I'll try to keep it short and to the point.

At SOW the car ran great for the first session. Half way through the second, it developed a little stumble that would show up sometimes when I started applying throttle. Then I noticed it was running a few tenths leaner in boost than it should be. The stumble began to get worse and it began to get even leaner in boost so I ended my day early. Tried to drive it home and I could see that every stumble was associated with the AFR going full lean. It got progressively worse (more frequent) to the point where in a given span of time it would be stumbling/not producing power and be full lean more often than not, so I parked it and towed it home.

My first inclination was fuel pump, since I was still on the stock one. Just replaced it with a Walbro 255 and it has not helped. When I start the car it cranks and fires up, the AFR gauge reads full lean, and the car dies. If I give it some throttle, the rpms will rise and the car will continue to run, but AFR stays full lean and it runs really rough (I presume because it is running on little to no fuel).

So, datalog is below. In it I started the car and let it die. Then I started it again and gave it some throttle to keep it running for a moment, and when I let off the throttle it died.

- Fuel injectors are rx-7 units that I had rebuilt/cleaned before installing <2 years ago so I think those should not be the culprit.

- Fuel filter was replaced 1 year ago, but might not hurt to pick up another cheap one and try that...

- Fuel Pressure Regulator? Mine is still the original 20 year old one... But my understanding of the FPR is that if it were to die the car would be running too rich not too lean?

- I tried using Megasquirt to add more fuel while the car was running, but the AFRs did not budge.

- Is dead o2 sensor a possibility? If it were to die, does the ECU depend on that sensor in some way that without it it wouldn't be able to run the car right?

- Any suggestions/input greatly appreciated.

 

There is probably not enough authority in the EGO correction to make the car die. By "probably" I mean incredibly doubtful that someone screwed up that bad.

Run the TS screen with all sensors and see which one is whacking out.

 

No TS - still using Megatune. Anyways, all the gauges look fine, except for the obvious one - the AFR being way lean (18:1)


By this you mean that a failed o2 sensor reading wouldn't have enough authority to actually make the car die right?

 

My money is on the FPR. Get a fuel pressure gauge and watch it

However, if it's an ignition misfire, it will make the wideband go full lean. Is the stumble sharp and defined, or a bit more muddled?

 

Back when it was running and stumbling intermittently (because now it's not even running), it was a more "muddled", or softer stumble.

I once had a miss that would happen occasionally that was really harsh - like the whole car was shutting off for a split second - that turned out to be the bolts that held the coil packs to the valve cover coming loose (since they ground through the VC). This was nothing harsh like that, and the rpms don't drop like it did then either.

This is the vid from that second session. If you jump to 20:00 and you have speakers that have decent bass (my laptop speakers don't pick it up) as I pull back into the pits you can hear that although I'm at steady throttle there are occasional burbles/stumbles - you can hear them in the exhaust note. That is how it was at first. When I drove it home, they increased in frequency until there was more of those stumbles than there was time running properly, and finally it was just reading lean all the time and stumbling 99% of the time with an occasional half second burst of running ok and producing power, that's when I parked and towed it.

 

Get TS now, it will help you diagnose any input into the computer with either a number or a bar graph. I recently used it to locate a broken wire in a friend's car.

EGO correction typically does not have 100% authority, it won't change the VE figures more than 5 -10 points depending up on how it's set up.

 

OK, so o2 sensor is out of the question.

I'm going to have my buddy bring his NA over and I'll try swapping his FPR over since I know his is new and good, I'll also try to swap over whatever else I can think of, one at a time, to see if anything helps. And I'll replace the fuel filter.

-Ryan

 

Try unplugging your IAC and see what the car does. I had a coil pack go out in a friend's car one and we assume raw fuel was on the WBO2 which shows full lean if unburned. See what the plugs look like and go from there.

You need the TS sensor log window to see if any wires are fucked on the car, since you're is over 20 now things like this happen.

 

Plugs look lean. I pulled them trackside to try to get an idea of whether I could trust what the AFRs were telling me. All white tips, and cylinder 1 was white around the rim too with minor pitting. I'll pull them again tomorrow and shoot a pic.

I unplugged the IAC valve and started it - no apparent change - fired up then died after a second of chugging lean.

 

I'm definitely going to second the tunerstudio idea, you can get a lot more information from the car.

 

I know Sean! lol

I'll post updates tomorrow when I try some more stuff

 

Disregard what I said at first, one thing I did notice your O2 reading didn't really change. Would a bad wideband o2 sensor be the cause of this?

 

Another point to consider... Stock FPR with a walbro 255 equals about 15 psi higher than base should be, from what I've read. You might actually have overcompensated your lean condition and gone too rich. Does it smell like gas? I 2nd the get a fuel pressure guage sentiment...

 

I have heard this about the walbro 255, can't you compensate for that with tuning on the megasquirt? However, another question to ask is does the extra fuel pressure wear out the fpr quicker?

 

OK who has a suggestion on where to get a fuel pressure gauge, what kind to get and how does it get installed? Is it an in-line thing? And if so, where is the best line to put it in at? As far downstream as possible - right before the FPR?

-Ryan

 

For a stock set-up you'll need to make an adapter for the factory fuel line with a 1/8NPT bung for the pressure gauge. You can also just buy a Fuelab regulator like I did.

 

OK what the F is going on here now?

First of all, I pulled the plugs track-side after the stumbling began. All 4 plugs had very white tips and plug #1 had slight pitting around the rim - as if from being very lean

Now, I replaced the fuel pump with the 255 - it would start then immediately die. If I gave it throttle, I could keep it running but it would be stumbling badly and show full lean on the AFR gauge.

I just replaced the FPR with a working one from a buddy. Started it up and it died. Gave it some throttle and it would show me decent AFRs for a bit (14-16:1 bouncing around) and had intermittent stumbles that were accompanied by AFRs going to full lean each time. The longer I ran it like this, the worse it gets - the stumbles become more frequent and it shows full lean more and more often basically this is back to how it was when I was trying to drive it home. It seemed like the longer it ran/the more it warmed up the more pronounced the problem became.

So, I pulled the plugs, expecting to see them all white but here is what I've got now:





What in the world is going on? It looks like each cylinder is burning differently. 1 and 3 look way rich, 2 looks lean, and 4 looks to be in the middle but has white on the tip but black on the ring around...

So... uneven burn? Should I look at fuel injectors - I have some tan tops I could swap in and change REQ_FUEL accordingly and see what happens... Or should I look at the ignition system - plugs aren't burning the fuel? Maybe they got damaged while I was running lean - I've got some new BKR7Es coming within the next hour so I'll try that. Or wires? Or coil pack?

-Ryan

 

dude I know Genesplicer had some really weird stumbling issues on track last time. and Collin had the same problem, Check your CAS.

Not sure if it will make it run lean or not, but it caused stumbling and the RPM gauge kept jumping around a lot. They both BROKE the CAS connector plastic. I guess it just got brittle from the heat and the vibrations from the gators did it in.

I tried to watch his AFRs in video, but it was hard to see (8:29, to see the stumbling/lurching):

 

You're running on two cylinders. Going full lean, barely starting, and stumbling like it's running on two cylinders is exactly what it's like when you loose a batch of coils or injectors.

 

Makes sense Curly. The new NGKs are supposed to be here any minute, and I can get a set of working plug wires and ignitors/coil pack from my buddy's car - I'll swap that stuff in and see where that puts me.

A couple weeks ago the bolts for the coil pack to the valve cover came loose and I was having real bad misfires from that since it uses those bolts to the VC for ground. I found the issue and fixed it and it ran smooth afterwards, but maybe that had something to do with shortening the life of one of the ignition related components?

What if some of the black on some of those plugs is oil? My rings have been slowly dying, although the car still makes great power, so if the rings got worse, could excessive oil in the combustion chamber have something to do with this?

Track - CAS is not loose or anything and the plug on it looks OK.

-Ryan