CONVERTER,LH
(1) 12298R MB687002 GASKET,CATALYTIC CONVERTER,RH
(1) 13010B MB687002 GASKET,EXHAUST PIPE
(1) 13010BB MB687002 GASKET,EXHAUST PIPE
(1) 13010C MB687004 GASKET,EXHAUST PIPE
(1) 13010D MB687004 GASKET,EXHAUST PIPE
(1) 12024 MD149764 GASKET,EXHAUST MANIFOLD EGR

(2) MD168115 $25.97 = $51.94
(1) MR188537 $3.54 = $3.54
(3) MB687002 $5.74 = $17.22
(2) MB687004 $4.65 = $9.30
(1) MD149764 $4.31 = $4.31

Total $86.31 + S/H

Should I order Mitsubishi hardware or replace things with hardware store stuff?

Do two gaskets come in MD149764 GASKET,EXHAUST MANIFOLD EGR?

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1992 3000GT VR-4
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3SI Member 0660, 1753, 2038
W3SI Member 15

I'd personally get the Mitsu stuff. It'd be no fun having to do that stuff 2x.

Yeah, getting the mitsu stuff, especially with the discounts we get from kuetner and renner, its def worth it.

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~Joe - aka spider gear destroyer
'94 Stealth R/T
-Lightly Modded ;)

To bring a dead thread back from the grave.

I did the plugs and wires in October.

The things that I found that could cause stumbling were the vacuum hose to the FPR was ripped in two (the hose was not the same type or quality as the rest), the EGR pipe is broken at the flex section, the EGR valve was stuck open, and the brake booster vacuum line leaks.

I cleaned the EGR valve, replaced the vacuum hose, and bought a EGR pipe that is still sitting in the box. The studdering is infrequent now but truly cold weather is still coming.

I'm thinking the fuel pump needs replacement.

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1992 3000GT VR-4
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3SI Member 0660, 1753, 2038
W3SI Member 15