X64v Posted March 14, 2007 Share Posted March 14, 2007 This has been plaguing me since I made the switch from my su's on Thanksgiving. The engine will run alright to 4000rpm, at which point it promptly falls flat on it's face. Even with it floored while out of gear, it won't reach much past 4-5k. My NBO2 sensor (along with everything else I know about tuning) shows that it's just dropping dead lean. Figuring that out was the easy part. The part that's stumped me for the past three months is why is it dropping lean? Every single mechanical component in the fuel system has been tested or replaced. Lets start from the top: Clean tank, gas flowing out the drain plug hole through 3/8" line into a clear fram filter, into a new MSD pump (stock nissan pump was used as well, with no filter before), then through a new fram metal filter, through the stock hardline (have also totally bypassed the hardline with new 3/8" rubber fuel line), into rebuilt 338cc ford injectors (also used oem l28 n/a injectors), through a stock FPR (holds ~36psi at ambient pressure), then back to the tank via the emissions hardline and one of the 1/2" vent tubes. The tank is vented just fine, and as I just showed, every single part of the fuel system has been tested/bypassed/replaced. Below is a datalog of a 1st-2nd gear run of the problem. I floored it in 1st until the problem popped up, then shifted to 2nd and ran wot again until it maxxed out. On the graph, you can see it best climbing through 2nd gear where TP is at 100% with the rpm's climbing, and then O2 just shoots lean. My ve table is layed over the O2 graph, showing that my fuel map is rising through 90-95% ve just fine. I have tried using fuel maps up to 150-160% ve (way too high for an N/A l24) with the same result. If you have any idea as to why this is happening, or have any questions about my set up/what i've tested, please speak up. Quote Link to comment Share on other sites More sharing options...
Gavin Posted March 14, 2007 Share Posted March 14, 2007 Could you post the same datalog with the pulse-width graphed? The obvious question, and dont be insulted—it must be asked: is the fuel pump your currently using for EFI or your old carb setup? Do you have a fuel pressure gauge? You should rev it up and make sure its holding pressure. I'll keep brainstorming... - Oh hey, maybe its a spark problem resulting in an unburnt mixture that appears as lean to the O2 sensor? Just throwing out ideas. Quote Link to comment Share on other sites More sharing options...
veritech-z Posted March 15, 2007 Share Posted March 15, 2007 Well, if you look at his post, it says he tried it with a stock L28 pump, so I suspect that it's not a lack of fuel pressure. Also, a pump that's putting out 36psi is going to be spitting fuel out of the SU vent tubes (ask me how I know that ). I really hope somebody knows the answer to this, because my car won't get over 4k rpms either. I've got MSI ver. 2.2 (fuel only). Mine is almost acting like it's got a rev limit function or something, but I haven't found any settings to that effect anywhere in Megatune... Quote Link to comment Share on other sites More sharing options...
z-ya Posted March 15, 2007 Share Posted March 15, 2007 I would suggest routing a temporary fuel pressure gauge so you can see it while driving with the hood popped open. This way you can verify that the fuel pressure is adequate when it leans out. Quote Link to comment Share on other sites More sharing options...
TONY C Posted March 15, 2007 Share Posted March 15, 2007 I am having the same issues . running msII. walbro 255lph sard regulator 6an lines all the way. only diff mine is after 30-45 minutes of driving. hooked up a gauge and bingo. no fp around 4k. SARD fpr's must be junk.?????? anyone.. hook up a gauge. not to steal a thread. but anyone have regulator suggestions. Quote Link to comment Share on other sites More sharing options...
z-ya Posted March 15, 2007 Share Posted March 15, 2007 I've had good luck with the Aeromotive regulators: http://store.summitracing.com/partdetail.asp?autofilter=1&part=AEI%2D13109&N=700+308633+115&autoview=sku Quote Link to comment Share on other sites More sharing options...
TONY C Posted March 15, 2007 Share Posted March 15, 2007 that's what I thought. should the boost ref be hooked up with msII though? Quote Link to comment Share on other sites More sharing options...
X64v Posted March 15, 2007 Author Share Posted March 15, 2007 Don't worry about asking seemingly stupid questions, we all make dumb mistakes. Yes, the msd pump is an FI pump. Veritech - That's EXACTLY what it feels like. Climb up just over 4k and BAM feels and sounds like a rev limiter. Except mine's cutting 0 out of 5 sparks at 25,000rpm... On the question of ignition, I'm running fuel only through megasquirt, and this exact same ignition set up ran just fine with my su's. Ah, forgot to mention the temporary fuel pressure gauge thing...when it's cutting lean, the pressure needle bounces back and forth between 0 and 35 as fast as it can (I assume it's dropping to 0 when the injectors open, telling me I have a lack of flow for some reason...). Problem is, I have no clue why I'm getting this lack of flow (that was the reason I bypassed the tank pickup and feed line and used different pumps and all that). And here is the same datalog with the pulswidth...which (as I see it) totally eliminates the electronics from being the problem. Quote Link to comment Share on other sites More sharing options...
mario_82_ZXT Posted March 15, 2007 Share Posted March 15, 2007 Maybe the pump is cutting out or the power to it is? Or your fuel system could have chunks flying through it (rust chunks from the gas tank). Mario Quote Link to comment Share on other sites More sharing options...
X64v Posted March 15, 2007 Author Share Posted March 15, 2007 Same power source as I ran with my electric carb pump, and I ran for ten or fifteen minutes at a time over 4k. And I thought about that, too, but I banged up the bottom of the tank with a rubber mallet and then drained it, and it came out clean, and then I bypassed the tank feed line by feeding from the drain hole, and the gas that comes out is clean, with no crap in the clear prefilter. But please, keep the ideas coming. Quote Link to comment Share on other sites More sharing options...
linluv84 Posted March 15, 2007 Share Posted March 15, 2007 Stock ZX regulators are pretty easy to find and pretty reliable too. Watch the tach in MT, I used to get some nasty spikes in the tach signal until i added a resistor to filter out the noise... Quote Link to comment Share on other sites More sharing options...
X64v Posted March 15, 2007 Author Share Posted March 15, 2007 Yup, I was actually getting a nasty spike while running spark control, so I took that away and just had it trigger off the coil -, no apparant spikes on the tach or on the rpm graph anymore. Quote Link to comment Share on other sites More sharing options...
HB280ZT Posted March 15, 2007 Share Posted March 15, 2007 I had a friend of mine that had a problem like this and it was the line from the tank to the fuel pump. Basically it was twisted and compressing at high rpms when at the track, which was reducing fuel flow at high rpm's. Also another trick you can try is to hook a light up to the fuel pump and see if the light is changing when you are at rpm? I am running my pump directly off of the battery by using a relay from MS just to make sure I am getting good power to the pump at all times. Also have a clear filter betwwen tank and pump to make sure I am getting fuel and no stuff in the pump. Just a thought or two! HB280ZT Quote Link to comment Share on other sites More sharing options...
z-ya Posted March 15, 2007 Share Posted March 15, 2007 Just to be sure, this is how the fuel circuit should be connected: tank outlet -> filter -> pump -> filter -> fuel rail -> regulator -> return back to tank Without the engine running, disconnected the fuel line where it enters the fuel rail, and stick it in a fuel jug. Wire up the pump so that it run continuously. Check to see that you have a lot of flow (zero pressure in rail). Then do the same test on the return line. You should get a lot of flow out the return with the engine not running (fuel rail pressurized). Quote Link to comment Share on other sites More sharing options...
woldson Posted March 15, 2007 Share Posted March 15, 2007 tank outlet -> filter -> pump -> filter -> fuel rail -> regulator -> return back to tank is it possible to tank outlet -> filter -> pump -> filter -> regulator->return to tank->fuel rail Quote Link to comment Share on other sites More sharing options...
Matt Cramer Posted March 15, 2007 Share Posted March 15, 2007 Could you post the whole datalog file, not just a screen shot? Quote Link to comment Share on other sites More sharing options...
BayAreaZT Posted March 15, 2007 Share Posted March 15, 2007 Could it possibly be EMI interference screwing with MS. What kind of spark plug wires are you using? Just throwing out ideas. Quote Link to comment Share on other sites More sharing options...
X64v Posted March 15, 2007 Author Share Posted March 15, 2007 Just to be sure, this is how the fuel circuit should be connected: tank outlet -> filter -> pump -> filter -> fuel rail -> regulator -> return back to tank Without the engine running, disconnected the fuel line where it enters the fuel rail, and stick it in a fuel jug. Wire up the pump so that it run continuously. Check to see that you have a lot of flow (zero pressure in rail). Then do the same test on the return line. You should get a lot of flow out the return with the engine not running (fuel rail pressurized). Yup, that's how it's run. And I will do the visual flow test next time I get a chance. I'm running NGK plug wires. Matt - Here's the whole datalog file. I did the 1st-2nd run, then pulled over and waited for some cars to go by, then turned around and did it again, towards the end of the file. datalog.zip Quote Link to comment Share on other sites More sharing options...
Matt Cramer Posted March 15, 2007 Share Posted March 15, 2007 Thanks for posting the data log. I see that everything seems to be operating normally from the electronics' perspective, but it's like the fuel suddenly gets cut off. I think it may be that fuel flow drops off with pressure. A system that can deliver the right volume of fuel at typical carb pressures may not be up to that at injection pressure. Quote Link to comment Share on other sites More sharing options...
cygnusx1 Posted March 15, 2007 Share Posted March 15, 2007 The BIG CLUE for this mystery is the fuel gauge needle jumping from 36psi to 0psi as fast as it can during the anomoly. It should be staring you in the face saying: 1) The fuel pressure pulsing is PROBABLY caused by the injectors opening-closing. 2) The 0-psi is when they are open and there is not enough fuel to refill the rail fast enough. 3) Lean spike TOTALLY corroborates this. My guess is that your fuel delivery setup is flawed. -Plumbing restrictions somewhere. -Too much fuel returning to the tank...ie. not enough "back pressure" from the regulator at that RPM/LOAD range. -Injectors sticking...maybe but I doubt it because it is leaning out. OBSERVATION: The pulswidth is doing what it should be doing. The O2 levels go lean really suddenly. Strangely enough, it doesn't taper off as if you were reaching flow limits of the fuel lines. It's almost like someone shut-off a petcock in the fuel line or opened the return line wide open. I would check four things in particular: 1) Pressure regulator 2) Pump cavitation 3) Broken fuel filter element. 4) Collapsing fuel suction line before the pump. Quote Link to comment Share on other sites More sharing options...
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