Part throttle stumble, 2500-3000 RPM
 

Hey All -
Recently got done installing an AVO T28 setup on my 97'. While I was at it, I replaced the T-belt/water pump. Right now I'm running off of WG only, 5 psi. I'm waiting on my injectors to get here. Fuel/timing is controlled by AEM's FIC, no FMU.

I'm getting a stumble at part throttle, usually between 2500 and 3000. The wideband shows it as a lean stumble.

Here's what I've done/checked so far:
Replaced the wires with a set of 8.5 mm Magstars (same time as turbo)
One set of BKR5E's....then a set of BKR6E's gapped @ .035
New Fuel filter
Tried eliminating the MAF with the FIC, same behavior
Checked the O2 signal with a scanner, it switches....AFR's are 14.3-15.5 on my wideband.
Checked base timing (6 degrees @ 850 RPM)
LT Fuel trims -4% at idle.
Fixed an air leak at the lower injector seals.
Checked all pipe fittings for leaks....I'm showing ~1.3V through the MAF at idle
Fuel Pressure is 38 PSI, rising to ~41ish @ 100 kpa
Connected the bypass connector to run off the stock ECU, same behavior
180 compression across all four cylinders

Now when I went down to Deal's Gap last week, I swapped in a set of 720's I borrowed from a Suby. Performance was pretty reasonable with the occasional hiccup due to 2.5X larger injectors. When I came back, I swapped back to the OEM tan tops. That's when I noticed the issue. I have a set of 440's coming in this week, hopefully that clears it up. My main concern is whether I'm chasing a ghost here. Does the stock ECU act funky with no piggybacks @ 5 LBS? Even when I'm not in boost? The car ran solid before the turbo, she put 107 to the wheels, bone stock, on our Dynojet (120K miles on the motor). If this behavior isn't normal, any other suggestions?

Thanks,

Ryan

The stock ecu acts funky with injectors that are 20-30% larger then stock.

550s for 5psi?

you stock injectors with the controller would most likely suffice....it's quite possible you're just drowning the damn thing with fuel and the stock ecu is trying to compensate.

the AEM can control any size injector directly.

Ryan

No one else is running the FIC. You're kinda on your own with it, so far.

You said the problem began when you reinstalled your injectors. Perhaps there is a vac or fuel leak in there. Or they're just old and dirty. A misfire will show up as lean, even though you're rich in the sense that raw fuel is passed through.

Your fuel pressure is too low. 100kpa should be 48-50 psi fuel pressure, measured before the FPR.

Ryan i think you are experiencing lean tipin riche up the map in that area a hair and all should be better.

It *could* be lean tip-in, my main concern was that I'm seeing this at part throttle in the same RPM neighborhood. I wasn't sure if this was a Mazda ECU issue that rears it's head the minute FI is introduced. Remember, I'm not flooring it, just tooling around part throttle.

As far as fuel pressure goes, Alldata specs between 39-45 psi at atmosphere for a 97'. I don't think it's FP related.

I could buy the old injector issue as the OEM ones were removed when I swapped the 720's in and they sat around for a weekend. Maybe I disturbed something, maybe they dried out and crapped out..(a longshot, sure). I know there isn't a vac leak at the base of the injectors as I did a boost leak check (and used a cigarette to blow smoke into the plenum). I do have a little leakage around the EGR diaphragm but it doesn't seem substantial.

I can't really screw with fueling as we're dealing with a closed loop issue. I add fuel, it takes it away. I guess we'll have to see if my new Subie 440's clear it out.

Thanks so far!


Ryan

+
So is it happening in vac and boost? Or just boost. If it's boost only, it's lean tip in. :gay:
:nono:

could this be a o2 issues, do to lack of o2 clamp. 2500 to 3000 would be the area of 0-1psi on most turbos.

I am wondering if you ecu is leaning out the mixture thinking its running rich and you getting a lean tip in.... if so an o2 would solve it without having to just dump fuel....

Ben correct???

ive heard of some people having better luck with 10k resistors. thats what I put on mine. Havent driven the car yet so I cant say its better or worse than anything else.

Just to clarify, I verified the issue again the other night. It's happening at transition, IE: 100 KPA. My Subie 440's came in last night, I'm going to pop them in tonight to see how she does.

On the plus side, I've been running MAFless now for two day on the FIC. So far so good. I did a little digging around the shop and ohmed out a few IAT sensors. The best match I was able to come up with is a HKS VPC temperature sender. It's within about 5 degrees of the IAT built into the MAF. I put it in the pipe right before the throttle body. It's screwed into a block off plate I fabbed up for an additional injector (AVO pipe). The ECU is happy (no IAT code set or pending) and the temperatures look good post intercooler. FWIW, the VPC temp senders are still available new from various online shops.

Ryan

like whoa. That's awesome. Do you have a part # for the IAT? Could you send me your tune? KA24DET@gmail.com Thanks :)

I don't have a part number for the IAT but if you searched places like MVP, Horsepowerfreaks or Ebay (for example) you'll find it. It's a HKS VPC temp sender. I don't have the laptop with me, I'll post the tune later on.

Ryan

kickass seabass

Problem solved, it was injector related :bigtu: I installed my WRX 440's and she's running solid. I need to tweek the MAF voltage map a tad more off idle to get it 100% like stock. When I get that straight, I'll post my FIC mapping up. You'll have to pull/add some fuel to suit your own injectors though.

A note for anyone looking at the WRX injectors, they are a bit shorter than the OEMs. What I ended up doing was removing the 3 plastic rail spacers and lower seals (Mazda calls them heat isolators). On the bottom I used two new O-rings which, stacked, come up just shy of the end of the nozzle. At the top, I used new O-rings, OEM isolators and another set of isolators stacked. The other set of isolators look just like the OEM ones, I'm guessing they're from the Subie (came with injectors). For bolts, I just used some 12mm ones I found in the shop. No shank, maybe an inch long. The rail tightens up pretty good with no leaks. I also did a boost leak check (with smoke) and I'm not seeing anything from around the lower injector seals.

Performance is damn good for only 5 psi. Hopefully I'll have a chance to strap her down on the dyno tomorrow. I'm shooting for 10-12 psi or whatever these injectors will support :D

Ryan