Ebmessier
Ebmessier
7/17/20 2:37 p.m.

I have an NB Miata with FMII turbo. Recently acquired from the owner who added the FM turbo. Strictly a track car.  Last 2 events, road Atlanta and Pitt race, same problem happened.  Both events were 2 days. In each case, on the last session of the second day, and at no other time, the turbo would cut out under load (mostly uphill) and otherwise run fine.  When the turbo cuts out the gauge jumps and the car bucks.  No stall and it runs ok under reduced throttle.    I'm thinking loose ground wire but nothing seems out of place.  Odd that for both track weekends Saturday was 100% fine, but the last run of the day Sunday in both weekends had the turbo cut out problem.  If it was heat soak (it was hot both weekends) seems to me it would have been a problem earlier in the day or in day 1 when it was even hotter). 
 

Anyone with any thoughts?  Did searches and didn't really find anything on point. 
 

Help is very much appreciated.  

BoxheadTim (Forum Supporter)
BoxheadTim (Forum Supporter) GRM+ Memberand MegaDork
7/17/20 2:42 p.m.

Which gauge jumps? The boost gauge? In which direction?

bmw88rider (Forum Supporter)
bmw88rider (Forum Supporter) GRM+ Memberand UltraDork
7/17/20 2:44 p.m.

When you say cut out. Do you mean no boost or the car just loses power? 

 

If no boost, is there signs of an exhaust leak at the turbo mounting flange? First thoughts are the mounting studs are stretching and causing a leak. 

Ebmessier
Ebmessier New Reader
7/17/20 3:03 p.m.

In reply to bmw88rider (Forum Supporter) :

Looses boost, runs at "no boost" reduced power.  Bucks a little from the turbo cutting out.  
 

Would the exhaust leak have that kind of intermittent impact?  Car ran on track on Sunday under full load for about 2 hours (4 30 min sessions] before showing this problem, after running 2-3 hours on track the previous day with no problem.  But I will certainly check the tightness of the bolts from exhaust manifold to turbo.  

Ebmessier
Ebmessier New Reader
7/17/20 3:04 p.m.

In reply to BoxheadTim (Forum Supporter) :

Yes, boost gauge just to vacuum.  Usually runs around 10 psi of boost but when this problem appears it gives no boost and jumps hard to vacuum causing a little bucking in the car.  

BoxheadTim (Forum Supporter)
BoxheadTim (Forum Supporter) GRM+ Memberand MegaDork
7/17/20 3:12 p.m.

I'm pretty sure this is not an electrical problem - that all very much points to the turbo itself playing up.

Is that usually happening under load?

What do you use for boost control?

If it was me I'd probably also pull the intake pipe off the turbo and check for axial play, just in case.

morello159
morello159 Reader
7/17/20 3:18 p.m.

VVT car? If so, maybe try replacing your cam angle sensor. I had similar issues with my car - when that sensor fails, it shows up under heavy load when it's hot. Any data log of it happening? 

I dont see a turbo issue causing it to buck once and otherwise run fine... sounds to me like boost cut, AFR safety, sensor issue... 

Ebmessier
Ebmessier New Reader
7/17/20 3:19 p.m.

In reply to BoxheadTim (Forum Supporter) :

This only happens under load and it only happens at the very end of a track weekend with about 3 hours of total track time each event.  
 

im new to the turbo world so not familiar with the details of the boost control, but it's a standard flyin Miata II kit so however that comes is how the car is set.  
 

I had Joe from Corsa Crew check the turbo out at road Atlanta and he said it mechanically was sound.  

Ebmessier
Ebmessier New Reader
7/17/20 3:21 p.m.

In reply to morello159 :

No data log, not sure if the NB Miata has VVT but I don't think so, but sounds like this problem is similar.  Was thinking IAT ground but it looks ok.

BoxheadTim (Forum Supporter)
BoxheadTim (Forum Supporter) GRM+ Memberand MegaDork
7/17/20 3:24 p.m.

Well, if the turbo checks out that's good news.

IIRC VVT is 2001 onwards.

Keith Tanner
Keith Tanner GRM+ Memberand MegaDork
7/17/20 3:34 p.m.

What ECU? The FM II came with one of three for that chassis, and some people play a little loose with the nomenclature and will lump any FM turbo hardware regardless of ECU under "FM II".

This is not a problem with the turbocharger. I'm thinking you're potentially hitting a boost cut of some sort or you're getting an interrupted cam signal. The cam sensor is right on top of the intake cam, if it's going bad or has a wiring problem then it could cause this sort of problem.

Any chance of a datalog of the problem occurring?

Ebmessier
Ebmessier New Reader
7/17/20 4:42 p.m.

In reply to Keith Tanner :

According to receipt seller provided with docs, says FM 221 pro ECU.  
 

I don't have any data unfortunately.  

Keith Tanner
Keith Tanner GRM+ Memberand MegaDork
7/17/20 5:12 p.m.

Email keith@flyinmiata.com with the name on the receipts, I'll take a look at the spec.

codrus (Forum Supporter)
codrus (Forum Supporter) GRM+ Memberand UberDork
7/17/20 5:31 p.m.
Keith Tanner said:

I'm thinking you're potentially hitting a boost cut of some sort or you're getting an interrupted cam signal. The cam sensor is right on top of the intake cam, if it's going bad or has a wiring problem then it could cause this sort of problem.

The cam sensor is a very likely candidate, they frequently glitch out when they get hot, especially when run hard at the track.  They're cheap and it's one bolt to swap them, I recommend bringing spares with you to the track.

 

Keith Tanner
Keith Tanner GRM+ Memberand MegaDork
7/17/20 5:32 p.m.

Chatting with a coworker - that ECU does have on-board datalogging. Also, if it loses power momentarily you'd get a drop in the boost gauge (more noticeably in the tach) and a slight knock. I'd be suspicious of the cam angle sensor and the main relay. But learning how to datalog will help a LOT.

boxedfox (Forum Supporter)
boxedfox (Forum Supporter) Reader
7/18/20 3:32 p.m.
Keith Tanner said:

Email keith@flyinmiata.com with the name on the receipts, I'll take a look at the spec.

That's customer service right there.

Ebmessier
Ebmessier New Reader
8/9/20 8:26 p.m.

In reply to Keith Tanner :

Keith -- I sent you an email earlier today with a datalog of the incident.  It has been happening more and more frequently, now whenever I step down on the accelerator.  Replaced the cam sensor before this track weekend so that's not it.  Car runs fine as long as I keep the turbo boost down.  If I step down, I get a hard bucking. Appreciate any help since I'm at a loss - also replaced spark plugs with no improvement.

David S. Wallens
David S. Wallens Editorial Director
8/9/20 9:09 p.m.

In reply to boxedfox (Forum Supporter) :

Yes, thanks Keith. 

Keith Tanner
Keith Tanner GRM+ Memberand MegaDork
8/13/20 8:38 p.m.

In case anyone is on the edge of their seat - Ebmessier sent us a data log and he was hitting boost cut. A little testing indicates the base boost is fine, so the theory is that someone tuned the electronic boost control a little too close to the boost limit. Easy enough fix, but it's going to require some learning on how to program the EBC :)

Kreb (Forum Supporter)
Kreb (Forum Supporter) UberDork
8/14/20 8:00 a.m.

You da man, Keith. 

Keith Tanner
Keith Tanner GRM+ Memberand MegaDork
8/14/20 9:26 a.m.

I didn't find it, I just put it in front of a coworker :)

AngryCorvair (Forum Supporter)
AngryCorvair (Forum Supporter) GRM+ Memberand MegaDork
8/14/20 10:11 a.m.

last session on day 2, i'd be checking my fuel gauge.

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