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Old 05-25-2002, 11:57 PM   #1
dyswtric27
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Question Studdering on boost?

As you guys know i had a lot of trouble with my turbo after TRI installed it. Anyways ive started to have another problem creep up here.

About 2 weeks ago i would get some hesitation and stutter at around 4000 rpm when on boost. This gradually got worse and worse, and this past weekend i put in the svx fpr and did the parallel fuel mod, and now its horrible. Once i reach boost past about 3 or 4 psi the whole car just stutters and it doesn't really pull. The boost will climb to 6 psi like it should but the EGTs drop way down to like 1200 and it just doesn't pull. The thing thats weird is that at about 1/2 throttle i can keep it at 3 psi and pull nicely. Its just once i go WOT the car stutters.

I am possibly thinking its my plugs, and one or more aren't firing under boost. They are still the stock champions (i know, i know, im replacing them this week ). I have tried adjusting my rrfpr every way i can and it doesn't really seem to make that much of a difference.

I talked to Tom over at ludespeed and he said check that, and then if worse comes to worse get a compression check (which im really scared to do).

You guys (and gals) have any other possibilities to check?

Jason
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Old 05-26-2002, 12:01 AM   #2
HndaTch627
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sounds like whatever you are using to clamp the Map sensor is failing.

jeremy
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Old 05-26-2002, 12:11 AM   #3
dyswtric27
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Yeah, thats also what i thought. So i hooked up a voltmeter to the actual map wire running into the ECU and it never breaks 4.7v. I set the SS voltage clamp intentionally a little low to try and make sure that wasn't the problem. I have even tried lowering it to around 3.9 and still have the problem.

Jason
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Old 05-26-2002, 03:35 AM   #4
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hmmm...odd, it's acting like fuel cut, have you tried to watch the knock sensor during all of this, that's right about the time the ECU goes to open loop.

jeremy
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Old 05-26-2002, 06:55 AM   #5
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I'm thinking O2 sensor.
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Old 05-26-2002, 03:36 PM   #6
dyswtric27
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How can i check to see if its the knock sensor? And when does the ecu go into open loop, like 50% throttle?

Also which 02 sensor do you think it is, front or back and how can i check if its dead or not. Its probably the front since i was running extremely rich for a while.

Jason
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Old 05-26-2002, 04:44 PM   #7
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Probably front.

You could always unplug it, drive it, and see if it makes any difference.
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Old 05-26-2002, 05:09 PM   #8
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It can't be the O2 sensor if it only happens in open loop. It's not reading off it at all then... if it only happened in closed loop, then it'd be a very good possibility, though.

What does the studder feel like? Does it feel like a lack of boost, a lack of fuel, a small ignition cut, some unidentifiable hiccup? Do you notice anything going on with your EGT's, A/F's, or boost when it occours?

I would doubt it being a compression problem if the car runs just fine at idle, where you'd notice it the most. At WOT, the car has very little chance to lose boost out the rings (due to, say, a common crown breaking off), and at idle the vacuum and rotation of the motor is so low that it'd be much more likely to run roughly (BTDT).

How are you controlling timing? It's possible that it's at the threshhold where the ECU may hear detonation and pull timing, causing a dip there. Wish there was a simple knock-link circut that could be made to test this...

I'm going to guess that it's detonation due to low/lack of fueling and advanced timing.
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Old 05-26-2002, 09:17 PM   #9
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Hey 8,

The studder feels like a lack of ignition or a lack of fuel. The boost stays solid at 6 psi and really doesn't move. When i get on the throttle the EGTs drop real quick, to around 1200 where they are usually around 1400-1500.

As for timing i am using the J&S ultra safeguard. I have it retarding 1/2 degree per boost starting at i guess 3 psi or 5 psi (whatever the start knob all the way clockwise is). I will try disconnecting the J&S this week and see if that changes anything.

I do think that the ecu is either pulling fuel or retarding the timing. I am definitely going to invest in a fuel pressure gauge to make sure im fine, but im pretty sure im getting plenty of fuel.

So what should i do or test??
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Old 05-26-2002, 09:22 PM   #10
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Quote:
Originally posted by dyswtric27
As for timing i am using the J&S ultra safeguard. I have it retarding 1/2 degree per boost starting at i guess 3 psi or 5 psi (whatever the start knob all the way clockwise is). I will try disconnecting the J&S this week and see if that changes anything.
Don't mean to scare ya, but I wouldn't disconnect that J&S and run under boost unless you had a second motor laying around.

Are you throwing a CE light? If so, what is it? This would be a very important piece of the puzzle. Could be fuel, could be detonation, could be MAP voltage.
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Old 05-26-2002, 09:30 PM   #11
dyswtric27
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Ha, yeah good idea about the J&S. I have had a CEL for like 2 years now. Can't get rid of it. This was even before the turbo, it was 02 sensor, i replaced it and subaru could't even figure it out. So i basically just ignore it. I can run up to subaru sometime and check the code or is there an easier way?

Also i was looking at getting the Nordskog digital fuel pressure gauge, just something cheap to check my fuel while i tune and then hide in the glovebox or something. Is this an decent gauge, my friend uses one in his conquest tsi.

Anyways, what are the possible things that would throw a fuel cut or retard the timing?
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Old 05-26-2002, 10:47 PM   #12
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i know that a friends wrx had a problem with maxing the injectors out, that resulted in a similar studder feeling when on boost. or is it possible with the low egt's that youare running very rich bogging a bit due to all the fuel. i know my friend but a set of sti injectors in and no longer has the problem, not it just runs rich as all hell.

kevin
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Old 05-28-2002, 01:07 AM   #13
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When I had that problom, I had a bad #3 plug wire and was dumping unburned fuel out of #3 cylinder, EGT's dropped to 1200, and I fouled the plugs and O2 sensor.
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Old 05-28-2002, 01:14 AM   #14
dyswtric27
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Thanks for your help, i haven't gotten a chance to really take a look at anything yet as i was at my girlfriends graduation. On the way home i basically discovered this, as soon as the boost hits like 2 or 3 psi, or the MAP voltage coming in reaches 4.85 or so the studdering happens. I have the SS voltage clamp in there and i can read the voltage going to the ecu and it is below 4.85 so im not really sure.

It really feels like a fuel cut, the motor just doesn't pick up eventhough there is plenty of boost. The EGTs drop which makes me think its pulling fuel and the timing. I will take a look at all of my wiring tomorrow, maybe something came loose. I'll let you know.

Jason
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Old 05-28-2002, 09:00 PM   #15
dyswtric27
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Well i went out today and replaced the plugs with bosch crap, just the stock heat range since i couldn't find the NGK BR8ES's i wanted anywhere around.

Cleared up the problem completely. Thanks for your help, i love you.

Jason
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Old 05-29-2002, 12:08 AM   #16
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Doh!

I knew it was a spark problem, just not in all 4 cylinders...
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Old 05-29-2002, 05:39 PM   #17
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I've had and still do have a similar problem.

Keep and eye and an ear on it dyswtric27, I bet it comes back.

When I bought my car (already turboed and tec'd) he was still running the Champions (W.T.F?) I changed out the plugs and it ran great!
Now it is doing it again. I know that I am running rich, but I am still too timid to pull back some fuel. I guess I'll have to take the risk!

-Nathan
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