Forums/Z31P/z31-repairs-forums engine-mechanical/HELP !! Fuel/boost cut
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Brenton31z: (2018-07-29 07:09:03)
Help is needed, I have done a lot of research and still can not fix this problem.
Quick run down
I have a 1986 z31 turbo was originally auto previous owner converted to manual and removed aircon. I am getting fuel/boost cut when ever the car hits positive boost. I have replaced all vacuum lines thinking this would be the problem. But no so
I have done a code check and codes 13,23,24,31,41
I have fixed code 13 with new C/T sensor and replaced the harness. Code 23 I have tested the continuity on the TPS and it reads fine I move throttle cable a little and it opens. (Do I still need to replace ?)
Code 24,32,41 Iâm not worried about as code 24 would be because of the auto to manual conversion code 32 I donât have aircon and 41 I have after market fuel pressure gauge.
I am lost where to go from here, all I can think is to replace the ECU but I just donât want to be spending money for no reason. I do smell a little burning smell from ECU but apart from that I really donât no. I re-ran codes and code 13 has gone after fixing but all others stay.
Any help would be much appreciated
FrozenZ: (2018-07-29 20:52:20)
I'd 1) check the FPR and maybe just replace it, and 2) try rolling with the TPS unplugged and see if that helps (you might have a rich, stumbly idle and light backfires if you come all the way off the throttle suddenly but drive better otherwise.) If it's the TPS it doesn't have anything to do with going into boost, it's either just badly adjusted or hosed and happens to think that you're coming off the gas when you're actually dropping the hammer.
Brenton31z: (2018-08-02 09:22:05)
Okay thank you, new FPR on its way
Brenton31z: (2018-08-06 06:13:45)
Just an update I have replacedfpr and still has not solved the problem. Any ideas would be amazing
FrozenZ: (2018-08-06 20:43:54)
Did you try unplugging the TPS?
The thing is, the ECU has no way of telling when you go into boost (the "boost sensor" is just for the dash, the car is just tuned for the stock turbo and stock PSI), so if your issue really is related to going into positive boost there's not that many things it could be. When you hit the "cut" what does your fuel pressure gauge say? (Did a PO put that on?)
Brenton31z: (2018-08-07 00:27:33)
I unplugged the TPS and I still get the cut. The fuel pressure gauge is under the hood so I wouldnât be able to tell you Iâll have to try work out a way to read it while I drive. It does not cut when just sitting in neutral only when it is under pressure (driving)
Brenton31z: (2018-08-07 00:32:28)
I have read spark plugs can be the problem so will be replacing them this arvo
Brenton31z: (2018-08-07 06:48:12)
Spark plugs replaced and still no luck. Iâm so lost at this point
FrozenZ: (2018-08-07 10:26:40)
Stop throwing random parts and effort at it and look at one problem at a time. You think you have a fuel cut under load but you can't actually tell for sure. If your MAF, harness, and ECU are OK (don't start replacing those yet) there's only a few ways ways for that to happen, the TPS circuit, or you have a bad fuel pump that' only puts out enough pressure for light load and then you just don't have enough fuel later. The fact that there's already a gauge under the hood makes me think that the PO was trying to solve the same problem you are. When the car's cold, get someone to turn the key to ON while you watch the fuel pressure gauge. It should jump up to the high 30s PSI. Does it?
Brenton31z: (2018-08-07 20:36:03)
I replaced the fuel pump when I first got the car as it wasnât working replaced with a walbro 255. I also installed a 30amp rely fuse for the fuel pump. The fpr reads 60 psi when tuned on from cold and sits at 48-50 when running
mwolvinm: (2018-08-08 17:27:14)
That's a bit on the high side. Could it be getting too much fuel?? What did the spark plugs look like when you pulled them?
Brenton31z: (2018-08-08 20:25:42)
Thatâs what I thought as well after looking up stock presser so I set to stock, when vac hose is taken off presser goes up and when on wot presser goes up so all that works. But still getting the cut. The old spark plugs were black very black
FrozenZ: (2018-08-09 00:10:21)
Not surprising you've got black plugs and it's running like shit when you're giving it like two-thirds more fuel than stock. The z31 ECU is tuned really rich to start with so you may just be flooding out the motor when you get under load. Leave the pressure at stock and change your oil because it's probably full of gas now. Setting up something so you can check fuel pressure while you're driving will make this a lot easier. (My personal experience is that most reasonably priced aftermarket FPRs are absolute shit and are not doing what you think they are lol.)
Brenton31z: (2018-08-09 08:49:33)
Okay guys latest update. I zip tied my phone into Engine bay to watch the FPR. The reg shows it is not a fuel cut it builds pressure up to 38-40 psi under load then when I hit this boost cut it drops back to around 30 psi.
I will be dropping oil this weekend. Thank you all for your help so far. So now I no itâs a boost cut any ideas ?
mwolvinm: (2018-08-09 16:53:40)
Okay guys latest update. I zip tied my phone into Engine bay to watch the FPR.
LOL. This sounds like the lead in to a bad joke…
___
So, you have an aftermarket FPR and fuel pump, correct? Any other mods? Do you have a (known good) stock FPR on hand you can put in the car and check to see if it's doing the same thing?
Brenton31z: (2018-08-09 20:53:57)
Correct They are the only mods. I just replaced the fpr the PO had in there with a turbosmart 800
Brenton31z: (2018-08-09 20:55:22)
I donât have a stock fpr
Wilsonthesphere: (2018-08-10 20:40:57)
Other than the fuel cut the car idles and run fine in vacuum? Have you checked the POV? I would just put a cap from the NA or pipe fitting if possible.
Brenton31z: (2018-08-11 07:44:10)
Car runs fine at idle, I removed the POV and capped Iâm still getting this cut. I donât no what else it could be
JSM: (2018-08-11 14:36:23)
Iâm more curious about your symptoms. When you say cuts out and no longer makes boost, does it seem like it just stalls or shuts down or does it continue up into the rpm range and just not make power? I was thinking maybe your waste gate was stuck open. Can you rev the engine under no load through the rpm range? Just blipping the throttle?
Ive seen many rusty wastegate arms and was wondering if it may be hanging up some.
Brenton31z: (2018-08-11 20:58:26)
it just stalls and shuts down but the car does not turn off, once it comes back off pressure/load it will run again. I can rev the engine under no load through the rpm range and it is fine.
Wilsonthesphere: (2018-08-14 14:11:27)
Are you sure your ignition system is in good shape. Good coil and good spark plugs and wires?
mwolvinm: (2018-08-14 17:25:55)
Iâm thinking it is fuel related based on the pressure readings from the gage. Could there be a restriction in the fuel line somewhere that restricts flow? Iâm thinking a crushed fuel line, clogged filter, or gummed up sock in the tank.
My my thought is that you arent getting the flow you wed to the injectors to support the fuel needed on boost.