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Discussion Starter · #1 ·
I've been trying to figure out why I have a misfire, or lack of top end power like it use to. I tried swapping coils and plugs, fuel filter ect.

The car has had it's great moments of running great.

Today I checked out my Greddy BCC and checked the voltage and it was
4.2V. I decided to set it to 4.3V, since I have a 94.

I read an article about bypassing the Turbo Pressure Sensor to eliminate the cars Boost Cut, but it is supposed to be a bad way to do it. One bad problem is the fuel pump will stay at 9V, unless you do the 12V relay mod.

Anyways, the vacuum nipple on my TPS was capped off. Should I hook this up to
any vacuum hose? Reminder, this car has been running awesome for the last 10 months I have had this car, except for the last 3-4 weeks.

I also use to have an OBD1 code #42, VSS circuit. I think that's what it was.
I tried the speed sensor splice a few days ago and the car ran like it didn't have any problems anymore. Now about 50% of the time I get a lack of top end power, but not really a misfire. But, no more code 42.

So, should I be hooking up my TPS to a vacuum hose? It has ran great like this before, so the only think I can think of now is the 12V relay mod for the fuel pump has been done before, and maybe the relay or something for the fuel pump relay mod has gone bad.
 

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I really doubt the turbo pressure sensor is causing your missfire. But if you want to check it anyways, just cap off the vacuum hose and take it for a spin around the block. If it doesn't effect anything I would put it back.

Are you sure your sequential system is working properly? Maybe only one turbo is coming online causing you to have no top end power.
 

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Discussion Starter · #3 ·
I re-did most of my intercooler hoses recently, and checked very well, so no boost leaks.
My car still makes 1.3 bar. I can still crank it up to 1.4 or 1.5 bar if I want to.

I do however, hear a change in the turbo sound, and it sounds like I'm just starting to get the death whine. I have a good compression check, but I have noticed my car burns more oil and have some dark smoke coming out my exhaust sometimes now, and had some oil in my intercooler, but the intercooler has been on for years, so maybe it was slowly building up.

I'm thinking maybe one of my turbos is going bad and it is sending some oil into the engine, and maybe that is giving me a mis-fire or lack of power.

I'll hook of the turbo pressure sensor tomorrow and see how it does.
 

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Interested in an answer...
 

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Discussion Starter · #5 ·
I'm still trying find out what's wrong. I put new coils in and it ran like a demon for 1 day.
Then it acted up again. I have been doing too many things at the same time though, so I might have had multiple problems. I took my upper intake manifold off last week to put a fuel damper bypass hose and a fitting for a fuel pressure gauge, also to change the o-ring on the oil cooler, check the camshaft sensors, read the resistance on the OEM fuel injectors ect.. The new coils and I messed with my throttle position sensor and IACV. My idle has been funny the last couple days, so I'm trying to figure out if I didn't put a hose on good. I also just set-up my Throttle Position Sensor today, and checked my crankshaft sensor too.

Today on the way to work I saw I was making more boost than usual, about 1.45 bar on a BPU car, and it has hesistation at high engine load. Before going home I turned down the boost and got 1.3 bar and it didn't hesitate as bad. I played with the throttle position sensor some more and the car can do 0-60 like a demon, but in 3rd or 4th it hesitates under high engine load.

I think I got the throttle position sensor set just right, so I'll see how it does on the way to work tomorrow.

I already changed my plugs again last week with some NGK 4644 gapped to .028
I'm going to change all my vacuum hoses this week. I might change my O2 sensor next week.
Oh, and yesterday I noticed one of the nuts holding the upper intake manifold came loose and was about to fall off, I tightened that one up yesterday and it's still tight today.
I'm wondering if I have a vacuum leak somewhere. My boost gauge shows about -.65 bar . I think that's how you express it. My hand held vacuum gauge gave me a -18.5 inches of vacuum. I use to have -.7 bar of vacuum. Also, my car idles good sometimes and then the next minute it doesn't. I did the Seafoam thing in the intake manifold and it permanently raised the idle to 1,100 RPM, I thought maybe it freed something up. I adjusted the idle back down to around 700-750 RPM. And lastly, I looked over all my intercooler connections today and they are good.

I'll see if changing all the vacuum hoses does anything. I tried taking off the hose going to my BOV and it broke real easy and it was hard as a rock. I have a lot of hoses that are hard as
a rock, so maybe I will at least pick up some sort of benefit from new hoses. I guess if this doesn't work, I will be checking all the components to the turbo system. I plan on going single turbo in December or January, so I can remove all that stuff an eliminate those as a potential problem. I'll have a fuel pressure gauge in tomorrow night, so that can show me if the fuel pressure is OK. If that all don't work, I'd think I have a bad fuel injector.
 

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It sounds like you're losing spark... if the new coils came with new boots, then never mind what I said...

Although if you are using your old boots, then one or more has a crack or tear. Examine them closely, the cracks aren't noticable unless you kinda "squeeze" the boot.

Choritsu-shi
 

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I feel for you! I have had a misifre and clunking sound during idle for over 3yrs!!! Piss poor MPG (225 to a full tank), low idle 300-400, occassional stall. This all started after I washed the engine and took it out for a fast drive, I have original coils, 152XXX miles, no cracks, new boots, new lead wires to coils, new camshaft sensors,....to much money/time wasted throwing it at the Sup. I'm taking mine to FSR....I've given up.

Mine will boost fine and over boost if I keep the pedle down.

GL though!
 

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Discussion Starter · #8 ·
I noticed a trend. On the way to work today I didn't really get a chance to do some hard pulls because there was too much traffic. On the way home today the car ran the way it should.

I opened the hood and noticed the bullfrog sound. When my car ran great a couple days ago it had the bullfrog sound with the car running. Also, I get 21 inches of vacuum when the car runs good. When my car runs bad I only get about 18.5 inches of vacuum, a bad idle and no bullfrog sound.

I remember reading about the bullfrog sound, so now I have to look it up, and ask about it if I can't find the answer. I think whatever makes this bullfrog sound is the issue, maybe it's bad, or a hose or wire if there is one, going to it is bad.

My coils before were definitely bad, when I tested them off of the car half of them would shoot sparks from the stem area. And I had the clunking noise. I don't have the clunking noise now that I changed the coils.

If you disconnect a coil when the car is running, you will here a serious clunking noise.
With a bad coil you will here a clunk when it misfires.
 

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if your IACV valve is bent then you would get the bullfrog sound. It looks like one of your vacuum lines fell off or the actuator failed. then the boost pressure bent the IACV valve
 

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"test them off the car" do you mean you pulled them halfway out and saw spark ?
 

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Discussion Starter · #12 · (Edited)


this is the actuator i'm referring to


Thanks for the picture. Mine is very straight. I wanted to see the reed valve, so I took it off and it looks fine.


I think it looks fine, I never seen a reed valve, but now I seen some on Youtube.

I just applied pressure to the IACV and it opens the butterfly that is part of... I guess the IACV system. So the reed valve looks ok, and the IACV valve looks OK, now I will troubleshoot the IACV VSV later tonite.

I have one of the HKS Megaflow intakes which people say they hear the reed valve. But what I'm trying to figure out is why I only hear that noise when the car runs good, and I don't hear the noise when my car run has issues with high load hesitation. Also, when the car runs good I get 21 inches of vacuum and only 18.5 inches of vacuum when it runs bad. The hoses look OK, I use to have one of them come loose but I zip tied it. It will take me a couple days, but I will put on all new vacuum hoses each day until I do them all.
 

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Discussion Starter · #13 ·
"test them off the car" do you mean you pulled them halfway out and saw spark ?


I tested them off the car. My buddy let me borrow his set of coils. But some of his are bad too. I also put on all new clips to the coils, and some of the wire.
I took the looms and tape off of the coilpack wires and the wire looks good, except for a couple spots, which I changed those parts.

My car use to misfire and sometimes hesitate. Now it hesitates sometimes with no mis-fires. I notice with the cold weather the boost was up to 1.45 bar, which might have caused spark blow-out. It was running 1.4 bar today on the way home, but the car ran great.
 

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Ok that's good you at least fixed the wires. Mine were bad also so I took them all back to were they come up near the cam gears.
 

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Discussion Starter · #15 ·
I feel for you! I have had a misifre and clunking sound during idle for over 3yrs!!! Piss poor MPG (225 to a full tank), low idle 300-400, occassional stall. This all started after I washed the engine and took it out for a fast drive, I have original coils, 152XXX miles, no cracks, new boots, new lead wires to coils, new camshaft sensors,....to much money/time wasted throwing it at the Sup. I'm taking mine to FSR....I've given up.

Mine will boost fine and over boost if I keep the pedle down.

GL though!


Do you have any idea what your problem might be?
 

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I could only assume its something electrical..
 

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Japanese Tuning in Plain English

.....
My coils before were definitely bad, when I tested them off of the car half of them would shoot sparks from the stem area. And I had the clunking noise. I don't have the clunking noise now that I changed the coils.

If you disconnect a coil when the car is running, you will here a serious clunking noise.
With a bad coil you will here a clunk when it misfires.
Like I was saying..."It sounds like you're losing spark..." Did you replace your coil boots? or are you using your old boots?


My car use to misfire and sometimes hesitate. Now it hesitates sometimes with no mis-fires. I notice with the cold weather the boost was up to 1.45 bar, which might have caused spark blow-out. It was running 1.4 bar today on the way home, but the car ran great.
No, I don't think you had spark blow-out. In your case... the increased pressure was too great for the spark plugs to ignite... therefore the spark finds an easier route and creates "paths" to ground... which was going out the stem or boots of your coils to the cylinder head.

Choritsu-shi
 

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Discussion Starter · #19 · (Edited)
I have new everything for the coil packs, new boot, clips, and I looked and replaced some of the wire.

I put a new boost gauge in last night and put it somewhere I could actually see it well.
My BPU is boosting way too much. I was getting about 22-23 PSI.
I think I had multiple problems. I fixed the coil pack issue. Now I been messing with my throttle position sensor and I think I need to set that right now. If the car is idling, and I'm under the hood and open the throttle a little but quickly, the engine stumbles.

My wastegate has never seemed to do much. When I had a Greddy Profec 2, it didn't seem to control boost very well, now I have a Hallman Pro manual boost controller and it still doesn't seem to do much, I know I have the hoses on correct and the hoses are rather new.
I'm going to play with the boost today and try to get it to run on 18PSI and see what happens.

Also last night I finished installing a fuel pressure gauge and it idles at 53PSI and doesn't change at all when driving. The fuel system holds pressure for a long time after I turn the car off though. I noticed a previous owner did the 12V relay mod to the fuel pump. I might undo that. Last week I had the upper intake manifold off and I bypassed the fuel dampener.

I'm thinking if I can keep the boost to 18PSI it will run good.


Edit:..... Never mind on the fuel pressure being 53PSI. I used a more reliable gauge and got 43PSI.
 
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