My 1997 NA1.8 runs lean at normal (40s psi) fuel pressure high speed WOT.  Cranking pressure up to 60 psi is still 14.5:1.  64 psi 13:1.  65 psi 11.5:1.  66 psi 10.5:1.  Not only do I need very high pressure to hit 13s:1, but 1 psi higher or lower has big impact.

 

On the dyno fuel pressure dropped ~5 psi from idle to full speed/load.  Does this indicate restriction before regulator?

 

I have replaced fuel pump, fuel filter, fuel pressure regulator (now Advanced Autosports), air:fuel meter (now AEM), fuel pressure gage (AA), engine controller, and ran injector cleaner.  No improvements.

 

Appreciate suggestions - long time lurker, first time poster

Welcome to the club.  The lean '96-'97 club that is.

I have a '96 and have spent many hours and a lot of $ trying to correct the same issue.  First, I think it's normal that these year cars need more than factory fuel pressure to get to the AFR sweet spot.  I have literally changed every part under my hood that might impact this and still don't have it completely solved.   Here's a little more info.

A healthy factory fuel pump will only maintain on a straightaway at most low 60's PSI at WOT no matter where you set it at idle.  You might want to find a shop that can perform a smoke test and check for any vacuum leaks or exhaust leaks.  I wouldn't mess with trying to build a smoke tester yourself. Find someone that has a real one and knows how to use it.   We found a couple small leaks and corrected them.  I also found small leaks at the base of the injectors as the rubber grommets that they seat into were old and hardened.  Still, these cars seem to be more sensitive to intake air temp and possibly fuel temperature.  On a cooler day I can now get decent AFR at 60PSI.  On warmer days it's still too lean. Keeping water temp down with a big radiator may help a teeny bit. Change your engine coolant temp sensor if you haven't, but it's a bitch back of cylinder head. I've had 3-4 air flow meters on the car including a new one, no difference.  3 sets of injectors including 1 brand new set (expensive) with all 3 sets flow tested.  No difference other than we did find 1 or 2 used injectors that were a bit out of range.   The new injectors were spot on.  You should probably get a set tested as you might find something there.  

Where I left off last fall on this was observing fuel trims with an OBDII scanner on the dash.  I was seeing negative long term fuel trims in the 10% range which means the ECU is pulling some fuel.  The ECU doesn't know we are running high fuel pressure yet it's still trying to lean it out a bit.  It may be that these early OBDII cars in open loop were simply programmed this way.  

I haven't given up yet.  The ECU does have some drive cycle "learning" that happens so it's possible that powering the ECU on and off (or not) and full throttle track driving doesn't satisfy that cycling.  More time will be spent on this in '24.  Happy to share findings with you or anyone else that is scratching their head on this.   

The functionality of a real forum site like this is far superior to FB IMO.  Organization of topics, search and overall navigation is better.

Sorry, got doing other things and this fell off the current list.

 

 

Pads - Hawk Blue, Hawk ER-1, Pagid yellow's.  All act the same in regard to brake drag.  We've reduced them all down to the backing plates.

 

Pressure build via fluid - I don't think so.  While everything is hot and the pads are binding you can open the bleeder and nothing changes.  If there was pressure on the fluid, opening the bleeder would remove it.  You're not the only one who has suggested this as an issue.

 

From what I can tell it is the piston binding in the caliper.  I was expecting that the Mazda seals would do a better job than the Dorman/parts-store grade, but they weren't appreciably better.

 

Another question for the collective group - with the bleeder open, and everything cold is there a measure of how stiff the piston is to push back?  Can you do it by squeezing it with just your hands? 

 

Drago calipers are looking like a decent option if they have good track record of behaving. 

A video showing brake drag on jackstands hot would be meaningful but tough to do in NH this time of year.  Hot or cold with bleeder closed you should be able to push back the piston into the caliper using channel locks pretty easily with 1 hand.   I've had a caliper or two drag over the years and just replaced them usually with East Street rebuilds and that has done the job.  A pad bind (cockeyed) or pin bind can do that but it sounds like you've checked that.  

Larry I had a similar experience at Road America a couple years ago.  The pedal went to the floor entering a corner and then was good the rest of the session.  We bled them after and all was fine next session.  Sunday afternoon while driving to the grid the pedal again went to floor.  I then found a slight leak at the master cylinder.  Replaced that and life has been good brake-wise since.  Strange for sure but as others have said, many of our cars are running an old brake master, proportioning valve, brake booster vacuum hose (which is valved), brake booster and lines.  If you have a 30 year old master, I'd replace that even if you find another problem.