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Old 10-13-2005, 12:13 PM   #1 (permalink)
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Default Stuttering, rough idle, low power, bad gas mileage

I have a 93 VR4 that's fairly stock. I bought an HKS intake from Brian locally back in June. I had my tranny rebuilt over the summer. My car has 125K on it now. I did the full service at 119K.

During the tranny rebuild, I gutted my rear precat and added a downpipe.

Since then, I get rough idle after the car is warmed up, some intermittent stuttering, like the car is missing or something, and occassional backfires too. I know I don't have an ounce more power than before I did the DP and got rid of the cats. The thing that bothers me the most is the terrible gas mileage. I used to average 20-22mpg, now it's 16-18mpg max. Any suggestions on what's going on?

I did go ahead and add an HKS EVC EZ, and a boost gauge. I replaced my PCV valve which helped a little. I did a pressure test several times, and the only leak was from the bad PCV valve, which is now fixed. Even when I boost up to 15psi on the aftermarket gauge, the car barely feels more than it did when I just did the free boost mod. I thought I'd feel some major punch after adding the EVC, but I haven't. any chance it's the EGR valve?



Thanks,

Carlos
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Old 10-13-2005, 05:08 PM   #2 (permalink)
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Default Re: Stuttering, rough idle, low power, bad gas mileage

I doubt it's the EGR valve...or else people like me wouldn't use block off's. Being as you have a 93, you could run with the EGR removed and blocked off, without getting a CEL. Your problem could be one of many. You need to be more specific about what services you have recently done to the car. If it were my car, the first things I would check would be the ignition and fuel systems. ie- Make sure you have good wires and good plugs that are properly gapped. Running at 15 psi, you would probably want to at least hotwire the stock fuel pump too. Since you were not specific as to WHEN you have these issues, it's hard to help. For instance, if it was stuttering bad and jerking at WOT around 5000-5500 Rpm's, you may be experiencing spark blow out due to the 15 psi of boost, and you Might have to gap the plugs down and or hotwire the pump. It really depends on the individual car, but generally, after 14 psi on a stock fuel system, enough people have problems with spark blow out, that it should be a concern.

Of course, there are many other things to check , but again...we need more specific information to better assist you. It could be bad coils, a bad PTU, the CAS might be on the fringe of going bad, maybe the injectors are not flowing right, etc etc. After checking plugs and wires, I'd then, hotwire the stock fuel pump or buy a Walbro or something. Hopefully you have a decent boost gauge, and it's not off by much. Some are bad enough to be a few psi off. If that's the case, you may be running upward of 16 or 17 psi on a stock fuel system...not good! Get back, and let us know when the problems occur, and what EXACTLY you have replaced recently, etc.
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Old 10-13-2005, 05:13 PM   #3 (permalink)
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Default Re: Stuttering, rough idle, low power, bad gas mileage

do you have a logger? your 02 may be bad or could have been damaged during your precat removal.
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Old 10-13-2005, 06:25 PM   #4 (permalink)
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Default Re: Stuttering, rough idle, low power, bad gas mileage

I have KINDA this problem. I have *decent* power (wastegate pressure but my gas mileage is HORRIBLE. I get 120 miles/tank. And thats driving *slow* If I drive fast, it gets even worse ! (I'm talkin 3 notches on the gas-o-meter in 10 miles)

Reason? My IDC's are 300%. My rear 02 sensor is reading 4.97V cruising. When you let it idle, it idles @ 1000'ish rpm, and then it drops down to like 700 sometimes. Then it kinda misses and starts to sound like a harley. You rev it when it's in that state, and it misses a little bit, and then the rpm is normal again.

We just logged yesterday, and I'm probably going to wind up fixing this thing in 3 or 4 weeks...(Not my DD, and i'm saving $$ for school + books)
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Old 10-13-2005, 06:31 PM   #5 (permalink)
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Default Re: Stuttering, rough idle, low power, bad gas mileage

Quote:
Originally Posted by 2Slow2Tedius
I have KINDA this problem. I have *decent* power (wastegate pressure but my gas mileage is HORRIBLE. I get 120 miles/tank. And thats driving *slow* If I drive fast, it gets even worse ! (I'm talkin 3 notches on the gas-o-meter in 10 miles)

Reason? My IDC's are 300%. My rear 02 sensor is reading 4.97V cruising. When you let it idle, it idles @ 1000'ish rpm, and then it drops down to like 700 sometimes. Then it kinda misses and starts to sound like a harley. You rev it when it's in that state, and it misses a little bit, and then the rpm is normal again.

We just logged yesterday, and I'm probably going to wind up fixing this thing in 3 or 4 weeks...(Not my DD, and i'm saving $$ for school + books)

lol are you sure you arent leaking gas somewhere, 6mpg when your easy on it is ludicrus, ecu toast maybe?
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Old 10-13-2005, 06:44 PM   #6 (permalink)
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Default Re: Stuttering, rough idle, low power, bad gas mileage

I WAS leaking gas out of the exhaust. That's how rich I was running. There was black smoke coming from teh car @ idle. Then I changed the 02 sensors (bosch universals) and spark plugs and it went away...I thought. The gas mileage isnt was bad as it WAS (one time, i spent $181 in 3 days !) but it bugs me that I cant drive to the beach without using a 1/4 tank....a 20 gallon tank @ that.

I think its because when I installed the new 02 sensor in the back, I plugged it in, and then screwed it in...resulting in the wire/cord getting twisted like 300 times.

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Old 10-17-2005, 12:25 PM   #7 (permalink)
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Default Re: Stuttering, rough idle, low power, bad gas mileage

Quote:
Originally Posted by 93VR4nPhilly
I doubt it's the EGR valve...or else people like me wouldn't use block off's. Being as you have a 93, you could run with the EGR removed and blocked off, without getting a CEL. Your problem could be one of many. You need to be more specific about what services you have recently done to the car. If it were my car, the first things I would check would be the ignition and fuel systems. ie- Make sure you have good wires and good plugs that are properly gapped. Running at 15 psi, you would probably want to at least hotwire the stock fuel pump too. Since you were not specific as to WHEN you have these issues, it's hard to help. For instance, if it was stuttering bad and jerking at WOT around 5000-5500 Rpm's, you may be experiencing spark blow out due to the 15 psi of boost, and you Might have to gap the plugs down and or hotwire the pump. It really depends on the individual car, but generally, after 14 psi on a stock fuel system, enough people have problems with spark blow out, that it should be a concern.

Of course, there are many other things to check , but again...we need more specific information to better assist you. It could be bad coils, a bad PTU, the CAS might be on the fringe of going bad, maybe the injectors are not flowing right, etc etc. After checking plugs and wires, I'd then, hotwire the stock fuel pump or buy a Walbro or something. Hopefully you have a decent boost gauge, and it's not off by much. Some are bad enough to be a few psi off. If that's the case, you may be running upward of 16 or 17 psi on a stock fuel system...not good! Get back, and let us know when the problems occur, and what EXACTLY you have replaced recently, etc.
Here's what's been done:

The car ran fantastically at 119K. I decided to go ahead and get the 120K done. I went to a local mechanic that I trust. He did the service by the book, according to him. I saw all the parts, but can't remember it all. It was done in February.
After I got the car back, it didn't pull as hard as it did before, and my gas mileage decreased a little. I thought it would just take a little time for it to get back up to speed. I remembered that when I took my Maxima in for service, this was at the dealer, it had a similar effect, but after a while things got back to normal. It never got any better with my VR4. I did discover a couple of boost leaks then got them taken care of.
Next, I bought an HKS intake from a local member. It didn't help my performance at all! I kept it because I thought it would be good for down the road, which is now.
I drove the car like that for a few months, until late April. Then my 3rd gear synchro went bad.
I had the tranny rebuilt locally. While it was out, I decided to go ahead and do some basic mods.
I gutted the rear precat while it was still on the car, and added a downpipe, which eliminated the front precat and the main cat as well..
After installing the tranny, the car drove well. This is when I first noticed the hesitation. It happens while accelerating anywhere from 30% throttle to WOT. It especially stutteres when the car is cold. It didn't stutter before the tranny, dp install. It also backfires in the tailpipe randomly, but not often. It also idles rough after it's warmed up. The tach is steady, so my rpm's aren't going up or down. It feels almost like when a spark plug wire isn't on tight and one cylinder isn't firing. Also, I know the clutch isn't slipping at all. I can look at the tach and see that. I've tested the clutch in every possible way.
When I accelerate the car sputters, but not hard; not like fuel cut. I had a BPU Supra, so I know what fuel cut feels like.
I thought it was the boost solenoid, so I borrowed one from a friend. The car ran exactly the same. I also added a boost gauge, so I could monitor boost. I've pressure tested the car up to 20 psi. It holds just fine.
I next added an HKS EVC. I can turn the boost all the way up to 15. It pulls pretty hard, but not much harder than before I did the tune-up a few months ago. It seems like after all this I should have at least 30 more horsepower. But I feel less of a difference now than when I did the free boost mod. I really felt a difference when I did the free boost mod. But after an intake, all cats removed, downpipe, intake, and a EBC, I should feel some real power, but I dont feel much.
The things that concern me are:
1. lower gas mileage. Formerly 20-22, now 16-18.
2. Stuttering upon acceleration, especially when cold.
3. Rough idle, but only when car is warmed up. Not when car is first started.
4. Less power than what should be there.

Thanks
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Old 10-17-2005, 02:36 PM   #8 (permalink)
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Default Re: Stuttering, rough idle, low power, bad gas mileage

Quote:
Originally Posted by carlosinseattle
1. lower gas mileage. Formerly 20-22, now 16-18.
2. Stuttering upon acceleration, especially when cold.
3. Rough idle, but only when car is warmed up. Not when car is first started.
4. Less power than what should be there.
ALL those signs point to rich. Since the only thing you did was downpipe/precat, I'll bet you anything that one or both of the O2 sensors were either damaged or not reinstalled correctly. Or, the dp wasnt installed securely enough and there is a massive leak somewhere near an O2 sensor. If you can, try and log it, if not, get back down there and double check. Since this all happened right after the rebuild/downpipe, you should assume something either of you did caused it. The guy who rebuilt your tranny could have accidentally broken/moved/forgot something when putting everything back together, but your symptoms definitely show rich.
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Old 10-17-2005, 04:49 PM   #9 (permalink)
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Default Re: Stuttering, rough idle, low power, bad gas mileage

OOOHHH SHIT ! Jen, i forgot completely an exhaust leak'll fux with an 02 sensor !!!! Man, I just replaced my rear one and its STILL actin shitty! OMGOMGOMG you da (wo)man!

Man, I got a HELLA exhaust leak on my rear precat! (And thats the 02 sensors thats fuxxed)
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Old 10-18-2005, 02:08 AM   #10 (permalink)
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Default Re: Stuttering, rough idle, low power, bad gas mileage

Quote:
Originally Posted by 2Slow2Tedius
OOOHHH SHIT ! Jen, i forgot completely an exhaust leak'll fux with an 02 sensor !!!! Man, I just replaced my rear one and its STILL actin shitty! OMGOMGOMG you da (wo)man!

Man, I got a HELLA exhaust leak on my rear precat! (And thats the 02 sensors thats fuxxed)
ron probably crushed your stock gaskets on the precats when he did the crappy rebuild on your engine. get some new ones from mits. those things are a bitch to do tho...that rear precat is torture to get back in . and my car has half the brackets, egr ect. removed already
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