Low Boost, Feels Underpowered, etc..????

Dustin Yenny

Registered User
I'm looking for some ideas on a problem with the '93 SC I am buying. Tad removed the chip and the car seems to run good now. The problem I noticed is the car just does not seem to feel fast. I mean the stock '91 5spd that I sold Dave Dalke would stomp all over this '93....regardless that its automatic....it just doesn't seem to have any get up and go. My SVX would probably stomp it.

My thinking is the fact the exhaust he has is a true dual from the motor back. No cats, no resonator, and stock mufflers. Ported manifolds too. It appeared to be very large pipes too (possibly 2.5"...maybe a tad bit larger??). The car boosted like 8-9 psi max. It has a 10% OD pulley. I asked he confirmed that he is using the stock S/C belt....so that may be a problem too. Vac at idle is 18-19ish. Vac when you let off the gas going down the road is 21-22ish. That seemed reasonable considering thats where my other SCs always ran....so I don't think there are any Vac leaks.

I just don't know if thats a reasonable amount of boost considering how well this motor can breathe.

Below is a list of some of the mods.

70mm BBk throttle body, 42# injectors, 75mm pro-m mafs, new autolite dp spark plugs with magnecor wires.
10% overdrive pulley for supercharger, underdrive pulleys, K&N cone filter w/cold air dividor, ported heads, exhaust manifolds, and intake plenum, 3" chrome inlet tube, new felpro head gaskets, New IAC, Eibach 1.5" lowering springs, fuel pressure guage, adj feul press. regulator, and dual exhaust.

He also upgraded the fuel pump. Walbro 255 I think. I'm going to ask exactly how everything is set (fuel pressure, etc...) so I know where I'm at with that stuff to get a starting point.

I may have to talk to Phil Kuhn and get his dyno guy to fine tune this. I'm reading that I should not need a chip for this thing to run excellent. I'm thinking the S/C belt might be slipping under heavy throttle and the exhaust system is overkill. I'm going to need to put some cats on this to get it to pass PA state inspection. Can I buy a dual in and dual out resonator or don't they make those???
 
Also sounds like a pretty bad boost leak. You should be getting at least 13-14psi with a 10% pulley.
 
Thats what I thought. I'm just going to have to find someone how knows these cars and pay them to fix it. I know I don't have the patience to tinker with it. I mentioned it might have a boost leak but Tad told me he did some test (pressure test) on the system and he could not get anything to leak. Thats when I started thinking the 10% might need a smaller belt and since he just used the stock belt....it might be slipping under heavy acceleration.
 
I got the car home. I did get it to boost ~11psi when I was really getting on it. It does run really good. The only problem I notice is down low it feels worse than a regular 3.8L bird. I mean the torque I remember from my other 3 is just not there. I can't get it to even chirp the tires. I think this is because of the exhaust.

The exhaust consists of I believe true dual 3" straight pipes from the manifolds back into the stock mufflers. It does not sound very good. The only other thing I think may contribute to this loss of power would be the CEL which I was told was throwing an O2 sensor code.

My thoughts and I don't even know if they are close are: the car should run fine without a chip. I mean the MAF has the right sampling tube for the 42lb injectors. It has the 255lph fuel pump and 70mm TB. Now one or both 02 sensors may be bad and the computer could be going into some preprogramed safety mode...which is designed to run fine on a stock 3.8L S/C motor but not one with the mods I have. This sounds reasonable to me. I mean, the light comes on ~5 miles after you drive it and stays on....if you shut the car off, the light stays off until you drive it that first 5 miles. The light may also have something to do with the exhaust!?!?!

At any rate, I'm going to need to put some cats on this to pass PA state inspection.

So my idea is to put 2 high flow cats from Super Coupe Performance (2.5") along with a dual in and dual out magnaflow resonator also from SC Performance (2.5") and leave the stock mufflers. I honestly don't know for sure what size pipes he used for the exhuast....they seem large....but I'm thinking I'll leave them for now!

So.....comments, suggestions, etc...about my exhaust idea specifically???? I need to order the componets ASAP so I can get them put on and it inspected....

Thanks all!
 
I finally got around to pulling the codes:

Hard Faults:
159-MAF Out of Range

Memory Faults:
172-02 not switching. is or was lean. Right side or rear.
186-Pulse width longer than expected or MAF lower than expected.
189-Lean at part throttle. Left side or front O2 sensor.

Seems like I'm still having problems with the MAF. Can anyone give me an idea of what to check or what they think the problem may be? I remember reading the MAF should have battery voltage and Tad was only getting like 11.8V.....so maybe the MAF isn't getting enough voltage and the output is fubarred up???

Thanks in advance.
 
BTW, those codes were KOEO.

KOER Codes were:
172-O2 not switching. is or was lean. Right side or rear.
225-Knock sensor not tested.
 
maybe the MAF is dead, like so many of us, you should just get a new one, or go to the junk yard and take that lil tool to remove them from the HOUSING and get away with it for free. :D yeah if the MAF is acting up it will cost your horsepower... are u sure there is no turbulence coming in? is it stock INTAKE? or aftermarket?
 
they wont work because the MAFs from a N/A have injectors that push lesh fuel... the SC MAF is calibrated for its injectors and so are the N/A are calibrated for their injectors...
 
Hey dustin this may be a dumb thought but could the problem be within the parts removed for the stereo in the trunk. Is it possible that something that gets hooked up in the trunk could be triggering something in the eec somewhere. I have know idea if this makes any sence but its was just a thought. Its about the only thing I haven tried with the car. I would hook all that back up and see what happens. May change nothing but its worth a shot.
Tad
 
Anyone???

I guess at this point I just need advice. Since I've been driving it, I noticed that it is not as slow as I thought. I mean when I go WOT say from 60mph+ on the highway....I can hit about 12 psi and the car is crazy fast at highway speeds. I mean I can go from 65-110 in a flash. There are times when I can get a good launch and 0-60 seems quick....most times the car is just a dog. I also notice if I go say 1/4-1/2 throttle at lower speeds rather than WOT....the car runs better. Check engine light always comes on ~5 miles after I drive it. Shut the car off and restart....the light is off until you drive ~ 5 miles.

Recently it started bucking really badly at WOT. Now, I highly doubt the plugs are fouled. I mean from what the computer is telling me....the car is running lean. So, could this be detonation? Its rather violent. The wires are brand new magnecores. I only run 93 octane in my cars.

Also, what can cause this detonation? Running lean????
 
I had the car up on jack stands to change both upper control arms. While I was there I pulled the DS rear plug. It looked normal....was NOT wet or anything.....kinda whiteish if anything.

Pulled the codes again...and the only additional code was:

171-Fuel system at adaptive limits, Oxygen Sensor (HEGO) unable to switch (RIGHT SIDE)

Other Codes:

159-Mass Air Flow (MAF) higher or lower than expected during KOEO, KOER
171-Fuel system at adaptive limits, Oxygen Sensor (HEGO) unable to switch (RIGHT SIDE)
172-Lack of Oxygen Sensor (HEGO) switches, indicates lean (RIGHT SIDE)
186-Injector pulse width higher than expected
189-Fuel system at rich adaptive limit at part throttle, -system lean (LEFT SIDE)

I just don't know if the O2's could be bad causing all these codes and the driveability problem.....OR if something with the engine and componets (MAF, INJ, FPR, etc...) is still not right causing the codes and driveability problem...????????

Anyone????
 
oops..forgot to mention. I put the back seat and stereo system back in as soon as I got the car home. The only difference it made was the ARC is working again....and a little better sound from the stereo. I also noticed someone replace the original JBL woofer with a 6.5" JL woofer.

I'm even wondering if there could be a problem with the AFPR....I've been reading many people on here have problems with them. You might have had the right sampling tubes for the injectors but the fuel pressure regulator is fubarred. I mean that might explain why at times it seems to run fine and not at others. Who knows.....I think I'm going to replace both 02 sensors anyway....WTF....with 108K miles.....they need replaced.
 
Is that a smaller or larger speaker than the factory one? Not real sure about that stuff. Hopefully the O2 sensors will do something for ya!
Tad
 
I'm in desperate need of help ladies and gentlemen. I have absolutely no clue what is going on with this car. Any help is greatly needed and appreciated. At this point I have 6 choices:

1.) Put everything back to stock minus the engine porting.
2.) Pay someone who can tune cars $80/hr god only knows how many to get it running right.
3.) Sell it because I'm at the end of my rope and this car is the devil and I can't get any help..
4.) Run it into a tree and take the $1,200 (book value) from insurance.
5.) Sell it and completely lose my @ss.....buy another Subaru.
6.) Keep it and look at it...because I love the way it looks...just hate the way it runs and drives.

The car is running worse. I mean it has a new trick where it decides not to go at all.....like I'm giving it gas and it boosts but it wants to die. It has only done that a handful of times but I honestly did not think it was going to make it any of the times.

If I don't figure something out....SOON......look for it to be for sale after I do some work and get the title back from the state. It has a current 4/05 PA inspection although there is no way on gods earth it should have passed. I'll be replacing both front lower ball joints...hopefully before they fall out. I'm not sure if I'm going to go through the expense to get the exhaust done...until I know if I'm keeping it. I'm on the lookout for a 145mph speedometer since the odometer stopped at 108,058 on the original. The actual mileage is nearing 109,000 miles. Other than that....I'll probably replace the wiper blades and pay someone to adjust the sunroof...since it is out of adjustment and leaks. Although, if you shut it just right so it is tight....NO leaks.

I'm a patient person....I mean I'm nearing the end of a 5spd swap into my other Subaru SVX.....I just might not be patient enough to deal with this certain Super Coupe. I'm not saying it is a POS....I just might not have the patience to deal with it and the little issues.

Oh yeah, IMO, I think it is running rich....judging by the smell of the exhaust. Although the computer says it is running lean. It I thought it was pulling good vacuum but I was wrong. It seems to be around 15-16 ish at idle (which is very smooth), and 18-19ish when I let off the gas going down the road. The boost is still up there around 10-13 psi but it bucks so bad when I go WOT...I won't attempt it until the problem is fixed.
 
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Did you go back to the stock 30lb injectors and stock MAF? Maybe you need to reset the memory for the EEC.

Check for boost leaks. Use some hight temp RTV sealant on all the IC and tube flanges.

Pull a couple sparkplugs and see how they look.

I'd change the O2 sensors if your getting those codes.
 
The mods are in the first post of this thread. I still have the 42lb injectors and 75mm Pro-M MAF. I'm going to play around with the fuel pressure. It was reading 38-39ish at idle with the vac line hooked up. I'm going to research some old threads to see what everyone recommends for a modified engine and I will set accordingly.

I just don't want to start throwing parts at this car. I mean I guess I need someone familar with these engines to give me their opinion whether the 02 sensors COULD in fact be bad and making the engine run like ****....or if the the engine is just ****ed up and making the 02 sensors read off and set the CEL.

I'm reading that as long as I have the correct sampling tube for the injectors that I should not need a custom chip to make this thing run perfectly.
 
Ok, here are my findings.

I cranked the fuel pressure down to 39psi with the vac line removed. Oh boy was the car underpowered then and the bucking was worse. I then tried 42, 45, 48, with similar results. It seems to me at least that the higher the fuel pressure the better it runs but it still bucks. Strangest thing....I can feel the power but something is definitely holding it back. Also, lower fuel pressure made the CEL flash on and off at lower RPMs. I have it set to 50psi right now and it seems to be running about the same as before I played with it. I'm still getting the bucking when I get on it.

Codes are still:

Hard Faults:

159-MAF out of range

Memory Faults:

171-Right side 02 unable to switch.
172-Right side 02 sensor indicates lean condition.
186-Injector Pulse width higher than expected.
189-Adaptive fuel rich limit reached at part throttle, system lean, left side.

Can ANYONE help me interpret what these codes mean. Should I have to run the fuel pressure at 50+ psi with the modifications done?? The computer states the car is still running lean....so should I crank the fuel pressure up higher and see what results I get???????


HELP!!!
 
Hard Faults:

159-MAF out of range:

ur sensor is shot, replace it.

I say u replace ur MAF sensor first. Go to the junkyard and get one. see if it works.

Ur MAF sensor messes around with ur injectors and O2 sensors if it is dead.
 
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