11 replies to this topic

[Keith Novak]

My car has been sucking down enormous ammounts of gas running fully stock fuel air bits and while I'm about to install a adjustable FPR, I think something is off causing this change and don't want to put a bandaid on what could be a sucking chest wound.

 

Last year, completely predictible fuel consumption.  I budgeted 9 gal/hr and was never too far off.Today I sucked down 6 gallons in half an hour and have been seeing similar results where I throw in a gallon or two extra and run it dry.  Side notes:  I planned to change the fuel filter early this year but when I opened the tank, it was new and the tank was squeeky clean.  One hose clamp was missing though which caused a reandom short term fuel leak once or twice then stopped leaking before I found it.  I doubt that's related but happened about the time the fuel consumption shot up.  This weekend I found my CAS is crapping out.  It started changing timing randomly by several degrees this weekend.  I tried one a friend had...ran smoother but had a bad connector so not much learned other than don't race with a bad CAS or you could lose all powere very suddenly.  Put the known iffy CAS back on and it missed intermittenlty and once again sucked up too much fuel. The electrodes on the plugs looked good but lots of black carbon elsewhere.Something I haven't seen before with plugs used 1 weekend.

 

Could the timing issue with the CAS be causing the rich fuel sucking issie or should I be looking elsewhere?

[Michael Novak]

AFM????   PLUGS?????   Start with the basics---AFM on the car or dyno... What do the plugs look like?.   Injector leaks?

[Jeff Wasilko]

Check the water temp sensor feeding the ECU. If the ECU thinks the car is never warming up it'll run really rich.

 

I had that fail and burned thru more than 1/2 tank in 20 minutes at the Glen.

[Keith Novak]

Thanks Jeff.  I never would have thougth of that.  I'm pretty sure it's the original one.  If that turns out to be the issue it's a really cheap fix.

[Brandon]

Another suggestion would be to check/have your injectors cleaned & balanced.

 

I too experienced abnormal fuel consumption and coupled with my desire to run as close to min-weight left me not taking checkered flags at too many events in 2012.  Turns out I had one injector flowing significantly more due to it being dirty and not closing properly (dripping during off-cycle).

 

Sent all four to Marren Fuel Injection in CT, the faulty one never did come around in-line with what the others were flowing so they swapped it out with one of a similar flow to the others, and $125 later I've got four 'balanced' injectors.

 

While I can attest my fuel consumption returned to nominal (relative to others in the field) I still have a tendency to run 'slim' on fuel reserves.  Time to go on the "Drago Diet"!

 

HTH,

Brandon

[Cy Peake]

Smaller, cheaper injector cleaning and flow testing outfit: www.cruzinperformance.com

[FTodaro]

I always use Dave at advance Auto sport his prices are competitive, he knows Miata Injectors and he sends you a nice little data sheet on the flow results of the injectors. Confidence is important to me.

[Brandon]

Call me a traditionalist - my car had a Marren sticker on it when I bought it.  

 

But Cruzin looks like a respectable place to send them off to.

 

Think of it like fuel injector camp I guess...

[Keith Novak]

I only have about 12 hrs on the injectors since I got them back from Miatacage for cleaning so that's probably not my issue but still good input.  Thanks!

[Johnny D]

No expert, total WAG, O2 sensor?

J~

[Keith Novak]

Apparently it was the temp sensor. I finally got to test it out today with a new one and the fuel consumption went right back to normal.
Thanks!!

[Jeff Wasilko]

Apparently it was the temp sensor. I finally got to test it out today with a new one and the fuel consumption went right back to normal.
Thanks!!

 

Score one for me!