strange issue with 78 280z running - I'm at the end of my rope!

[Wwildman]

When I got my car it was sitting for 14 years and the AFM had clear silicone around the cover . I opened it and found that a butter fingers mechanic unwound the spring. I reset the spring and replaced the coolant temp sensor, all injector connectors with injectors,and new FPr and pump. Car stalled and would not start. I had no spark or injector pulse. I put a new Ignition transistor under the dash and a new pick up coil in the distributor. Also I cleaned all the grounds and added two more grounds

[Zed Head]

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.

It's not how long the engine has run, but how much current is running through the module that heats it up. High RPM passes more current through the sensitive parts as it generates more sparks. High RPM, heat, weird behavior, turn off engine, cool down, back to normal.

[hr369]

bucking during decleration is probably tps adjustment.

did you take the cover off and inspect the contacts?

http://www.atlanticz.ca/zclub/techtips/tps/index.html

[gheiser70]

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

Edited May 18, 2014 by gheiser70

[240260280z]

Thanks for the update:

Temp sensor checks out at the sensor. I assume the wiring from the sensor to the ECU is OK?

Are the injectors green? The full part number should be A46-000001 for stockers.

Getting a full set of injectors would give piece of mind however you can easily pick up a few used ones and flow all and clean some to get a relatively matched set.

Edited May 19, 2014 by Blue

[Zed Head]

If I had a stock system and was looking to buy new injectors, I would get Standard brand, either the FJ3 or FJ707T. (Rockauto has good deals. Data is sparse but they might be better for heat soak than others.

Before you buy though, since you're going to take things apart, you might leave the injectors connected to the rail when you remove them (they'll come out as an assembly), reconnect or leave connected the fuel hose and electrical and squirt in to some containers for a short time ( use small coke bottles). You'll get an idea of how unbalanced the injectors are. Do it outside though, with a breeze and no open flames.

You should notice if #5 is totally dead. The engine will run a little rough and the spark plug would be dry or oily, but different from the others.

[gheiser70]

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.

[240260280z]

Good stuff. You know what you are doing...keep at it and you should have it in good running order soon.

[FastWoman]

A single MIA injector isn't going to cause your engine to cut out completely above 3kRPM. It will give your exhaust a chugging sound, and you will lose 1/6 of your power throughout the power band. But no, it won't cause your engine to drop out.

A non-working injector also will not affect the fuel/air ratio balance. The cylinders that are running will be getting the same mix as they would if the #5 injector were working.

Your injectors could just be gummed up with varnish. If there's any flow at all through your #5, there's hope for cleaning it up. (A stuck injector might free up once it gets hot. Does it show a normal resistance across its contacts?) I once cleaned up a gummy intake by running some Chemtool B12 through it. It took a bit of persistence, but it finally paid off.

Have you taken the cover off of the TPS to see if anything is amiss? Have you confirmed the correct signals at the big ECU connector when you move the accelerator pedal?

[madkaw]

As Zed said-it's the amount of current that might make an ignition issue, not so much the heat. The coil might be caving under high load situations and thus cutting out the ignition. I agree with Sarah that one injector is not your issue.

Keep up the good work, most guys with only 5 posts are still wondering what the PCV does-

[gheiser70]

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.

Edited May 19, 2014 by gheiser70

[Zed Head]

I've never really understood why water in the TPS would cause the problem that it does but I think I have it figured out now, thanks to this thread. I attached the relevant passage from the FSM. Water in the TPS apparently makes the ECU think the throttle is closed. Details in attachment.

One way to get a better idea of if it's the TPS is to watch the tachometer and note the RPM, when the cut out happens, and when it bucks. The tachometers aren't known to be super accurate so you may not see exactly 2800 and 3200 RPM, but if it happens consistently around those numbers, that would be a good indicator.

If that's not it, then the old fuel pressure gauge poking out of the hood plan would let you know that you're maintaining fuel pressure. If you have proper pressure but it still cuts out, then electrical has more potential.

Edited May 19, 2014 by Zed Head