Lost My Boost
 

Drove to work yesterday and the car ran fine. On the way home I pulled out to pass someone and the car wouldn't go. It won't rev above 4000 and doesn't even want to go that high. Boost gauge never goes above 0. I was able to drive it home at reduced power. Looked under the hood and everythig looked O.K. but it was hot and I didn't get a chance to work on it last night.

Any ideas where I should start looking when I get home today? I drove the other car so the Miata will be cool enough to work on as soon as I get home.

Thanx.

Look for loose or broken piping first.

All intake piping is secure and un-broken. No broken couplers that I can see from the visual inspection I did last night. I will check the undersides when I get home.

check to be sure the couplers are securly attached. that's most likely your problem

+1 on the check your couplers.

Sometimes, it's just a tear near one of the pulleys b/c the pulley can touch the coupler briefly with engine movement. You won't see the tear sometimes, but if you remove the coupler, you'll see a crack that would open under boost. Also, once I had a loose coupler that leak under boost but on quick inspection of the pipes, everything looked like it was still together as nothing was separated.

All hoses, pipes and connections are good. A friend of mine, a local turbo guru, thought it might be a frozen impeller shaft but that wasn't it either. The general consensus currently is, constipated kitty (plugged cat). I'll check into that this weekend.

you have a failed coupler....

Local turbo guru in Orlando? Who?

Sounds like a massive leak. If it weren't for the artificial 4000rpm rev limit I would suggest a wastegate failure.

Pressure test the system, a visual isn't 100%. If you have a diverter/blow off valve that could be the problem.

Guy I work with. He's been building turbo systems for about 20 years, mostly Datsun / Nissan. Has a small shop in Merrit Island where he only takes in jobs that interest him.

check for any broken piping connected to intercooler...and make sure all the couplers are attatched and screwed down well. what is your vaccumm at idle?

Long as he has no affiliation with ISP... or had. I don't think that they are around any more.

I'm in Orlando is why I ask, and most people here have their heads so far up their asses they are looking out of their own mouths...

speedracer, Vacuum at idle is 20. The intercooler has not been installed yet. The reason I'm leaning away from it being a coupler is that the AFR doesn't go to full rich like it has any other time I've had coupler problems. I will pull all couplers and piping as soon as I'm sure it's not the cat. I haven't had time to work on it this week. Life happens.

PAT!, I don't think he has or ever had any affiliation with ISP.

What other mods do you have? I mentioned a valve, if it is recirc and it has failed it can kill boost without technically being a leak... don't know what would happen to the AF in the case. What are you using to tell that the AF isn't going rich?

Have you checked the wastegate yet? Could have failed in a number of ways.

BOV is vented to atmosphere. If the waste gate was stuck closed I would expect to see an overboost condition. If stuck open the revs would not be limited and the engine should act as if normaly asperated.

Narrow band O2 sensor with gauge. It behaved normaly, bouncing between lean and stoic (sp?) while driving. When I've had coupler failures or blow offs in the past it has gone to full rich if the engine kept running. Such as when this happened.
https://www.miataturbo.net/forums/vb...etimage&id=426

See above.

Do you have a cat? Could be clogged.

What other mods? Something that could be effecting timing? Something that alters the rev limiter? Something that could affect fuel?

Other than that all I can think of is something physically limiting the amount of air coming into the motor...

Has anyone seen an AFM fail and cause the rev limit issue?

I've seen worn (gap too large) spark plugs cause what seems to be a rev-limited misfire condition, but it usually happens at higher boost levels and not at zero boost as mentioned in a previous post.

fuel pump or clogged fuel pump sock filter. i had IDENTICAL symptoms with a clogged sock filter (nasty rusted gas tank)

Check the accordian.

It was the cat! I was going to hollow it out but it had been replaced once with a generic one and was welded on both ends. I took it to a muffler shop and they put in another generic one, runs fine now. Hopefully in the fall, new down pipe, high flow cat and cat back exaust.

Thanx everybody for your comments and suggestions,
Pete

Cool:bigtu: