SOLVED - Weird Stutter Power Loss Under Boost - Fuel Pump Depth
 

**Edit V2: I ended up replacing the whole fuel system and it didn't fix the issue. Next I replaced the whole ignition system and the car runs perfectly now with no breakup under boost no matter how hard I push it. It was a spark issue. See my most recent post in this thread for more details.


*Edit: Moving your fuel pump down does not seem like a valid fix after reading through a ton of posts. This issue seems fairly common though and I'll keep the post updated as I continue to chase down my fuel gremlin. It is narrowed down to the tank though and goes away with a full tank. My best guesses at this point are: clogged fuel filter, loose fuel tank baffle or improperly placed fuel pump sock. It seems like responses to similar issues in the past on various forums point at the fuel sock almost immediately.

Car has a 1.8 FMII w/ 770 injectors and would have random power loss / cutout and surging under heavy boost. It would also seem to go away magically anytime I tried to show anyone the issue. :vash:

I read a ton on here and watched every video I could find. It just didn't make sense. The car still had the factory fuel pump on it, so I figured a good replacement may help the issue. So I replaced the fuel pump with a DW100 and it actually got worse.

This morning I noticed the car only had a 1/4 tank in it and I wanted to do some data logging and send the logs over to Jeremy at FM to see if he could help me. Car was having the issue anytime I went over 4k rpm's yesterday. Nothing changed except me filling up the tank. Problem went away immediately after putting a full tank in the car. WTF?!?!

Happy Boosting!

@codrus another option?

Hm.

My Walbro is a drop-in replacement for the factory pump, and I'm using a brand-new OEM sock, so I don't think this is likely to be the issue on my car. Moving the pickup downwards is a band-aid for using the wrong parts, IMHO.

BTW, the simplest way to relieve pressure on the fuel system (and what the FSM says to do) is to pull the fuel pump relay and then start the car. It'll run a few seconds and stall. Crank it a few times, it will cough a couple times, now the pressure is all gone. Obviously you do this before removing anything else. :)

--Ian

You lost me. What would be the right parts? I had the same issue with the factory fuel pump.

The guy in the video is using a Supra pump and pickup?

--Ian

Oh gotcha. Yeah, I had the same issue with the factory fuel pump and the DW100 (which I read is an excellent replacement for the OEM pump) using a new OEM sock. For me, it was either try and lower the pickup/pump or essentially never drive with less than half a tank. Why Mazda put the pickup in the front baffles me.

Just stumbled on this old thread...
https://www.miataturbo.net/race-prep...sh-foam-62035/

And as usual I jumped the gun a bit. Lowering the pump does not seem like a good solution. There has to be another issue causing the fuel starvation. Good thing is the issue is 100% confirmed to be coming from the tank. As soon as I fill the tank up, the problem goes away. I'm using the oem sock as well. All that is left is to pull the damn thing back out and hope that it is something obvious.

I'm running into the same issue, only not as severe. I'm not using the OEM sock so I'm not surprised. Does anyone have a pic of a known good pump orientation and sock so I can be sure I correct it when I pull it back apart?

Following thread, I will be replacing my pump soon with a DW200/OEM sock.

I pulled the tank apart again yesterday. Yay! I'm using an edelbrock reusable filter and inspected/cleaned it. It looked brand new, so no issue there. On my 1999 NB the return line spits out 1" next to the pickup, so nothing to do there. I had seen that mentioned in some places as being a potential issue. The baffles looked great and looked around in the tank. Everything looked good. When I pulled out the pump, it was almost impossible to tell if the sock was bent over, which is what I suspected.

Stole this pic via google from miata.net
https://cimg5.ibsrv.net/gimg/www.mia...80385e9053.png

This shows the proper orientation of the sock. There is a small area in the tank it will slide into and fit perfectly when it is the correct orientation. See pic below. You need to be careful when sliding it back in, but it should fit right in there when installed properly. It's raining today here, so no test drive, but fingers crossed this was my issue. I'll update when I can test drive.

https://cimg5.ibsrv.net/gimg/www.mia...b5390d7ef8.jpg

Did you get the proper factory sock that is on a 45 deg angle? If you have a right angle sock like that one shown will stick up out if the fuel and starve. The pump actually sits on a 45 in the tank so that's why you need the angled sock to make it level in the bottom.

Yup! The DW sock supplied with the pump was flat would have definitely caused issues. That damn oe sock is pricey though!

After all this, I ended up replacing the whole ignition system because the fuel system had already been fully replaced and it didn't fix the issue. Fixed the car 100% and it runs like a bat out of hell now.

Thanks to Jeremy at FM for reading the data logs and giving me good input. It was obvious there was a spark issue once I finally got a good data log.

I'm positive now what I thought was a fueling issue was actually a spark issue.

Solution: new battery, new plugs, new wires, new coils and a new alternator.

Replacing the above parts fixed the problem and the car now runs the best it ever has.

My suggestion to those who have been having similar issues under boost, bite the bullet and spend the $500 to replace the whole ignition system. It was worth every penny for me.

I considered going COP, but I'm glad I just replaced the oem coils ($225 from Oreilly with lifetime warranty) because they work great. I'm doing 12psi with them and zero spark issues.

Updating first post too.

@LukeG, $225 local for both coils?

I've been wanting to replace my originals. What brand does oreilly's sell?

Here is a link... Import Direct Ignition 23-0405 - Ignition Coil | O'Reilly Auto Parts

Import Direct Ignition - Ignition Coil

Line: IDI Part # 23-0405$225.99 Each

Was a little hesitant to go with a random auto parts brand, but they work great and have a lifetime warranty. Definitely enough spark for a car on boost (I'm at 12psi).

was yours doing this? Listen around 3500-3800rpm

https://youtu.be/xtt6Y-oWnSk

I remember the issue being a little bit faster cycling in the way it would drop and then regain power, but basically that seems like what mine was doing. Keep in mind there are literally a dozen things that could cause similar symptoms. What I posted above is just what simply worked for me.

Yeah i know. Ive been chasing it for a month now. Even sent my 300 mile old injectors back to ID for cleaning and flow testing. Tried 3 different coil packs, new plugs, plug wires, cam sensor, checked timing, compression. And tons of researching/head scratching. I will try a new alternator tomorrow

This was recorded 5 mins after the misfire video.
Idles fine. But then sometimes it idles like shit. I just dont get it

I've been down the same rabbit hole and ended up replacing my injectors too. if you have replaced the whole ignition system and it is still doing it, I would recommend getting an aftermarket fuel pump and checking ALL of your grounds. I had some shitty grounds that I'm sure were causing some issues as well. I'd also start eyeing the solenoid pressure valve, cam angle sensor and idle air control valve. They in order of cheapest to most expensive.

There are some threads on the msm cars having serious "Bog" issues caused by the factory solenoid pressure valve. I have never seen it mentioned on this forum, but it is a known issue. The replacement part i got on ebay was only $30 and takes about one minute to swap. Pull yours off and look up the part number on ebay. This was mine:

http://www.ebay.com/itm/K5T46591-For...-/322065287338