evildky Posted April 16, 2004 Share Posted April 16, 2004 ok, I have a 71 with an 82 L28ET swapped in, I am using fuel lines from a 78 and have fuel supply coming from the drain hole, so it should get plenty of gas, the car was running fine the other day, it ran a 13.6 at Gainesville a coupla weeks ago, now all of a sudden it runs like crap, the problem ocours at the transition from vacume to boost, only when the engine is loaded, idles and rev's fine, but when I start to accelerate even slowly, I can watch the guage slowly loose vacume and just when it gets to zero it'll start bucking and dying when it bucks the boost goes up to around 5psi then it kinda dies and once it hits zero it'll surge again, I have tried bypassing the fuel pressure reg(just pulled and pluggged the vac line going to it), made no difference I thing my O2 sensor is going casue my A/F guage alwasy shows a bit to the lean side and it just started going down till it fell off to no reading at all, and with 55psi of fuel I doubt it's lean, and the exhaust smells rich what am I missing? could a bad O2 casue this ? Quote Link to comment Share on other sites More sharing options...
evildky Posted April 16, 2004 Author Share Posted April 16, 2004 aw C'mon someone has to have some clue ? I am stumpped seems to be one problem after another I am tempted to fix it sell it and get a TT Quote Link to comment Share on other sites More sharing options...
Guest bastaad525 Posted April 16, 2004 Share Posted April 16, 2004 O2 sensor wouldn't affect your car that badly. Fuel pressure regulator could do that if it's sticking and isn't opening enough to supply enough fuel when boost comes on, but I dont think it'd be that dramatic, just a gradual leaning out as pressure in the manifold went up but fuel pressure was not increased. Disconnecting it wouldn't affect the problem one bit though so is not a good diagnosis. This sounds like the same problem that is so common to so many of us at various times. 9 out of 10 times it's simply caused by bad or dirty connectors. Get to the auto parts store and pick up a large can of electrical parts cleaner spray. Disconnect all the wires from your ECU, AFM, TPS, head temp sensor, CAS, and spray all the connections. Might be a good idea to spray the injector wires as well but they're kinda a pain in the ass to get to so i dont usualy bother. Let everything dry off and plug it all back in, plug the ECU back in last. I had this exact same problem about two weeks ago and it turned out some water had gotten into the connector on the AFM. It would run fine up to almost exactly 0 vacuum/boost pressure and as soon as it started to get into boost it would start bucking and felt like it wanted to stall. A good tip that was given to me as well is after cleaning everything off to put some dielectric grease on all the connectors, helps to keep the clean and to keep from corroding. Let us know what happens! Quote Link to comment Share on other sites More sharing options...
evildky Posted April 17, 2004 Author Share Posted April 17, 2004 I have some dielectric grease and I'll try it but, I think it has something to do with the boost, be it the wastgate or turbo or whatever else, because it happens at the transition from 0 manifold pressure to boost, runs fine with vacume, but ones manifold pressure reaches zero it does not want to go into the boost zone, and it'll sputter and surge to about 5 psi then kinda die only to surge back up to 5 psi my logic is that the ecu dos not know if the manifold is under vacume or boost, there is no electrical sensor to tell ti wat the manifold sees, I am running the stock ZX fuel pump wired via a relay, and a MSD boost referenced fuel pressure regulator<-installed brand new a coupla weeks ago, I still have the old FPR si I can try switching it back just to solidly eliminate it as the source of the problem but I really appreciate the imput, just need fresh ideas to keep me thinking, I stare at a problem sometimes till it drives me nuts Quote Link to comment Share on other sites More sharing options...
Guest bastaad525 Posted April 17, 2004 Share Posted April 17, 2004 Dude TRUST me I had the EXACT SAME PROBLEM and it just ended up being some water in my AFM connector. The car was running perfectly fine just cruising on the street, then I went to get on the freeway and tipped in the throttle more and as soon as boost came on it felt like it was being fuel starved, bogging and sputtering... let off enough to get back into vacuum and it ran PERFECT. Several times I gradually fed in throttle and every time right about the exact time the boost needle would hit 0-1psi of boost it would start surging like that and would get worse and worse if I kept adding boost. I nursed it to a gas station, and started checking all my connections. I saw like ONE MEASELY drop of water inside of the connection to the AFM. Used some electric parts cleaner spray on the AFM and ECU connectors, let it dry, put it all back together, and the car ran PERFECT after that. It didn't matter that the ECU has no way to measure boost as you say. Dont just try the dielectric grease, clean off all your connectors first. You'd be surprised at how many times this simple thing has fixed odd running problems for me and many of the other guys here. So try that FIRST it's easy and cheap, before going thru lots of hassle. I'm sure the MSD FPR is working fine. How are you liking that by the way, assuming of course it isn't causing this problem? I've been meaning to pick one up for months now... will probably order it this week. You just can't beat the price... I've been telling everyone about them. Get yours from Overboost.com? Anyways, if it turns out not to be electrical, then go ahead and try the stock FPR again, and if that doesn't do it I would strongly suspect a boost leak. Quote Link to comment Share on other sites More sharing options...
evildky Posted April 22, 2004 Author Share Posted April 22, 2004 it took me a while to get time to mess with the car, I cleaned everything the other day and it did seem to help, I just went up the road a bit and it did build boost so I out it back up, tried it again today and it is back to the same problem, I cleaned the contacts and added some die electric grease, seemed to help some it would get a little boost then surge, found my hose on the turbo was a bit loose, tightened it took it out and it was surging at zero manifold pressure again, I tightened everything up, adjusted the afm, still bogging, so I disconnected the knock sensor still does it, checked the turbo for play or resistance, felt ok to me, this thing is driving me nuts one thing I noticed it that when cold my A/F meter reads iseal, once warmed it shows lean? and it seems to behave much better when cold but still acts up, just gets worse with the engine warmed up, I am really wanting an SDS system, if only I could afford it Quote Link to comment Share on other sites More sharing options...
Tim240z Posted April 22, 2004 Share Posted April 22, 2004 Sounds like a bad MAP sensor? Quote Link to comment Share on other sites More sharing options...
wigenOut-S30 Posted April 22, 2004 Share Posted April 22, 2004 Could you possibly have a boost leak? like a cracked or torn boot? sounds like you are running lean all of the time as well.. and when you get into boost there is not enough fuel and the motor is dying.. could it be your fuel pump? or clogged fuel filter limiting the fuel?? What all have you done to the Z.. 13.6 is awsome with only 8psi of boost.. I hope you get it figured out soon. Quote Link to comment Share on other sites More sharing options...
evildky Posted April 23, 2004 Author Share Posted April 23, 2004 I have tightened every hose and dohickey on the intake as well as the j pipe at both ends, if there is a boost leak I can't find it, I might try changing the fuel pump as I have a new msd sitting in my garage I planned on adding later any how, as for the 13.6 my car is an early 71 so it was one of the lightest cars to start with, the interior is gutted, just a dash and 2 corbeua seats, no heatercore blower fan or any thing like that, I am guessing I weigh around 2200lbs? I turned the boost up to 8 psi with a bleedoff style boost controller, am using an MSD boost referenced FPR #2222 (which I got from summit about the same cost as overboost) at 55psi (you have to remove the locknut to get it up that high) and a L24 damper, other than that it's a 180K junkyard motor, oh yeah, 2.5 crush bent exhaust no muffler that pass was made with drag radials, that run had a 2.1 sec 60 footer, I was making 1.9 earlier that morning, with drag slicks and the origional L24 it pulled a 1.6 60 footer last year, but the et was like 15.9 Look for my car in the august issue of Grassroots Motorsports Magazine, it was in the challange (for the second time), it's primer grey, #13 Quote Link to comment Share on other sites More sharing options...
Guest bastaad525 Posted April 23, 2004 Share Posted April 23, 2004 Odd that cleaning the connectors seemed to help but didn't help for long. I'm still convinced it is something electrical. Maybe some of the wiring is loose or there is a break or a wire grounding out or making contact with another wire... something... unfortunately once you get past the usual easy stuff, with the EFI things can really get complicated trying to find what is causing the problems. I've gotten rid of two stock nissan efi systems now because of gremlins that I just couldn't seem to solve no matter what I did or who I took it to. About the fuel pressure... interesting that you turned it up so high. For one, the stock EFI should be able to handle 8psi of boost on just stock fuel pressure completely safely. For two, I would think that the increased pressure might send a stock fuel pump to it's early grave. And for three, I'd be surprised if it wasn't causing your car to run badly, at least during regular cruising. On my built N/A motor, 4psi was enough to make it go from severe detonation above 4000rpm, to running juussssssssssssssst right. 6psi increase was enough to make it stutter and stumble at idle and low RPM (of course you can just compensate for that with the AFM). Before you started having problems, what kind of air/fuel ratio were you getting at WOT at 55psi? Say, above 5000rpm? I'm actually going to install that same MSD regulator and am looking for a good baseline to increase the pressure to that will increase my safety margin and power level above 5000rpm, w/o being detrimental in any way. I was thinking more like 40-44psi (at idle with the vacuum connected). 55 seems high but if you were getting good results I may try that as well. Oh and the early 240's were very light with full interiors... I'm guessing you mean 2200lbs with you in it? I think the original 240's weighed 2100-2200 stock... man I wish I had one of those Quote Link to comment Share on other sites More sharing options...
evildky Posted April 23, 2004 Author Share Posted April 23, 2004 I have cleaned every connector, I have a new afm on the way, and I already have a spare ecu I will try swapping them next, the wire harness should be fine, it came out looking good, and I have not done anything to it other than the necesarry mods as for the fuel presure, I was reading lean at idle and when running down the strip I never even looked at it, I need to move it to the A piller so I can see it better, I just started turning it up till the throttle tip in seemd eager with no hesitation, same set up I made my 13.6 pass with also the fuel rail and intake will be replaced soon, once the spare intake arives I'll be shaving it of all the useless crap, and I made a billit fuel rail that I plan to install at the same time, I guess I just keep replacing parts till it works ? Quote Link to comment Share on other sites More sharing options...
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