gheiser70

Hi - The 78 280z has been running well most of the time since my last go round with the salt bridge on the TPS and new injectors. However I (and my son) have had intermittent stalling issues when on the road. Both times in the last month, we were able to "rap" on the ECU box with our knuckles and get the car to restart for the ride home. Once it happened after about 10 miles away from home, and once less than a mile. Both from cold starts. We have reflowed the pins from the 35 pin connector to the ECU board, but this seems to be a vibration issue. Some times I can change the way the car runs in the drive way by "rapping" the ECU. Unless I can find something obvious, I'm considering a rebuilt ECU. Has anyone out there used one and how did it work. Cardone sells one through the general auto parts stores and MSA and z car source offer rebuilds as well for more money. Any thoughts? Thanks, Greg

So - More good news. 20 min road test with multiple WOT runs (I may have exceeded the speed limit -) NO cutting out was observed, just smooth acceleration. So, it appears the salt bridge theory was the answer. Thanks to Fastwoman, and all others on the board that helped me through this troubleshooting adventure. I'll keep you guys updated if anything changes, but right now I'm going to enjoy the sweet sound of the inline six humming along! Thanks again to all. Greg

Fastwoman, I think your salt bridge insight may have been the answer. Yesterday I scrubbed the TPS with a thoothbrush and good old soap and water, plus some white vinegar for good measure. The rinsed everything in distilled water. I also did the same for the TPS connector in the engine bay. I then dried the components with compressed air. Drive way testing shows no cutout when revving to WOT. I haven't had a chance to road test, but I may today. As for the other question, the cut out does (did) take place whether or not the engine is under load, ie, the engine would cut in the drive way at WOT as well as on the road. Now I just need to get out on the road, get her good and warm and see what happens.

Captain O - I don't get a misfire at WOT, the engine stops running like a switch was flipped. Tach remains stable however. Fast - I'll try to clean the TPS as you suggested. I've taken the ECU apart and checked for solder bridging per your recommendation. Checked with the Multi meter where the pins hit the board and the pins themselves. No continuity between 2&3. I was checking at 2000K ohm range (for the TPS switch checks), still showed open. The inside of the TPS looks visually OK. I agree with you that the chance of contact jumping is small. I'll try to get some measurements but the idle contacts are well apart in WOT mode. I'll also double check the wiring. Greg

Zed, I'm using a middle of the road multimeter to do my checks. It's no Fluke, but no harbor freight either. It shows infinite resistance. Dan's post above (# 25) shows a similar result with the TPS disconnected. I surmise that the disconnecting the TPS removes any signal from entering the ECU's fuel cut circuit. I'd love to get a schematic for the ECU, so I could see how the signal is processed.

Zed, I guess I'm not saying it correctly. Pin 2 shows continuity at idle. Then, when the throttle is depressed, it is open (no contiguity) all the way through the rest of the stroke of the throttle, including wide open. At all positions other than WOT pin 3 shows No continuity. At WOT pin 3 shows continuity. This is correct per the FSM. Blue, I also thought the wires might have been reversed, but they are correct at the 35 pin connector, so I don't think that is the case.

Weekend update: So new injectors from rock auto were installed with new O-rings. Slight miss at idle is now gone. Screw driver to ear test confirms all injectors "clicking" now. TPS saga: Zed - I reconfirmed that pin 2 at 35 pin shows continuity at idle and open when accelerator is depressed all the way to full throttle. Also, pin 3 is open at idle and all the way until the last couple of degrees till full throttle is reached then it shows continuity. I cleaned the contacts with 1500 grit sandpaper and spray contact cleaner and repeated the above tests. They are the same at the TSP and 35 pin connector. The fuel cut seems to be consistent at about 3K rpm, only when at full throttle - ie. it will rev past 3K and accelerate well unless the TPS sends the full throttle signal. As soon as I release the throttle, normal running resumes. As a further test, I disconnected the TPS wiring from the TPS, and there is no cut out in this mode of operation - ie. I can run at WOT with no cut out of the engine. I think these tests isolate the issue to the ECU. It seems to be sending the fuel cut signal under WOT operation. I was wondering if anyone has a schematic for the ECU. My son and I were trying to trace the circuitry for the TPS, but it seems nearly impossible without a diagram. There is also a test in the FSM (section 8.3) for throttle valve insulation. The reading between all three pins on the TSP and body ground should be open. My TPS passes this test as well. Has any one purchased a rebuilt ECU from MSA? And if so, how was it? If I can't find the schematic for the ECU that may be my next step.

Fastwoman - I did have the TSP apart and all looked well. My son and I check for continuity at idle and at full throttle at the 35 pin connector. I don't remember the exact pins, but the continuity checked OK at both positions. Thanks for the encouragement. I have quite a bit of experience with air cooled VW's and old Mopars, but alas, they were all carbureted. Those are fairly forgiving systems, fuel, spark and compression and they generally run well. I'm learning a lot about 40 year old electronics though. The trickiest part of electronics I've dealt with on the old cars was the old "ballast resistor" in the early Chrysler electronic ignitions, and for that you just kept a spare one in the glove box if it crapped out! I do have a spare 12 volt coil, when I get the injectors sorted, I'll swap it out and report back.

Thanks, Blue the temp sensor was checked at the ECU (35 pin). The injectors are green. Zed, My son and I had the fuel rail off this winter to replace the plastic holders and O rings on the injectors as I think 5 were broken (the holders). We cranked the engine and all the injectors were firing then. (we didn't measure flow, just confirmed they were all spraying). Spark plug looks much whiter than others after running yesterday. I believe the injector failed during the time I replaced the leaking brake booster and M/C. This is what increased my frustration. I assumed fixing the leaky booster would make a big improvement in how the car ran. When the new issue with cutting out cropped up I went a little bonkers and got away from basic troubleshooting. I'll update again after the injectors are replaced.

Blue, The best I can tell the injector PN is A46-00 but its awful hard to see. Zed Head -Tach needle remains steady during the "episodes". So, here is my update. Replaced plugs with new, removed pot and reconnected temp sensor as stock. Temp sensor OHM = 2730 at 70 degrees this AM in the garage, the car sat all night. Rechecked vacuum = 18in at idle. Rechecked Fuel pressure. Looks like 28 PSI at idle. Checked TPS - function was OK. Idle running much better and smoother with pot removed. Went up and down the road and still cut out between 3 - 4K RPM when accelerating hard. I was also able to peek at the under hood FP gauge and I didn't see any pressure drop during the episodes. So, back to the garage and I did the old screw driver to ear check on the injectors. Found a problem - injector #5 - No click at all. Swapped injector wires from cylinder 5 and 6 and injector 5 still fails to click. Injector 6 acts normal no matter which wire (5 or 6) is attached. So I believe the problem lies with the injector, not the wiring. I figure running on only 5 cylinders is not good for hard acceleration!!! So what do you guys recommend - one new injector or a new set of 6? Digging through the PO's paperwork the injectors were replaced in 1998 and about 3,000 miles ago. Any recommendations on sources? From what I see on the internet, prices vary quite a bit. Anyway, new a injector or injectors are in order before any more tuning takes place. On second thought, I'll probably buy 6. If one went south, who knows when the next one will fail. Thanks for the advice so far. Greg

Thanks again. I'll recheck the TPS, because it does seem that the fuel (or spark??) is completely cut when the car acts up. I have considered the ignition problem as well (module failure or coil) when the car has run for a while. At this point the problem is not related to how long the car runs. Anyway I have my niece's baptism today, but I'll try to get to the garage this evening. I'll remove the pot as well and try again with clean plugs. I'll also check injector P/N. I don't think the AFM was open It was replaced < 1000 miles before the car was parked. The AFM P/N is A31 625 000 - Is that correct for 1978? It looks like there is clear sealant around the black cover.

Thanks for the replies. I'm using NGK plugs, but I probably need a new set. No water has gotten into the TPS and it checks out. I did replace the PVC valve. I don't get any black smoke from the tail pipe. My in line FP gauge is just after the filter and was cheap from jegs so it may be off a little bit. The reason I wanted to try the pot was for the cutting out problem. Many posters (from my searches) seem to think this is caused by a lean condition. I have good hot spark, but if my plugs were slightly fouled from before I changed the brake booster, I suppose they could be failing to fire under a hard load when accelerating. The Pot did seem to reduce the cutting out under load, but the idle went to crap. It was a 5 dollar attempt and no harm was done, as I just wired in in the engine compartment, without cutting the harness. I'll get a new set of plugs and try from there. It has a new air filter, but I'll take a look for varmints. I had the AAR off and I seemed to work well. The fast idle works when the car is started and settles down as it warms up.

Hi, I've got an frustrating issue with my 78 280z. I bought it last fall from the original owner ( a very nice lady). It had been parked in her barn since the early 1990's. She said she was afraid it would leave her stranded. Any way, she had a lot of work done to it before it was parked, new AFM, fuel pump, injectors ect. I dropped the fuel tank, cleaned every connector, put new plugs, wires, tune -up parts, cleaned the 35 pin connector and reflowed the solder connections in the ECU, fuel filter and pressure gauge. I'm getting 40 PSI with the FPR disconnected and 32 or so with vacuum to it. I don't believe I have any vacuum leaks. I was pulling between 17-18 in. Vacuum. All FI components spec out per FI bible. Valve adjust also done. Timing set at 10 BTDC. After all that I was still fouling plugs with what seemed to be a rich condition. I then found that my master cylinder was leaking into the brake booster (it was full of brake fluid). I thought I might have been burning some brake fluid causing my "rich" condition. So, I replaced the booster and M/C, then I found a new issue. When running down the road, the car would cut out under hard acceleration, like some one flipped a switch, when I back off the gas it kicks back in and bucks like a bronco. After reading information here and the Atlantic z site I installed a 5K pot in line with the water temp sensor. It helped some but I still need to adjust for the best condition. Now though, my idle has become unstable and I'm only pulling about 15 in vacuum. The real brain teaser is that when I pull off the vacuum line for the air con. control to hook up my vacuum gauge, the idle increases and smooths out. So the car idles better with a vacuum leak - what gives??? Any input would be welcomed. Sorry the post is long, I just wanted to give some background.