jmt Posted February 27, 2008 Share Posted February 27, 2008 Hi everyone, im new here just picked up a 76 280z that hadnt been started in 2 years. Ive been through the manual, the efi guide and lots of posts. I have plans to restore this car, but would like to get it up and running to par before tackling some body rust. I do have it running and driving. The reason it was parked was because it kept fouling plugs. I replaced the plugs with NGK gapped .040 and found the coolant temp sensor was faulty. So I tagged it this morning and took the day off to waste some gas and see what needs work first aside from the body. Heres what I found: The Z runs good up until around 4k and at this point spits sputters and doesnt want to rev any higher. If I rev it slowly it will rev to redline but cracks like fuel starvation. Ive replaced fuel filter and fuel line attached, checked all connections and unplugged each injector. It stumbles so I can tell each one is firing. AFM seems to be working fine, checked TPS, checked vacuum lines and replaced any that were suspect. What else can I check, without dumping hundreds in injectors or a pump. I have run one can of seafoam through the tank. Any help is appreciated since fun doesnt begin til 4k. Thanks Josh Quote Link to comment Share on other sites More sharing options...
jmt Posted February 29, 2008 Author Share Posted February 29, 2008 Played with it some tonight. Im hesitant to drop the pump to see if there is a filter in it...can anyone confirm this? Also it really seems to be running terribly rich...I smell like fuel after being around it for a few minutes, and it puffs a cloud if it sits and idles for a while. Kindof like its loading up. Any insight here? Anyone??... Thanks Josh Quote Link to comment Share on other sites More sharing options...
cybermecium Posted February 29, 2008 Share Posted February 29, 2008 Check valve clearances and adjust if necessary. Quote Link to comment Share on other sites More sharing options...
m4xwellmurd3r Posted February 29, 2008 Share Posted February 29, 2008 check the water temp sensors wires. those corrode easily and cause overly rich issues. Quote Link to comment Share on other sites More sharing options...
jmt Posted March 1, 2008 Author Share Posted March 1, 2008 Ok heres what I learned tonight so far. Did a compression test: 150 psi +-5. I did it cold so results are probably a tad low. When I pulled the plugs, I found 1-5 looked ok a little black but ends were tan, but 6 looked black as coal. Not sure where to go from here. HELPPPP! Thanks Josh Quote Link to comment Share on other sites More sharing options...
blue72 Posted March 2, 2008 Share Posted March 2, 2008 I had the exact same problem. Anything over 1/4 throttle and it won't rev above 4k, but under light throttle it revs all the way. Then driving around under load it would stumble occasionally, and generally not run like I wanted. It turned out to be my distributor. I replaced everything, even swapped the motor (not because of this problem, just for more power), etc... but when I switched to a ZX dizzy with the E12-80 module it fixed all of those symptoms and I have had a big smile on my face since. Quote Link to comment Share on other sites More sharing options...
sweetleaf Posted March 2, 2008 Share Posted March 2, 2008 What's your fuel pressure at? Quote Link to comment Share on other sites More sharing options...
Careless Posted March 2, 2008 Share Posted March 2, 2008 the fuel pump in the 76 has a small screen filter at the inlet. here is what i did to fix my non-starting problem. I took apart the pump, tried to take the screen out by using a short but wide screw, and threaded it into the plastic that held the mesh, so I could pull it out using a pair of pliers. It didnt come out, and I'm not sure if it should, so I left it and cleaned the inside of the pump with 400 - 600 grit sandpaper, polishing all the surfaces of each one of the dowels and the gear inside as well. Then I bought two o-rings that were the same size as the teardrop ones that were in the pump, and squeezed them to fit. (this was the problem with the pump in the first place, it wouldnt turn because one of the o-rings somehow slid out of its groove and lodged into the gear and stopped it from running. So after I fixed that, I bought new plugs. and it seemed to start right up. Try putting back one of the old plugs into number 6 and see if it runs a bit better. But cleaning out the pumping mechanism in the pump itself might be a good idea, and it ain't that hard at all. including the sandblasting of the outside of the pump which I did afterwards once I covered the in/outlets... I'd say it was a total of 1.5 hours of work. Quote Link to comment Share on other sites More sharing options...
jmt Posted March 2, 2008 Author Share Posted March 2, 2008 I pulled the lines off the tank today and checked the pump, its a aftermarket style with no strainer (that I could find) built in it. Gas poured out of the tank so I think im good there. Im going to check the fuel pressure after I go buy one tomorrow. Im really stumped. I also did a plug chop. For those not familiar thats where you put it to the rpm you want to check which in this case is 4k and cut the ignition. Plugs were white...so lean, so I think I can rule out a ignition problem...I THINK! If it were ignition problems the plug would be wet from fuel with no spark..am I on the right track? Quote Link to comment Share on other sites More sharing options...
jmt Posted March 2, 2008 Author Share Posted March 2, 2008 Ok checked my fuel pressure, it spikes to around 40 when I floor it then settles back to about 34 psi at all rpms. Also replaced coil with accel just for peace of mind. Also checked valves which are within spec. I guess im down to injectors? My plugs were really white tonight after a drive. Could a loose valve cover introduce a lean condition? I wouldnt think so..buttt... Quote Link to comment Share on other sites More sharing options...
jmt Posted March 4, 2008 Author Share Posted March 4, 2008 Anyone have any insight here? Is there anything that would cut my fuel out in the higher rpm range aside from clogged injectors? its just really getting me because all the plugs are ghost white. !ts just hard to believe theyre ALL clogged. I do have different colored injectors though. a couple tan ones a couple brown, and one green which is a turbo injector i think...help please Quote Link to comment Share on other sites More sharing options...
2savage Posted March 4, 2008 Share Posted March 4, 2008 What about the crank angle sensor? If that is bad the computer will have a basic map for firing each cylinder but this is conservative, to protect the engine, when the CAS malfunctions. It will get you home but that's it. You need a functioning CAS to get full power. Quote Link to comment Share on other sites More sharing options...
jmt Posted March 5, 2008 Author Share Posted March 5, 2008 While I appreciate the thought... I dont believe my year model has a crank sensor since im not run off of coil packs. Thanks though...definitely need all the thoughts I can get. Hey blue72, did you ever check your plugs to see what they looked like?...I would definitely chalk it up to spark cutting out, but my plugs tell me that im not fueling.. Quote Link to comment Share on other sites More sharing options...
jmt Posted March 8, 2008 Author Share Posted March 8, 2008 Well, I replaced the injectors and all associated rubber lines last night...WOW what a night and day difference. It revs up to around 5k now. This fixed about 90% of my problem.... Now I feel like my timing may be off. Im going to work on my distributor today. I think I have a points setup, if so it may be time for an upgrade. OK while I was driving tonight, I in neutral I can go straight to redline no problem, but when im driving I get stopped at 5k. Can this be timing related or what am I missing here...im out of ideas. Please help.... -Josh Quote Link to comment Share on other sites More sharing options...
m4xwellmurd3r Posted March 9, 2008 Share Posted March 9, 2008 just out of curiosity, how does it run when you unplug the TPS? on my Z because of the issues it was having, the TPS was making it run worse (bad injectors, wrong afm, etc) unplugged it and it ran like a dream. of course, now that i've got it all fixed i need to plug it back in and adjust it. Quote Link to comment Share on other sites More sharing options...
jmt Posted March 10, 2008 Author Share Posted March 10, 2008 just out of curiosity, how does it run when you unplug the TPS?on my Z because of the issues it was having, the TPS was making it run worse (bad injectors, wrong afm, etc) unplugged it and it ran like a dream. of course, now that i've got it all fixed i need to plug it back in and adjust it. Hey bud, ive had a breakthrough!!! After you posted this message I got curious. I was at the inlaws house and decided to unplug the tps for the ride home since it was a 65 zone and I could wind it up a bit. I can actually rev into redline with it unplugged! I guess this means im fueling rich on the top side. You can definitely tell its unplugged since it idles funny and it doesnt rev fast on the upper rpm range but it does rev! Ok so what would be my plan of attack on this? I understand how the tps works but its just a fuel enrichment... need some help on this one!!! Thanks again for everyones help thus far. -Josh Quote Link to comment Share on other sites More sharing options...
jmt Posted March 12, 2008 Author Share Posted March 12, 2008 Ok, tonight double checked over everything. Replaced connectors on water temp sensor. Got the meter out and followed the "bible" to check all the efi components to no avail. I drove it tonight and plugged in and unplugged the throttle switch with the same results. I can get to redline without it plugged in, but if I plug it in 5k is all she wrote. I just dont understand what it could be. Plugs are still white. I understand newer efi alot better since I was a ford sho fanatic for years. But this as simple as it is is mind boggling to me. Anyone got anything? Anything at all?? -Josh Quote Link to comment Share on other sites More sharing options...
Careless Posted March 12, 2008 Share Posted March 12, 2008 tried a different/new tps yet? Quote Link to comment Share on other sites More sharing options...
Daeron Posted March 13, 2008 Share Posted March 13, 2008 man, I wish I had read this thread two weeks ago. the throttle position switch only has three states.. "idle," "cruise," and "WOT." When the computer isn't getting a signal from the TPS, it presumes "cruise" mode. "Idle" is less fuel, and "WOT" is more fuel. It is MUCH simpler than the potentiometer-style throttle position sensors used one more modern systems. I had the exact same, high-throttle cut-out anytime my engine bay got wet, because the boot on the TPS plug was bad and it shorted the entire affair out. It took me several recurrences of this problem before I definitely isolated the issue; since then, any time it recurred it was only a two-minute fix. The cover for the switch should be removable with some work; its a very elementary device and it may be that any defect would be apparent and repairable. Or you could just source a new or JY unit. Have you tested the function of your TPS as described in the EFI bible? If the switch is verified good, then the remaining issue is almost certainly in the wiring associated with the TPS. To check this, you could start the car and let it idle, and "massage" the length of the sub-harness, listening for hiccups or increases in RPM. Theoretically, you could even use a jumper wire to simulate "wot" and do the same thing, (AGAIN, listening for changes while "massaging") but I do not know how well the vehicle would handle a "wot" TPS signal when the throttle wasnt actually open past idle... Good luck. The hardest part is recognizing how truly simple this system is, and not reading more complexity into it than there is. Quote Link to comment Share on other sites More sharing options...
jmt Posted March 13, 2008 Author Share Posted March 13, 2008 ive checked the tps, ive cleaned it, ive ohmed it out, everything tested fine, ive adjusted it just to see if it was richening the circuit too early....no go on any of this. I dont think another tps would help since its just 2 sets of contacts. I feel that the problem might be somewhere else and maybe the tps is sending just enough fuel to make it choke, which makes me wonder if its possibly the afm screwing up since this is pretty much the only other thing that controls fuel mixture!? When I ohmed the afm my reading were about 40 ohms off on every reading...so could this be a problem? Hell I dont know at this point! Quote Link to comment Share on other sites More sharing options...
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