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Discussion Starter #1
I have a 94TT that's BPU, though with Kelford T202C cams (264/272), SAFC/AVC-R. Recently though I've noticed a lot of grimy soot collecting on the rear bumper, both near the exhaust as well as the other side. Just had it detailed, and the rear was grimed up noticeably by the time I got home.

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Tuning seems OK, sounds and acts the same. AFR is normal, high teens at idle, down to 11-12 under boost. Cams give it a nice lumpy idle. Exhaust is a 3.75" with a Random-Tech cat (all of about 22 years old now)

A while back the rear hoses that connect the pipe-tree to the pressure tank gave out, so I have it in TTC mode, with the EGCV and IACV both wired open. I haven't had a chance to check that the wiring is still holding the valves open as fully as when I put them on. Under boost there's a whistle, so if that's not turbo #2 beginning to go, then I'm guessing one of the valves has slipped a bit. Boost feels normal though, hitting the max that the AVC-R is set for.

Any ideas ? What should I look for ? The sooty grime looks like it's running way rich, but AFRs don't indicate that.
 

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I dont think there is anything to worry about there :)

Mine ends up like that after every drive, and I think its just road dirt being thrown up off the rear tyres and sitting on the lower rear quarter panel, and bumper/bar.
 

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Hopefully not. It's definitely not just road dirt - it only collects on the rear portions there. And it's pure black sooty grime. Feels somewhat oily.
 

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Feels somewhat oily.
Oh, that bit of info changes things a bit.

For what its worth, my car, which is also 3L2, collects the majority of its visible dirt/dust on the rear behind the wheels. At a a rough estimate, I would say that there is 90% more dirt in this area, than anywhere further forward than the rear wheels.
 

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Sounds like your turbo's bearing is going bad. With the motor warmed up, car parked, do a WOT burst to near redline. See if you get smoke out the back when you let off the gas. If that happens, you need to replace the turbo. You won't see the smoke when driving, and it's building up behind the car and getting on the bumper due to vacuum behind the car.
 

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It's the cams. I get a rich exhaust smell with the GSC S1's - so much so that I can't have the driver's window down at a light. But the A/F ratio reads perfect in all situations. Gas mileage is worse with the aggressive cams.

However, with all the cams I have had, I always had soot around on the rear bumper near the exhaust pipe. Really noticeable on a white car, lol!

Al
 

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I have the same , without a cat, and straight through pipe, tuning always makes the fuel run rich... you will see it on and off, nothing to worry about. BTW, my turbos are both brand new, so its not from the CHRA leaking or anything like that
 

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Do you have any smoke coming out of the exhaust? THere is no reason to have build up like that unless you are running very rich under idle or have an oil leak. That is a low pressure area at the rear of the car. Most exhaust is clean and won't cover your car with soot. Yours is not so either it's running very rich and your O2 sensor is providing a false reading (my guess is this is what is happening) or you have an oil leak and the oil is coating your rear bumper/fenders and then dirt is sticking to the bumper.

My recommendation is to get a new O2 sensor and see how that works out. Either that or look for an oil leak/blow by that would allow a lot of oil to pass through the exhaust.

Steve
 

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Discussion Starter #9
I've definitely noticed the drop in MPG with the Kelfords. Went from a good 240 miles to the tank down to around 200, though the last couple tanks have been below 200. I have an old 14Point7 wideband in there, and as I say, AFRs are good - idle is around 18 mostly.

Actually, I'm going to use this as the wife-excuse to go single with an FSR Street Fighter kit.

But honey, it would cost the same to get the twins refurbished and they would still be 25 years old. So I have to get it, don't you see ?
Already have the Haltech 2500 and VVTi head and Sard 800cc injectors ... Was originally just going to do the VVTi head/injectors and Haltech. But the siren song of single is calling ...
 

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Boost Junkie
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I've definitely noticed the drop in MPG with the Kelfords. Went from a good 240 miles to the tank down to around 200, though the last couple tanks have been below 200. I have an old 14Point7 wideband in there, and as I say, AFRs are good - idle is around 18 mostly.

Actually, I'm going to use this as the wife-excuse to go single with an FSR Street Fighter kit.



Already have the Haltech 2500 and VVTi head and Sard 800cc injectors ... Was originally just going to do the VVTi head/injectors and Haltech. But the siren song of single is calling ...
When was the last time you replaced your wideband? They do fail over time, especially if you've ever ran leaded race fuel. When they start to fail they start to read lean, which will cause the car to add more fuel.....they keep reading leaner and leaner, which means more and more fuel, and eventually they just fail and stay pegged at full lean (20.0/1 if you have a display). I've had it happen several times back in the day before E85 and flex fuel. You definitely have a problem if you have that much soot in the rear of the car.

Steve
 

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Discussion Starter #11
Hrm - that WB has been in there for years and years. At least 10 years. Bought from 14point7.com back in 2010 I think. I think you're on to something ... it's running silly rich now, and mpg has gone further down.

Interestingly, the display still changes as expected, reacting to conditions just as normal. You're saying that they can fail lean across their range ?
 

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These cars do tend to get black dust on the rear of the car - you especially notice it on a white car. Found this out when I first got the car and tried to dry it off with a short trip around the block like I had with my other cars. It had dust on it from a 5-min drive.

Personally, I don't think there is an issue with the OP's car. Maybe running a little rich from the cams, but I don't think you can do much there. My A/F ratios are also perfect, but I get a little more soot with the cams. But throw a new wideband o2 on there and report back, it's not our money, lol!

Al
 

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Why do you have cams on a car being tuned with an SAFC? I know that sounds like I'm being a b-hole but I'm serious.... you need a proper tuning system on your car. If you're blowing rich enough to put soot on your car like that then your "tune" is garbage.... which is expected with piggy back anything.

In before all the naysayers come on talking about the budget shit tunes they ran in the 90s on piggy backs and about how their car hauled ass.
 

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If you're using an SAFC you need to take more fuel out at idle.

Steve
 

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In before all the naysayers come on talking about the budget shit tunes they ran in the 90s on piggy backs and about how their car hauled ass.
LOL. Didn't even notice the SAFC mention in the OP. Didn't think people still used them.

Anyway, OP did you try out what I mentioned earlier in the thread just to rule out a bad turbo bearing? Might need someone to stand behind the car to see if there is smoke when you let off the gas.
 

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Discussion Starter #18
Heh, yeah, it's currently old-school. I do have a Haltech Elite 2500 and 800cc injectors ready on the shelf, and an FSR Street Fighter single setup coming soon. I had to do the valve-stem seals a while back, so dropped the cams in while it was open. Why not ? I was expecting things to be a bit off with the cams, but not quite that drastic.

It's too damn cold work in an unheated garage right now, so waiting till it warms up a bit to put on the VVTi head, FSR, 2500, etc. But I do take it out on a clear day.
 
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