slow building boost
 

guys,

Got a problem on my FD recently whereby boost builds very slowly - almost like its spinning up both turbos at once.

Saw a thread a while ago with a guy with a similar issue, and it was found that all solenoids were working ok, but one had a weak spring causing it to not be able to close quickly, causing major turbo lag.

I think i have the same problem...that or a totally failed solenoid. Sometimes its fine, sometimes its not. Car is totally standard bar air filters, defi gauges and lots of TLC.

Anyone have any ideas?

thanks

Bob

Sounds like a solenoid problem to me. I would just take them all out and test them all, hot and cold.

Does it build slowly on the primary? How much pressure are you seeing at 3,000/3,500/4,000 RPM?

Yes it boosts slow on the primary. Boost is normal, it just takes a while to come on. E.g at2.5krpm in 3rd gear nailing it, full boost doesnt build till about 4k rpm. Its not quite that severe, but its noticeable. At 3.5k in 5th, boost normally shoots straight up to 10 in around a second or so, but when i have the problem, it takes more like 3 or 4 seconds. Its intermittent... havent tested yet whether its a problem after a drop from secondary boost or what yet though. ( i remember one guy that had this problem only after he boosted past transition and then coasted down to before transition. I havent done this test yet)

I think sticking turbo control solenoids are the most common reason for laggy boost like this.

I remember you did a full rats nest job - did you replace or test any of the solenoids then?

Dave

i did the "click" test on them, but thats it. Dont have a mityvac and had no reason to suspect that they werent functioning correctly.

Oh well, at least ive got the experience to pull it all off again and test them properly this time :P

What you say makes sense too looking at the diagram and referring to my memory of previous posts on this subject....pressure tank fills with boost, pressurised. After hitting secondary, the boost in the pressure tank holds the solenoid open and actuates the secondary turbo solenoid, so both turbos have to spin up at once.

I wonder if there is any way to reverse the way it works so that rather than holding the solenoid open, the boost forces it closed. Maybe then they wouldnt wear out...

Anyone know how much a new solenoid is from mazda?

$55/ea from Mazda.

The click test is fine, but it's better if you have a vacuum pump to give it some resistance like reality. The turbo control solenoids are more likely to stick like this. I don't think re-routing it would work too well - a pressure regulator might help to allow you to run the vacuum and pressure systems at the minimum necessary level. It doesn't need a full 20" Hg / 12psi to operate, although it is usually at that level.

Dave

well f you check all those pain in the but solinoids and there in good shape and the hoses are all attached fine then start looking at your exhaust system could have a cloged pre cat or main cat. i didnt read your mods but im thinking your all stock rite?

A clogged cat doesnt' cause intermittent boost problems. Clogged is clogged.

Dave

Thinking about it, my spark plugs do have about 3k miles. Do you think this could be the cause? it doesnt seem to be missing but i know the trailing spark is barely noticeable if its not firing, does this make a large difference?

I had a problem where my boost would come on about 600RPM late (10PSI @ ~3,600RPM). I messed with a lot of things, then I adjusted the pre-control actuator arm so that the arm was a bit shorter. Apparently, the actuator was a tad too long (not sure how it got longer, really), which caused the pre-control door to be slightly cracked open.

The actuator arm may be seized with all the heat cycling it has seen (at least in my case it was), which will require removal and a vice for you to adjust it. IM me on aim if you need more details. I also had a thread on it, if you wish to search for it. Happy hunting!:)