Cool vid, might be something fun to tackle some weekend on another car. Just not on a friend's car when I've never done it before!
Cool vid, might be something fun to tackle some weekend on another car. Just not on a friend's car when I've never done it before!
Good point!
Sounds like the perfect time to me!!!
Supra findings:
The intake hose came today and I put it in. Much easier than the MR2 Turbo, although it took more hulk wrestling, being more rigid than the MR2 hose.
This didn't fix the problem.I wasn't really expecting it to.
During my test drive late tonight with no one around, for the first time I got a decent sense of what the car is actually doing under boost. Report I got from the owner was the 2nd turbo wasn't coming on properly or reliably. So I wasn't expecting to experience breakup during high boost -- the type of sudden breakup that makes me think ignition. The hastily-installed mechanical boost gauge for diagnostic purposes has no lights for night driving, and my phone won't record video with the flashlight on, so meh. But the gauge A) reads as high as 13-14psi when OEM spec should be 11.6, and B) flutters. Low amplitude (like 0.5psi), high frequency flutter. There is a slight kink in the line -- would this produce an erroneous pressure reading during boost, or a flutter during boost? Vacuum seems in spec.
Now here's the other interesting thing. If I keep the car to half throttle it goes faster and doesn't break up near as much if at all, compared to flooring it. Same RPM range. So then I thought maybe the TC pre-throttle-body might be doing something funky at WOT. I tried to turn off TC but couldn't figure it out.
It's OBD1. Shouldn't the car at least report a general misfire if it's really an ignition breakup problem? I don't think OBD1 can narrow down the cylinder. Also, the fact the breakup was throttle position based and not RPM/boost based, seems weird. The boost gauge reads the same (more or less) when I'm full throttle or half throttle, but the car breaks up / hesitates at >50% throttle.
I'll throw the two VSVs in that I have here, and do some more research as I have time.
Targa top rattle repair attempt today. Simply removing the top is quite a bit more involved than MR2 T-tops. On those you just undo a latch and pull the top out. Easy peasy. The Supra has a locking allen head, plus four allen bolts. The car came with a ratcheting allen tool from Toyota when new (this car still has it). Significantly more awkward.
Removing the headliner from the targa roof was a big pain. The normal way to do it is to destroy the weatherstripping seal and replace it. Yeah, no. I got it done but it took a while. Anyway, that was to get to the rear latch bolts inside which very commonly are loose and cause the rattle. I was all set with loctite and everything. But they're fine!
The other reason to get inside was, the allen head for the lock mechanism is pretty well rounded out. Not even a torx worked. I randomy found something the right size and fashioned an extension and wrench onto it to get the lock undone. McGyver moment there.
The problem is, I can't see any way to replace this 'bolt' without replacing the entire latch assembly. Which I just looked up. It's $80. It's such a simple latch!
So I'm kindof not sure where to go next. I'll probably drive around with the top on but headliner out next time I test the car, and maybe that'll help me narrow down the rattle.
Check it broskis:
https://photos.app.goo.gl/uJACv5YzJLQvy3Eo1
Slot it.
Whoomah!
Glad cool cars are still flocking around you ;-) Great to hear about the AW11, too. Did you have a pic of that car exiting the Corkscrew, leading a light blue Viper?
'Breakup' under high boost could be the fuel pump not keeping up (either the pump itself or the fuel filter being blocked) ? Or, the ignition wires all being cooked and not giving a strong spark? I've heard that boost can 'wash out' a weak spark - e.g. on FD:UK forum "Mapping did not go to plan, anything over 0.6 bar of boost caused the spark plugs to be washed out and create a missfire (with a lot of flame) ... Over the summer I replaced the coils, leads and plugs plus wired a direct feed to the coils just to be sure. Thankfully this paid off "
The FD has a similar sequential twin turbo system, which is famously failure-prone.
Problem 1 is vacuum leaks - either pipes, or the plastic bits that join them, or the plastic pressure accumulator chamber. People often replace rubber pipes with silicone. Leaks can cause intermittent 2nd turbo operation, or a bad transition, or it works when you first hit 2nd turbo, but when you lift and re-apply throttle it doesn't come back in.
Once you fix all the leaks, you then have problems with your solenoids - the electric motor-y things that move flaps and so on. Often they fail such that they stop working when hot.
After that, you're back to cracks in the large cast-iron housing that holds the two turbos, or the turbos themselves can fail.
I'm not sure how similar the Supra is.
Last edited by samoht; November 18th, 2017 at 04:42 AM.
I finded something of interest in the Supra. Two vacuum lines were switched at the Intake Air Control Valve VSV, which provides a key role in secondary turbo operation.
In switching them back I broke a nipple off the old VSV.It had been epoxied back together previously, and tenuously. A small piece must have been missing at the prior break already because the nipple was askew a bit. I want to epoxy it back together again and also find a more permanent replacement. The Toyota part is $75 (wow), Dorman has one that looks like it is the same even down to the plug shape. Dorman doesn't list any parts for Supras on their web site, but a VSV is a pretty simple thing...
What's a good glue/epoxy for little plastic pieces?
I'm still thinking there could be a weak spark under boost given the behavior of the car, but I'll go down this cheaper vacuum line road first.
I have an idea/strategy for the rounded out allen head in the targa latch mechanism too. We'll see if I can pull it off...
Must be another car you're thinking of. I never took any of my own cars on track at Laguna. Too many walls.Originally Posted by samoht
Good thought on the fuel filter, too! I looked it up and it's not as easy to change as the 300ZX filters. The main issue with the Supra is the flare nut which can strip. Then you have to buy a $200 fuel line too.
The MKIV Supra TT is a coil-on-plug ignition. From my reading, it's usually the wiring at the coil packs or poorly sealed plugs that cause issues. The tricky bit is it's usually not possible to test for a bad coil when the car is at rest, so you just replace them with known good ones and see if that fixes the problem.
But yeah, weak spark under boost seems plausible. If the VSV repair and properly routed lines doesn't solve anything, I'll check the plugs and their gap. I'm told they were replaced recently.
Slow but steady progress over the past few days.
The breakup under boost seems to have been solved. I ordered one new coil and put it in #6, and it was better but still did it, then I moved it to #5, and there's no breakup at all. Coincidence? Got lucky? Actual problem solved? Who knows!
Boost is still not boostitating correctly, and I'm in the process of narrowing that down. What happens is inconsistent so my thought at the moment is leaning towards a sticky actuator, or maybe even a sticky VSV. I've bypassed two VSVs to put the car into what they call "True Twin" mode, where both turbos spool up simultaneously instead of one handing off to the other via the complex system. On my next test drive this may or may not be telling as to where the problem lies.
The boost gauge also reads 27in/hg of vacuum at idle which is really high. I don't think it can be trusted for anything other than if something changes. Absolute values are no good. It was a $10 gauge, guess you can't expect much.
How about this PCV hose? It appears semi-collapsed at a bend. When I rev the engine a bit, it expands just slightly. This appears to be a very thin walled hose, likely not stock. In my searching I haven't figured out yet if this is a problem or not.
Also, I fixed the allen head for the targa latch. I used SteelStick by JB Weld. It's an epoxy putty, almost like clay. Because it's less like a liquid I was able to put it in the allen head, stick in a next size smaller allen key for a second to give it a 6-sided shape that it more or less kept, and then after it cured, file file file to carefully enlarge the six sides to fit the proper size allen key. It was a bit tedious but I did a half hour each day and it works.
Driving around with the top off on a 75F autumn day is excellent.
Hmm, the True Twin conversion hasn't stopped the boost fluctuations. Which, actually, might not be boost fluctuation at all. Hard to tell when the boost gauge can't be trusted. The needle vibrates only at high boost, all other times it's smooth. Don't know whether to read anything into that or not. It no longer feels like a quick harsh cutout or stumble, the variance in power feels smoother since a couple days ago. Going to have to do some more thinking.
It's actually kind of cool in town this way, as the exhaust flapper is permanently open so you hear more good noises at low revs.
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