davesan1

iTrader: (4)

After multiple boost problems I decided to systematically check out all (or most of) the multiple suspect causes, with the great help of all the "how to" links in this forum.

Car is early 1993 model MK III, 100% stock, CA emission control. New engine at 104K miles. Replacement unfortunately done by someone not so familiar with all the tubes, etc. Repeated returns to replacement shop to no avail.

I've had it, so I decided to go it alone! Started this last weekend

Installed a boost gauge. No surprise, boost pressures, RPM correlation etc, bore no relation to normal readings. Found and fixed a couple of misplaced vacuum pipes and a leaking 1" hose from the primary turbo. Definite improvement so far, but still no boost at low RPM. Checked the Air Bypass Valve and, (though maybe not directly relevant to lack of boost at low RPM), the Charge Relief Valve. In both cases, with anything above about 5 PSI pressure applied, the valves do not fully seal when "off" (no vacuum applied on vacuum actuator port). They clearly open more when vacuum is applied to the actuator port, but the lack of seal when "off" is certainly a potential source of boost leakage.

So, my questions..

1) Is this a common problem?

2) Replacements are extremely expensive! Anyone know of an alternative or aftermarket type replacement?

I want to check the mysterious (hidden) Vacuum chamber's operation. I located what I believe is its feed via a check valve from the inlet manifold, but it is difficult to see and access where it goes (so far) after the check valve. Pulling the pipe off at the manifold I can apply and sustain a vacuum but my suspicion is that it is not pulling air out of a tank because my pump "caps out" after a couple of strokes, suggesting that it is only evacuating a small volume, (like just a capped vacuum pipe, for example). Next step is to pull off the check valve and see if it's working, but difficult access + a slightly brittle vacuum hose in that area is making me hesitate initially in case there is an easier way to check it out. So, does anyone know if there is any other "readily accessible" tube that is directly connected to the vacuum tank? If so, I can check that it does (or does not) actually evacuate when I pump vacuum from the manifold end of the check valve, and that it subsequently holds the vacuum.

Note I have all the vacuum pipe diagrams downloaded and eventually can probably track down a convenient point, but the combined experience of the forum can probably save me a lot of time. Also, there is some confusion, in that I have a copy of AutoSport Race Tech's most useful document "Trouble shooting Sequential Turbocharger Problems" and it identifies the location of the above mentioned check valve as "the only check valve between the firewall and the throttle body.” On mine, and per the color vacuum pipe diagram, the check valve appears to come from the other side of the manifold (nearest the front of the car), so I now wonder now if I have identified the correct vacuum tube from the manifold. Can anybody confirm whether the location stated in the document is correct or otherwise?

Thanks

Next weekend I attack the various actuators on the turbo itself. Say tuned, it's a MK II, I know it will be eventful!!

DaleClark

iTrader: (55)

Sounds like you're headed in the right direction. A car that's been monkeyed with by someone who's unsure of what they're doing can be a chore to troubleshoot!

Few things -

First off, the car is a 3rd Gen. MKIII is what the Supra guys call the late '80s Supra . FD or FD3S will also suffice, and Series 6 if you wanna get Aussie .

The best bet for the leaky BOV's are finding good used ones. People routinely buy new BOV's, ditch them going single turbo, etc. so finding good used ones cheap shouldn't be a problem.

What kind of boost pattern are you currently getting?

Also, check all the intercooler pipes for leaks. The rubber connector from the Y-pipe to the crossover pipe VERY commonly splits and leaks, and causes all KINDS of problems. If you have boost leaks, you'll just chase your tail with vacuum lines and solenoids.

I think it's Derek Vanditmars site that has the very comprehensive step-by-step on turbo troubleshooting - it should be linked to off of scuderiaciriani.com. That's an EXCELLENT source.

Also, don't forget to change spark plugs and do other tuneup type things. Bad plugs can make a car run horribly!

Good luck,
Dale

davesan1

iTrader: (4)

Dale -

Thanks for the input.

OK, 3rd. Gen it is!

No success yet in finding used BOVs. I'm probably going to have to bite the bullet and buy new.


Boost pattern a little difficult to accurately define as I have not yet mounted the gauge so it is lying on the floor! However, looking at it from there, seems like there is no boost at all until just after 3000 RPM. Seems to get up to 10 psi after that, but starts to drop off at around 5000 RPM, down to 5 psi or less

Also, I now notice that highest boost comes with only partial throttle. When floored and held, boost seems to come on later, (higher RPM), and not as high boost (around 4 psi) as with just partial accelerator.

All sounds odd. However, we should take into account that there may be more vaccum/pressure or even electrical (solenoid) misconnections as a result of the non-expert engine replacement. So far I've only tackled the easy ones. The turbo actuators/ wastegate actuator, etc are scheduled for this weekend. I'm leaving the stuff underneath the inlet manifold until last, hoping that I don't have to go that far.

Already checked all the intercooler pipes and they are all good (these had often been a problem in the past, pre the new engine, when the turbo boost was otherwise behaving well). During that time I relaced almost all the pipes over a period of time and added new/better clamps, etc).

Yep, I have a copy of Derek's stuff - extremely useful. It's great to find that there is such a terrific knowledge base our there these days. When I first bought the car (1993!) and for several years thereafter, nobody seemed to know anything - including Mazda. Regretably, this latter item is even worse today!

Good idea about the rest of the tune up

Thanks again

DaleClark

iTrader: (55)

Post up in the Wanted section of this forum, and also check http://www.thepartstrader.com - they do turn up pretty frequently. Shoot, I think I actually have some somewhere, but they're likely long gone by now!

Dale