'98 GSR with:
SC34(57trim)
ramhorn
3 inch exhaust
3 inch cat
closed loop dump
750cc injectors
255lph hp Walbro
PowerFC EMS
stock ignition

Driving to work last night the car started acting funny. When I get on it, it will start to accelerate as usual, but then it's like it hits a wall. The car starts stumbling and bucking. Car is NOT smoking or blowing coolant, oil and water temps are fine, oil pressure is fine and fuel pressure is normal. I checked and do not see any fuel leaks. Cold idle is normal but warm idle seems to be a bit jumpy. Car doesn't shut off, but sometimes it seems like it's about to. When it's doing this, the wideband is reading between low 12s and high 10s, and jumping around a lot. One time I think the readout just said rich, but I cannot be sure. Usually I'm seeing high 11s to low 12s.

The problem seems to be worse in higher gears. In first I can usually get near 4k rpms before it starts but in 3rd and up it usually, but not always, starts between 2k and 3k. It doesn't feel like there is a blockage anywhere (had a car with a cat that went bad and was choking the engine) because it surges and is not down on power until it gets to about 3 psi. I haven't really started working on the car yet to figure out what is wrong...but I get the feeling it is electrical.

Last week I noticed the car would occassionally break up at the top of second gear and then the other day it started stumbling in second gear. I thought maybe it was the plugs, so I changed them last night. The cap, rotor, and wires have less than 7k miles on them. Car was tuned last Jan and has been running flawless up until this point, so I don't think the tune is the problem.

Anyone have any ideas? I plan to do a compression test later today...but I don't think it's something physical in the engine because it still pulls strong in first before it starts running like ****.

Thanks in advance.

 

Just pulled the plugs. Granted, I didn't do a shut off after a full throttle pull and had it idling in the garage, but the plugs are jet black. They aren't wet, but the insulator is solid black. The plugs look like they have been in there for a long time even though I put them in last night and drove @ 30 miles on them. Gap is set at 28 and fuel filter has less than 7k miles on it.

Looked at the voltage display for tps, it's 4.77 at full throttle and 0.54 with throttle closed

Map sensor is showing 2.67 with key on but engine not running.

Air/water temp sensors appear to be working.

Car smells like it is running very rich, but wideband is reading normal.

 

Do you have a wideband on the car? Sounds liek your temp corrections are way off and causing yoru issue. Did dyou have a recent temp change and then the car started to run like crap? also do a leakdown and compression test. Would could have also foul a few plugs try changing them out.

 

Wideband is in the car. I'm going to do a compression test later today. The temp has changed recently, but a few weeks ago we had a similar temps and I had no problems. Car also ran fine last winter during cold spells.

 

well if you have a wideband in the car what are your a/f under boost vs the other day when it was warmer out so to speak. I know my temp corrections are all mnessed up because i ahvent had time to retune my setup when switching from gsr cams to ctr cams. there is a certain ambient temp that it runs fine and once temp drops i got lean in boost and rich part throttle so id have to say tahts more then likely your issue

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Turbo-LS &raquo;</TD></TR><TR><TD CLASS="quote">well if you have a wideband in the car what are your a/f under boost vs the other day when it was warmer out so to speak. I know my temp corrections are all mnessed up because i ahvent had time to retune my setup when switching from gsr cams to ctr cams. there is a certain ambient temp that it runs fine and once temp drops i got lean in boost and rich part throttle so id have to say tahts more then likely your issue</TD></TR></TABLE>

Mentioned this is my first post.

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by 1158 &raquo;</TD></TR><TR><TD CLASS="quote">When it's doing this, the wideband is reading between low 12s and high 10s, and jumping around a lot. One time I think the readout just said rich, but I cannot be sure. Usually I'm seeing high 11s to low 12s.</TD></TR></TABLE>

That's when I'm full throttle. At part throttle the car runs pretty much like it always has. I get a few hesitations, which didn't happen before, but it is driveable. Wideband reads low/mid 14 in part throttle...which is normal.

As for a retune...there have been no changes to the setup since the last tune.

 

Just had the car idling, pulled the map plug and the idle gets very erratic and then the engine shuts off.

 

hmm how many miles on the setup? possibly an injector clogging up? how old is the fuel filter? are you logging fuel pressure that you know for its its not loosing any?

 

Boosted for about 7000 miles. I replaced the fuel filter, cap, rotor, plug wires, O2 sensors when I did the turbo install.

I don't have a fuel pressure log, but my gauge on the fuel rail is where it usually is at idle...around 40 psi. Using stock fpr. Wonder if the fpr could be bad. I did not change it when I did the install.

 

Turbo install?

Did you put a new one on, whats the story on that. And did the problems come up after this was done?

Do you have any vacuum lines that may have came loose anywhere?

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by JDMs1eeper &raquo;</TD></TR><TR><TD CLASS="quote">Turbo install?

Did you put a new one on, whats the story on that. And did the problems come up after this was done?

Do you have any vacuum lines that may have came loose anywhere?</TD></TR></TABLE>

No, I mean when I did the install 18-20 months ago...since then I have put about 7k miles on the car. The last time I made any changes was swapping GSR cams for CTR cams last Jan. I had the car retuned after that and have not had any problems until just recently. I checked all the vac lines I could find and don't see any loose/cut/ripped. I also don't think it is vac...I had a line come loose about 2 months ago and that was completely different.

I do want to say thanks for the help so far. This is pissing me off. It'll probably end up being something stupid/simple...but I'm at a loss as to how to figure it out.

 

Just tested the fpr per Helms...looks like it works.

With vac line off and plugged fuel pressure was 55-60 with line on it was 45-50.

 

Ok, I put the old plugs back in but still having the problem. I noticed my injector duty cycle is near 60% yet I'm only hitting about 7psi. I usually don't see 60% until I get near 9-10 psi.

Anyone think it could be tha MAP sensor?

Oh yeah, did compression test...all cyclinders were good.