Jersey Posted July 31, 2003 Share Posted July 31, 2003 Having a strange problem. For some reason, my '73 with the L28ET doesn't want to hold an idle anymore. I just BARELY does...sometimes, other times it stalls when coming to to a stop. Just started happening out of the blue. Hg's on the vac gauge are now reading less at idle - like 18Hg and when i take the valve cover cap off, it really doesn't make a difference like it used to. Yesterday, i pulled a plug off one of the unused intake ports that i had capped off and the idle came back up to 800rpm and the Hg's of vacuum jumped back to the original 21hg. Idles fine like this. Strange that if i create a vac leak in my intake that it jumps up in idle and increases vac pressure. It does smell rich when this port is plugged so i'm figuring there's not enough air getting to the intake to mix with the amount of fuel supplied and when i allow air to enter the intake by unplugging an unused port, it creates a better mixture and runs better. I had a new PCV and tried that but it made no difference. I also checked fuel supply and return and it's pumping fine. Also checked return line for plugs - fine, and FPR for correct operation - fine. Any ideas why this would just start happening? Nothing was changed between the time it ran and idled perfect. It seems the amount of air passing by AFM and being monitored is not the same amount of air getting to the intake. Then i thought maybe the I.C. pipe or the I.C. itself created a leak but, it would still be able to pull the air through the leak to supply the intake and, boost is fine. I'll list my setup. Thanks in advance for any ideas. '82 L28ET stock injectors stock FPR Walbro pump no pov no aac no aic no vcm no egr 1G DSM BOV stock T3 threaded wga arm small NPR I.C. stock ignition stock T.B. Quote Link to comment Share on other sites More sharing options...
Lockjaw Posted July 31, 2003 Share Posted July 31, 2003 If you are using the stock AFM, there is a little round plug about 1/4 inch on the plastic cover side. If you drill a small hole in that and pop it out, there is a screw in there that lets air bypass the door in the afm, and you may be able to "tune" your idle a little. Sounds like you have eliminated all your idle control stuff, and in reality, that is how the system controled idle, by adding extra air. You can also raise the idle at thr TB, its up to you. FWIW, mine is doing the same thing, and I had an 1100 rpm idle, added my cam, and it dropped. So I need to work on that. It dropped off when coming off the interstate, and sometimes stalled out. It is irritating for sure. Quote Link to comment Share on other sites More sharing options...
Jersey Posted July 31, 2003 Author Share Posted July 31, 2003 Thanks for the quick respose Lock. I am using the stock AFM. I do know that i probably could start adjusting other things (ie - AFM) to correct the problem i'm having but, i'd rather figure out why this just started to happen all of the sudden and find the cause rather than cover up the problem but adjusting other stuff to compansate for it. I did eliminate all my idle control stuff and it ran perfect - idled 800rpm smooth and pulled through the gears strong for months. It seems to me, since pulling the valve cover cap off doesn't make a real difference now, that somehow the air isn't flowing throughout the motor correctly. Can't remember if there's a valve on the crank breather that might be plugged? hmmm... Quote Link to comment Share on other sites More sharing options...
fl327 Posted July 31, 2003 Share Posted July 31, 2003 Whats up Jersey, Did you per chance check that rubber boot off afm, maybe it has some small cracks in it? Also, maybe one of the fittings is loose and leaks a little air there as well? Bypass hose off the BOV maybe? BOV flange? How is the power? Feeling a little slugish maybe? Do you stall in between hard shifts sometimes? Really sounds like you have an air leak somewhere, especially when you said that it likes to stall coming to a stop. I do not think it is the AFM. Have you tried spraying carb cleaner to see where idle jumps and pinpointing the leak. Also, you may have a leak from the intake manifold, causing you to stall when coming to a stop or idling in place. Quote Link to comment Share on other sites More sharing options...
Jersey Posted July 31, 2003 Author Share Posted July 31, 2003 Hey 327. I did a quick inspection of the AFM to T3 boot and it looked fine. I will try the carb cleaner trick. Fittings are all secure and tight. Checked em. BOV flange and bypass hose not leaking - checked. Power seems up to normal, no problems there. I was thinking the same - intake manifold gasket leak but then again, why when i create a intake manifold leak, the motor runs correct - back up to 800rpm with no loping of idle to eventual stalling condition? And why wouldn't it make a differrence in idle now when i pull the cap off of the valve cover off? I have a feeling you are thinking in the right direction - a leak between the AFM and T3. I think if the leak was here, it would create the problem i'm having. Any place else after the T3, it would be able to pull enough air to supply the intake, even if there was a leak. Thanks for the input 327. Quote Link to comment Share on other sites More sharing options...
Guest bastaad525 Posted July 31, 2003 Share Posted July 31, 2003 hmmmmm I wouldn't think it is a vacuum leak only because as you stated, CREATING a vacuum leak yourself causes the problem to alleviate. Sounds like you are running way too rich at idle and possibly only at idle, since you're saying power is good off idle. I had had strange problems like this in my N/A zx... it was problems like these that at one time made me glad to switch over to SU's. I'm willing to bet it is more likely an electronic problem than a vacuum leak. Maybe your TPS? Do you have a voltmeter? If you can, test all your sensors. Everytime my ZX would develop strange problems outta the blue it ended up being one sensor or another. I actually found this out the first time accidentaly... the car had suddenly started to run pretty bad, off idle it would stumble horribly... so I was checking everything under the hood making sure all connections were clean, and forgot to reconnect the TPS... went for a test drive and the car ran perfectly! Reconnected it and of course it was back to running crappy. This did not pinpoint the TPS as the cause of the problem (in the end it was not, it was my head temp sensor) but just put the car into closed loop (or maybe it is open loop... I always forget which is which) which basically shuts off inputs from some of the sensors. Anyway it's a test you can try, might help you figure out if it's EFI related and keep you from chasing vacuum leaks you might not have. Quote Link to comment Share on other sites More sharing options...
Jersey Posted July 31, 2003 Author Share Posted July 31, 2003 I will double-check all sensors with my meter. Thanks 525. Quote Link to comment Share on other sites More sharing options...
Len Posted July 31, 2003 Share Posted July 31, 2003 Jersey Don't know what the weather is like over there in "Jersey" (didn't do that on purpose) but when this happened was there a temp change? Did it get warmer? Meaning less oxy in the air causing car to run rich? Just a thought. I know at the dragstrip with all the carbon monoxide in the air, no wind. My car along with a few others run richer. Also I tried removing my vac. booster on top of intake that runs across to idle control for my air conditioner. Outcome;bad idle. I then reinstalled it. But I have air conditioning; so you may be able to run your car without it. Quote Link to comment Share on other sites More sharing options...
Jersey Posted July 31, 2003 Author Share Posted July 31, 2003 No, it's been the same here Len - 75-80deg. Actually a little cooler than the previous weeks which were high 80's, low 90's. Thanks for the thought though. Quote Link to comment Share on other sites More sharing options...
Len Posted July 31, 2003 Share Posted July 31, 2003 Boy your fast I just edited my post and you had already replied! Quote Link to comment Share on other sites More sharing options...
Jersey Posted July 31, 2003 Author Share Posted July 31, 2003 No vac booster installed. Never had a problem before without it and haven't made any changes since. Strange eh? You're fast yourself Len Quote Link to comment Share on other sites More sharing options...
Afshin Posted August 1, 2003 Share Posted August 1, 2003 Hi Jersey, I had a similar experience where the car suddendly started to idle terribly and even stall at idle. However it still drove quite well with good power when on the throttle. I also had noticed decrease vacuum at idle. I thought it would be a vacum leak but was not finding anything at first and then realized that I had a leak between the AFM and turbo (was difficult to see), I know you inspected it once, but I would inspect it again very closely. However, I'm not sure if this would explain why the car runs better when you create a vacuum leak. Another thing that comes to mind is a poor connection from the head temperature sensor, it's common and I believe would cause the car to run rich and idle poorly, which would improve with unmetered air entering (vacuum leak). Good luck Quote Link to comment Share on other sites More sharing options...
Jersey Posted August 1, 2003 Author Share Posted August 1, 2003 Thanks Afshin. I looked and checked the boot between the afm and T3 last night as closely as i could with the limited time i had and didn't find any leaks. I really need to pull all the I.C. piping off and anything else that's in the way and remove the boot to make sure. I also checked and cleaned the connections for the Throttle Body Switch (?) and it tested ok. I pulled the Head Temp sensor off and cleaned it's contacts as well but didn't have a chance to test as per FSM but i will this weekend. Thanks for the suggestions. Quote Link to comment Share on other sites More sharing options...
Len Posted August 1, 2003 Share Posted August 1, 2003 Did you change your timing since this happened? Reason why I'm into this subject is because last year I had that problem too. I really don't know what fixed it for me. Since I changed my afm to turbo boot redid connections on temp sensor. Installed new injector connectors. adjusted my timing. Re soldered all the splices I had where ECM ties into harness (I did that because sometimes car would run ratty accelerating till I wiggled plugs connecting my ECM). Good Luck Len By the way my Idle is real low when air conditioning on but bearable. Runs fine with air conditioning off. Quote Link to comment Share on other sites More sharing options...
Jersey Posted August 1, 2003 Author Share Posted August 1, 2003 Checked the timing last night - still sitting steady @ 20btdc. Thanks Len. Quote Link to comment Share on other sites More sharing options...
Guest bastaad525 Posted August 6, 2003 Share Posted August 6, 2003 did you ever figure out what the problem was Jersey? Quote Link to comment Share on other sites More sharing options...
Jersey Posted August 6, 2003 Author Share Posted August 6, 2003 Nope, not yet. Shoot, i have your "lag/stumble" problem on my mind! haha. I really haven't had "garage" time lately and with all this rain here in NJ, i've just been driving my truck around. I just got back in from the garage (2:19am) Checked for leaks, none. Vacuum on gauge still reads 19hg and runs poorly and VERY RICH at idle. It actually burns my eyes when i'm under the hood...with F.I.!! ha! When i used to tune my SU's, i used to get the rich/eye burn but i never figured i would with a closed F.I. system! My luck i guess. If i pull a capped plug off one of the intake ports and create the vacuum leak in the intake, idle comes up to 800rpm, vaccum increases to 21hg, it runs less rich and idle smooths right out. Go figure. Checked and cleaned all harnesses, no help. Checked O2 and harness with meter, working properly. Good readings. Only thing i can think of right now is valves. I think that'll be the next thing i look at and check. Everything electrical and hose-wise in the engine bay seems to be fine. Either i'm completely missing something or it's under the valve cover...or even worse, inside the cylinders, like rings, causing low compression. Quote Link to comment Share on other sites More sharing options...
Guest bastaad525 Posted August 6, 2003 Share Posted August 6, 2003 I'm still thinking it's something electrical. If it's running really rich at idle, it might be your TPS has gone bad or out of adjustment. If it's not reading in the 'off' position at idle, the injectors would be dumping too much fuel in there. With a properly working and adjusted TPS, you should notice the idle change when you disconnect and reconnect it. Try that. Quote Link to comment Share on other sites More sharing options...
Forrest Posted August 6, 2003 Share Posted August 6, 2003 Have you checked your fuel pressure? With the engine off, pump running, at idle, and while revving? Quote Link to comment Share on other sites More sharing options...
Afshin Posted August 6, 2003 Share Posted August 6, 2003 Well as you describe if your car is running so rich and corrects with creating a vacuum leak I think it is less likely to be a major engine problem since a problem with rings or valves should not correct so easily with creating a vacuum leak or necessarily cause the degree if richness that you are describing. I also think it's less likely to be the TPS since I have never found the unit to cause such a drastic difference in idling (my car idle barely changes with unplugging of the TPS). Off course I am wrong quite often and checking compression and TPS are clearly worthwhile. Here is my list of more common (not all) reasons for a Z to run very rich: -Faulty head temperature sensor unit or connector. -Faulty connection of harness to ECU (unplug you ecu harness, spray with cleaner even if it looks clean and snap back on) -Increased fuel pressure, have you checked the pressure, that could also cause some leak at injectors or rails causing the gasoline smell you have from your closed EFI system. -Faulty air flow meter or connector (again at either end i.e. AFM or ECU connector), check the flap on the AFM if you already have not for smooth opening... also try and see if the car runs better with you pushing the AFM flap just a tad more open (without the vacuum leak). Keep us posted. Quote Link to comment Share on other sites More sharing options...
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