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Hardtop FTW
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1,784 Posts
Discussion Starter · #1 · (Edited)
My mods:
- Bosche 110 By-Pass Valve
- ZEX Spark Plugs
- NGK Wires
- 2.5"-3" Downpipe
- 3" Cat-back Exhaust

Last november this car ran 14.7 with a minor boost leak and similar mods. Today my best time was 15.429. (And before you even think it, no; I'm not a bad driver. I can't be because it's automatic.) Needless to say I was quite unhappy. The whole night it never felt like the turbo was really spooling though it was nearly pegging the guage at 8psi. Earlier on, it had been misfiring in O/D while boosting (it's done this VERY slightly for some time now) at ~5 PSI going down the freeway, and on my way home from the track, it was doing it even more severely, esp. at low rpms under boost. The last time I had problems with a car misfiring under load at low rpms it was a Honda B18B1 (Integra LS non-VTEC) and the spark plug wires were toast. However, everything in the mod list above has been added less than 6 months (4,000 miles) ago, meaning in theory that my plugs are wires are perfect.

Another thing is that over the last couple tanks of gas, I have been lucky to see 200 miles per tank. I generally put about 13 gallons in, so assuming
I got lucky, 200 miles/13 gallons=15.3mpg... This also makes me very unhappy.

The way I see it, these symptoms are most likely to be caused by a poorly ignited mixture caused by bad spark plugs or wires, or running too rich, making it difficult for the mixture to ignite and burn properly. Now since my plugs and wires are new this leads me to believe that the a/f mixure is most likely too rich. (Which would also help explain my gross lack of economy)

Recently I had an intercooler pipe fail. The pipe leading from the turbo to the IC was baked and split where it connects to the turbo. Since this is my only car, I was forced to continue to drive it to work. (In my defense it only leaking under boost. Meaning that no unfiltered air entered the engine.) Obviously since the AFM was seeing lots of air pass by that was then just leaving the system through that tear in the intercooler pipe, it was running grossly rich. According to my friend, (speaking of Accord) I was pumping enough raw fuel out my exhaust to fuel a Honda for a considerable amount of time. To my knowledge, in extremely rich conditions where unburnt fuel goes out the exhaust, the O2 sensor can be fouled. A fouled sensor would not be able to correctly read the amount of oxygen in the exhaust and think it's running lean. The ECU compensates by adding fuel, and there you go! It's running grossly rich and my problems are addressed.

My questions for you guys:
-Is my understanding of a fouled oxygen sensor correct? Is my understanding of the rest correct?
-Does anybody else have another theory that I can look into?
-How can you tell if a sensor is fouled?

Thanks guys,
Collin

EDIT: 15.429 best time not 15.299
 

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what would jesus drift?
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987 Posts
i can tell you how to check to see if your o2 sensor is switching lean to rich..

with the check connector jumped (te1 & e1) copnnected, check the voltage at vf, .250 is 14.7 and a higher number is lean and a lower number is rich . if not it's the other way around, but is should switch 8 times in 10 seconds or soo..
lean ,rich,lean,rich,lean.. so on..

maybe some thing about running at 2500 rpm? , i dunno i'll search through my notes, pm me and i'll remember..
 

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Ludicrous speed! GO!
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during that time that you were running it rich, the plugs coulda been really fouled up. Their gaps might have increased from the misfires.

after you fixed your boost leak, you did fix it right? did you reset the ecu to see if it helps?
 

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Fix your Boost leak. also with this older car i think you cant expect much mpg out of it. plus with a turbo car it also has to do with your driving habits.
 

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After read this thread i did a lil research , and the mkII turbo is only supposed to run 15's out the door ? thats like what hondas run all day , i was diapionted what are some of yalls times bpu ? just curious


-fox
 

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mark3beeter said:
After read this thread i did a lil research , and the mkII turbo is only supposed to run 15's out the door ? thats like what hondas run all day , i was diapionted what are some of yalls times bpu ? just curious


-fox
It's almost 2x the weight of the civic though.
 

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1991 1JZ
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1,157 Posts
mark3beeter said:
After read this thread i did a lil research , and the mkII turbo is only supposed to run 15's out the door ? thats like what hondas run all day , i was diapionted what are some of yalls times bpu ? just curious


-fox
13.7 with a minor blown head gasket.
 

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My car had almost the same symptoms, check for boost leak. Even though your boost gauge is showing boost, it doesn't mean there isn't a leak. I had a really bad one and I fixed it and now everything is almost fine.
 

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Hardtop FTW
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1,784 Posts
Discussion Starter · #13 · (Edited)
I have fixed all my boost leaks and checked the whole system over. I have already replaced the damaged portion running from the turbo to the IC with hardpipes, and I am no longer hitting FC. I used to hit FC at 4-6psi, now it boosts happily up to 8psi with no problems and spools quickly. It would go higher if I had a boost controller. In other words, my problem is not boost leak related.

I have ZEX 3-point plugs. They are VERY beefy, and I do not believe that the gap can go out of spec. ZEX claims that they will never need to be adjusted.

I reset the ECU just before running my first pass.

Full timeslip info:

Reaction: .099
I1: 2.455
I2: 6.681
I3: 10.072
MPH (I3): 73.640

E.T.: 15.429
MPH: 92.446

Any other thoughts?

Thanks guys!

Collin
 

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Shop Tech All Around Auto
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510 Posts
Have you checked the coil pack? I see 'em go bad on Chevys all the time; don't know about on the Supra's though. What about a vacuum leak? Is your air filter clean? What's your fuel pressure like? A friend of mine had one in his shop that ran like crap. It wound up being the vacuum line from the air duct behind the mass air that runs down by the power steering pump. Easy way to check vacuum lines is to blow smoke through em. Find a shop that has a smoke machine, and ask em to test it. Oh yeah, and check the plug to the coil. Make sure all the wires are making good contact, and that both ends are clean and pretty, no corrosion. WHen you look in the end of the harness plug, all of the ends should be in the same place. Make sure one isn't pushed back. If there is one or two, gently push it back in from the harness end.
 

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resetting the ECU before the first pass is a problem as it's running in safe mode and relearning it's entire fuel curve

I don't trust those kinda plugs, I used em in my truck and they last longer, but properly gapped stock style plugs ran better...but not as long


but I'm thinking it's you resetting the ECU before you raced, every EFI car I've ever messed with ran like crap right after being reset, not wanting to idle, ect... until it learned and ran right...
 

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Always playing catch up
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well a) your 60' sucks, learn to brake boost! im a manual and i pulled a 1.997 on street tires on stock size.

b) check your vac, what is it at idle? should be 18-20~ish (warm)

c) also, check o2

d) as stated, its how you drive and where you drive, my car city does mid 18's for mpg in city/light highway, but it will do mid to high 21-22's if i pretty much go all highway

e) um, random guess, but maybe the stall converter took a crap and its slipping now?

<l><l>
 

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Hardtop FTW
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Discussion Starter · #18 ·
lagged said:
heh look at your MPH. check your compression. that motor has about had it IMO.
I hope not and seriously doubt it. Barely any oil consumption and clean ass oil (no blow-by) all the way until the next change beg to differ. I will however be checking my compression next time the plugs come out, which may be soon. The engine has been run on syn. oil all its life and doesn't smoke one bit, excusing one tiny puff at startup. Don't we all have baked valve stem seals? :)

I'm going to pick up a new bosch o2 sensor and see if I see any differences. The way I see it, if my mpg improves, I've paid for the fresh sensor after 2 tanks of gas. That and I'll know it's new.

As for the plugs, I hadn't heard anything bad about them before, but I will look into it.

I also really hope it's not a stall converter problem.

I was looking over the car last night and checked my timing, pulled the o2 sensor (it wasn't black at least and was rather clean looking), and I found one of my lines was a little loose, the vac line running to the bypass-valve. I replaced it about 2 hours ago but haven't really had a chance to beat on the car and see what happens.
 

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O2 sensor will make a HUGE difference if it's messed up

I went from 200 miles per tank to 300...
 

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Hardtop FTW
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Discussion Starter · #20 ·
Poodles said:
O2 sensor will make a HUGE difference if it's messed up

I went from 200 miles per tank to 300...
Thanks. I suspect it to be at least part of the problem. I ordered one about an hour ago and should have it early next week.
 
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