I need your help.. My long term fuel trim according to my obdii software is bottoming out around the -25 mark on each bank and causing 1127/1129 codes. I've done these thingss so far but to no avail.. Replaced MAF Replaced FPRs Reinstated my bypass valve Tested system vacuum to 27 hg Replaced upstream o2s Replaced downstream o2s along with spacers Performed idle test with no airbox attached (no airfilters) Verified that gas was at least present in one return line (attached to fpr) Wiggled main return line to tank, didn't feel pinched Ran Techron fuel injector cleaner Verified o2 plugs were plugged in correct plugs The issue persists, with extreme prejudice. Funny thing though it seems to only be like that at idle or very low throttle. With much of any throttle input, the LTFT jumps up to around 0. I'm not talking wide open throttle, just a little, while well under 4000 rpm keeping in closed loop. The one thing I did do which caused the short term fuel trim to jump up immediately was to put a fuel pressure guage on my fuel filter and depress the pressure relief letting fuel flow into a bucket while car was idling. RPMs dropped and STFT rose immediately. I think though that my fuel pressue is ok since I have new FPRs and as soon as I cut ignition, fuel pressure on the fuel filter drops to the 3.8 bar mark (and stays within 3 bar for an hour), so something is regulating the pressure to that range, must be the FPRs. What am I missing? The car runs great .. on occaision it does idle rough if left to sit 30-40 minutes. I'm still getting used to my operational bypass, ***** cat.
A leak in the vacuum circuit which prevents the FPRs to reduce the fuel pressure at idle ??? Check all the hoses, from TBs to FPRs, in-between TBs, from TBs to NR valve, ... up to the tank. Measure vacuum pressure at FPRs level, at idle and check it decreases (pressure increase) when you blip the throttle. As it affects both banks, be sure that the fuell return line is not clogged or that there is no blokage. Finally, measure the fuel pressure in the rail.
There was a poster with a Long term fuel trim problem which turned out to be a throttle linkage adjustment that was mis-aligned. You want to check that too.
I put a vacuum gauge on one of the FPRs vacuum supply line today and read 20cm at first idle, then eased down to 12 cm once it warmed up a little. I blipped the throttle and saw the vacuum dropped. I'm reading in the service manual and they say apply between 20 and 60 cm of vacuum when you're testing fuel pressure. Do I have enough at a max of 12 cm at idle to operate these FPRs? I then stuck the vacuum on the FPR and started the car while watching the OBD, then applied 60cm but couldn't really see or hear much change.
Jeff, you mentioned elsewhere that you'd measured fuel pressure. Was it as high as 7 bar? I don't profess to understand how the FPRs work on the 355 but with pressure as high as that (and which sounds very high) plus your low vacuum sounds to me like you might be getting close. Maybe post where you measured pressure and what the readings were and someone can confirm whether or not that pressure is high?
I put a fuel gauge on the schrader valve on top of the fuel filter. Actually, I think this is just there as a fuel relief port not as a pressure test port, but as Eric has stated, checking fuel pressure at the fuel rail is not an easy task, and I actually have no idea how to do it. The wsm mentions some sort of "precision fuel gauge" and shows it somehow connected to the fuel rail, but the picture is very vague and I don't see how it's done. Anyway, my reading at the fuel filter pegged my gauge at over 7 bar at idle. Then I cut the ignition and it immediately drops to around 3.8. As of this afternoon what has me concerned is there is so little vacuum going to the FPRs, and it's flucuating or oscilating rapidly between say 12 and 22 cm of hg. But, I have the old FPRs in hand and can apply just a little vacuum and can hear them close when I release it so maybe these don't take much to operate. I also checked vacuum on each cylinder bank, where the line comes to a T, each side was about the same as I had measured at the bank 2 FPR. Anyway, I hope like you say I'm getting close, thanks for the input.
Jeff, first I'm a 550 owner, not a 355 owner, but I think our cars have nearly the same fuel & ignition systems, and I'm curious about a couple points. Don't hesitate to tell me to go back to V12 land if I'm out of line here Since (I think) you have two completely independent fuel & ignition systems with separate ECU's, like we do with the 550, is your LTFT reading the same for both banks (both ECU's?) How do the plugs look on both sides? Do they indicate you're running rich? Have you reset the ECU's after changing the O2's, MAF's, etc. so the LTFT is reflecting the latest conditions? I'm really amazed that you're seeing 7 bar in the fuel system. The Bosch pumps have a pressure relief / bypass valve that relieves (bypasses flow back into the tank) at somewhere around 7-8 bar if the discharge is blocked, in order to protect the pump. Are both sides (both pumps) putting out this much pressure? If you hadn't said you had verified you had fuel in the return lines, I would have said they were completely blocked, with 7 bar on the supply side. I wouldn't think the FPR's would allow much more than 3.8-4.0 bar on the supply side even with no vacuum lines attached, unless there's a blockage downstream of them. But you really need to get a pressure gauge on the fuel rails themselves and see what you're reading there. There are test ports on the ends of each rail where you can connect a gauge, however I don't recall what size/thread the fitting is, sorry. The gauge could simply be a 0-60psi gauge, or possibly 0-100 in your case, if there's a real possibility you have 7 bar there...... I usually use a metal case gauge, which is glycerin filled for these measurements - I wouldn't suggest using a cheapie Home Depot plastic gauge intended for your swimming pool By going back & forth between left & right banks, maybe you can isolate the problem to a particular component?
I am assuming you have a obd2. How old are your 02 sensors? Hve 2 been replaced but not the other 2? Do you have stock or functioning cats?
The LTFT is within 2 % of each other, usually about -23 and -25 at idle. The stats on a short trip usually work out to -18 each side with a minimum of -25 each side. I haven't checked yet, but it's possible that the computer is for the most part able to trim the fuel enough most of the time to not run rich, but I guess since it hits -25 limits, it sets the 1127/1129 codes. I need to check plugs. I've done this several times, I take the car for a short drive, turn the battery off using the factory knob, wait for 20 minutes, start up with no accessories and let sit for 15 minutes. 4 new o2's, I bought the car with tubi test pipes (no cats) Tests performed today: >Vacuum test again on bank 2 just before the white plasic check valve, starts out in 20-22 cm range (shaky needle), then as car warms up, settles to 10-12 cm (4-5 incches). >Un-screwed one of the throttle body test ports, same reading. Checked all test ports were secure. >Verified vacuum line from FPRs where attached to the end of the throttle body vacuum rail. >Verified vacuum line that connects throttle bodies was in place, didn't look cracked. >Sprayed a bunch of carb cleaner to try to find any vacuum leaks but didn't >Removed fuel return line from FRPs one at a time, situated a catch system for fuel and cranked it up. Fuel gushes out, I guess 1/4 gallon in 30 seconds of idle. >Placed my mouth on the return lines and blew through them, took a lot of pressure but after a few seconds I could hear bubbling in the fuel tank. I need to test somehow fuel pressure at the rail, but assuming it's high, I would think I either have too much pressure somehow coming from fuel pump, or a congested (not blocked) return line. Thanks again for all input.
What year is your car and whats your engine number. I would perform a cylinder leakage and compresion test. You need to start with the basics. is the engine sound?
It's a 97 F355 GTS assembly# 24159. It has almost 80k miles. It runs great in my opinion. Good throttle response, good idle, good power - I've had it to 150mph with more left.
OBD2 needs cats, for a difference between upstream sensors and downstream sensors, besides breaking Federal laws. There are many excellent aftermarket and legal choices for cats, and your car will run better with them.* * Don't want to argue, I am trying to help JeffBarber.
Jeff, first apologies for assuming your 355 fuel/injection/ignition was similar to the 550. I now see from the diagrams on Ricambi's site that your 5.2 DME setup is quite different than the 550's 5.2 DME setup. Our 5.2 setup is actually more similar to the 355's earlier 2.7 system in terms of having two completely separate systems for each bank of the engine. Since you apparently only have a single MAF with a single Intake Air Temperature sensor and Coolant Temperature sensor, I'd be inclined to check/replace these two temperature sensors. It wouldn't be the first time that a temperature sensor failed and caused the ECU(s) to stay in warmup enrichment mode. I also now understand that you do not have the test ports on your fuel rails as we do, so it's clear why getting a fuel pressure reading from the rail will be difficult. The fitting on the supply side of our 550 rails is a metric inverted flare, which can be a real challenge to find, much less a pressure gauge tee setup for it. But that 7 bar you're seeing at the fuel filter is really odd. It'll be really interesting to see how this shakes out.
That was Brock (aka Blampee), Mark at Ferrari of Seattle fixed it for him: http://www.ferrarichat.com/forum/showpost.php?p=139890284&postcount=1
I think I may have solved my mystery ... I unscrewed the return line at the bottom of the tank and let all the gas drain out. I then blew into the tank with my mouth and it flowed very easily. I blew up the return line and it did not flow very easily. I detached the return line from the fuel divider and found something I think a previous owner had installed .. a flow restricter! I'll attach a picture of it, I don't think it's stock because I don't see one in this ricambi picture: http://www.ricambiamerica.com/product_info.php?products_id=343568 The 'flow restrictor' has a small hole in the middle so it doesn't completely block. If I remove it I can blow from the FRP to the tank very easily. Now the issue will probably be that I'm not getting enough fuel flow once I remove it. Anybody heard of this item? I'm very relieved it's not general engine issues like rings/valves. Image Unavailable, Please Login Image Unavailable, Please Login
The only application (I know of) where a restrictor in the return line makes "some" sense is where a turbo or a supercharger system has been added to a formerly naturally aspirated engine, and for whatever reason the owner can't properly upgrade the whole fuel system, or the ECU is "locked" and cannot be remapped. In this application, an aftermarket mechanical FMU (fuel management unit) sits downstream of the main FPR and restricts the return, which boosts the fuel pressure at the rail, and the injectors behave like they're larger injectors and will flow more, according to the formula (FPNew/FPOld)^0.5*InjRating. Corky Bell, the famous Texas tuner and author of a couple books on forced induction, used to advocate using FMU's. He also sold them So if your injectors were rated for 300cc/minute, and your new fuel pressure was 7 bar, and the old fuel pressure was supposed to be 3.5 bar, then the injectors would be behaving like (7/3.5)^0.5*300 = 425cc/min injectors (42% larger), and voila, you'd be running pretty rich, unless the ECU was able to pull enough fuel in closed loop to keep the motor running at stoich. So, now that you've removed the restrictor, did you reset your ECU's and take it for a spin? How is your LTFT behaving? Just to ensure the safety of your engine, I would check that you have the right OEM injectors installed before you run it at WOT without that restrictor.
From my experience, Corky Bell always advocated and uses a rising rate pressure regulator. I would be worried about a restrictor getting blown off the end of the return line, and the motor going bad lean.
Rising rate regulator or FMU are different names for the same thing. Corky Bell's company, BEGI, sells both the older type (series 2020) that goes downstream of the OEM FPR, as well as a newer type (series 2030) that replaces the original FPR, and he calls them both either FMU's or rising rate regulators on his website: www.bellengineering.net.
Rain finally cleared up and I get to try it out. I cleared the ECU and let it relearn to stand then walk. Quite wobbly on its feet at first, didn't know what to think about all that lack of excess fuel pressure. I hooked up the EKG (obd software) and took it out for a very gentle ride and as to be expected, LTFT is working it's way back to where it's supposed to be. The mean was -6.8/-8.4 with mins of -8.6/-10.2 on the short 6 mile trip. Everything felt ok, I'm not going to stomp it until its had a chance to really relearn the ranges. Once again, you guys have steered me right and I'm very grateful. I didn't even know what LTFT was until Eric355 pointed it out on my OBD data (I also posted on clubscuderia). Yes, I was just about to give up the ghost on this one. Thanks!! Jeff
p.s. My theory as to why previous owner installed "restrictor" is price of Ferrari FRPs, 1063 bucks each (2 required). Thanks to ff355spider I found them for 160 bucks each. May be posting more help needed next, tbt.
Well congratulations; I'm sure you're feeling pretty stoked about sorting this! It would be really interesting to know why that restrictor was put there in the first place. Perhaps someone felt significant richening of the top end was needed? The info I have for the 550's Motronic 5.2 setup states that it reverts to open loop at WOT or when engine speed is > 4000 RPM, so perhaps the PO wanted it to be pig rich up there, and figured the LTFT and O2 sensors would keep it from being too rich down low. The only reasons I can think of to run it pig rich on top would be: Avoiding detonation Avoiding burnt valves Lowering EGT to avoid damaging the exhaust manifolds? It would be really good to have Dave Helms' input on this.
