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Hey guys, I finally got my 951 back on the road again.... And Im not 100% whats going on with it.
So I was starting to thing my clutch was slipping, but now Im not sure.
When I get to 4K+ rpm it back fires and goes lean (I think, and by that I mean im not sure it it went lean on its own or because i was letting off the gas with all the commotion)
SO i haven't really gotten much chance to really drive the car, just run up and down neighborhood streets to test it out and on and off the near by freeway between exits. It has an EFR turbo, and a 3.5" exhaust, the turbo spools really fast and boost start building a lot earlier than stock k26.
At first I was thinking "wow the boost builds really fast and as it does it blows through the rpm" but after 4k things go crazy! I hear crackling and back firing and once saw flames out of the corner of my eye. I was thinking oh the boost controller is opening up (greddy Profec B spec II) I tried playing with ti and raising the boost but it didnt seem to make much difference. I tired it a couple different ways, I know just going WOT does it for sure, so I just eased into it, and same thing, and even just Regular driving but not up shifting,so low boost, not even near the limit like 5-6psi, once it gets over 4k same thing.
and it was hard to tell what was going on, as its a bit of an "earthquake" moment. But I started to think maybe its "blowing through the Rpm" because its slipping when the power comes up, except that even easing into it I get the same result AND I can't even get it go near 5k.
Just to note I have no idea about the clutch in this car (other than that Master has been changed and its been bled.) I think it its a little low according to the way to measure where the end of the arm its in the inspection hole, which also lead me further in the direction of the clutch.
and for tuning it has a Danno/Guru chips, and Autothority MAF, I know not the latest and greatest, but don't think that should cause these symptoms.
Recall that even though the PSI on the gauge is the same, different turbos (especially newer ones) can flow way more actual air mass.
You have one of the latest and greatest turbos on an engine that is otherwise setup for the tractor-spec K26.
I suspect your higher-RPM tune fueling is not right for the capacity of that new EFR turbo. At this point you owe it to yourself to go to a newer standalone type ECU that runs on MAP.
Recall that even though the PSI on the gauge is the same, different turbos (especially newer ones) can flow way more actual air mass.
You have one of the latest and greatest turbos on an engine that is otherwise setup for the tractor-spec K26.
I suspect your higher-RPM tune fueling is not right for the capacity of that new EFR turbo. At this point you owe it to yourself to go to a newer standalone type ECU that runs on MAP.
While I would like to upgrade the ECU, I just need it drivable. don't care about power at the moment. But I am not so sure that is the issue, because even at low boost it does it. Would a car backfire if it wasnt getting enough fuel? On my 931 when the tuning was off it would just bog down and cut out. FWIW the chip in it now was for a K29! It almost seems like the Boost limit was going off. (but I don't know what that is actually supposed to feel like) and Im not even sure this car has that any more?? Was considering putting in the stock chip just to see what difference it would make.
im wondering what else it could be? TPS? timing sensor?
any other thoughts here? Like how can i be sure if its the clutch slipping or not?
If it is truly backfiring and going lean, then it's not the clutch. Clutch slip won't affect the engine other than letting it rev fast. If it feels like it's hitting a brick wall, then it's likely a fuel cut from overboost or some other issue. If it just feels like garbage like it's stumbling and missing, then I'd look pretty hard at tuning first especially if you haven't done that yet. There are so many things it could be, you'll just have to start eliminating them one at a time. i.e., check fuel pressure, check spark plugs, check injectors.
If it is truly backfiring and going lean, then it's not the clutch. Clutch slip won't affect the engine other than letting it rev fast. If it feels like it's hitting a brick wall, then it's likely a fuel cut from overboost or some other issue. If it just feels like garbage like it's stumbling and missing, then I'd look pretty hard at tuning first especially if you haven't done that yet. There are so many things it could be, you'll just have to start eliminating them one at a time. i.e., check fuel pressure, check spark plugs, check injectors.
Yeah, thats kind of what I was thinking, Just trying to narrow it down. Its just so abrupt. Could It be spark plug gap?? It doesn't seem boost related, seems more RPM related than anything.
Could the Recirc valve be stuck? I doubt its running out of fuel, im not pushing it at all
Could the MAF have anything to do with it? since its an old school type? is has the separate potentiometer attached.
would the overboost cause backfiring? and what would cause a false overboost?
Everything you mentioned is a possibility. You just need to do some legwork to start narrowing it down. Check the fuel pressure, read the plugs, start with the easy stuff. Collect some data from an 02 sensor. There are so many things that can cause this, it's impossible to diagnose without more data.
It looks a little hot. I would change those plugs out for Bosch WR7DC or NGK BPR7S. Maybe one set cooler.
A misfire will show as lean condition, since the oxygen was not consumed by combustion.
I had exact same symptoms on my stock 951. All new vacuum lines.
It turned out the vacuum line going to the fuel pressure regulator was clogged with a rogue piece of rubber from one of the tees.
Could be lucky and FPR just isn't receiving the vacuum/boost signal? But yeah, get some fuel pressure numbers!
Ok I just got a pressure gauges, will put it in and see.
wonder if the Injectors could some how be an issue? I doubt im running out of fuel (at least with what should be able to be supplied) The thing im looking to clarify, is IF its RPM related, rather than boost/air related, what would show with one, but not the other??
If the WG is opening (tial) that wouldnt cause this would it?
I dont know why, but I some how feel like spark is getting cut, I could be totally wrong though.
Just got the car back in the garage. while Parked I brought the revs up just over 4k, and didnt get any cut out or stumble...so theres that, Im going to install the FP gauge now, but with out being able to see it when the car is driving, will it help at all?
one thing I noticed is that the AFC-r isnt showing the throttle position (which is did in the past...years ago) not sure if that is indicative of anything.
If you have found a problem with the throttle position signal, fix that first. It might not be what's causing your problems, but it might be, and either way you've fixed something.
03-24-2024, 05:21 AM
Whats going On???
