NismoPick

Did you ever do this? It sounds like you are just throwing new parts at it without doing any testing first...

If you have a broken or corroded wire somewhere, you can replace every sensor 10 times, and it won't make any difference.

mrprotoplasm

alrighty then, thatll be my next to do, must have missed that advice. yeah, throwing new parts at it blindly has admittedly pretty much been my strategy. Although upon replacement, they usually seemed to be wise replacements.

mrprotoplasm

Thanks for the last bit of advice there, while checking each connection I noticed something on the intake end of the Auxiliary Air Intake, which turned out to be a hidden damage to the rubber hose and it was allowing for extra air to be sucked in to the engine, thus explaining why it only happened when cool. I hope this symptom creates a record for anyone who experiences this unusual situation of crazy revving engine when cool, but it still doesn't explain my original problem (which I have not had enough time to determine if it exists or not yet) of the engine sitting for 30 minutes or so and then struggling upon start up, so we'll see if this fixed everything. Amazing how such a small imperfection can cause so much chaos.

mrprotoplasm

Scratch that, it didn't fix it, it boggles my mind that this problem goes away sometimes (but 9 out of ten times, it persists). Maybe one day, if I ever figure this out, I'll post what the problem actually was. Until then, well, it just sucks. At least it runs great once warmed up.

SHADY280

check to make sure things like the egr is functioning or not when its supposed to. maybe its stuck partway with a piece of carbon in it. also the cold start valve can be checked with battery voltage and a ohm meter. make sure the bi metalic spring is returning in the aux air valve. these all are what control cold running. that and really really check the harness for all the temp sensors. they tell the computer when the engine is at operating temp. follow the fsm for that one. you use boiling water to do the test with an ohm meter. the sensor could be telling the car its cold far longer than it should. its baseline could be telling the car its at 5 deg to start instead if ambient temp. then when it warms up it finally is closer to where it should be. just some things to play with for ya. its all about the testing.

mrprotoplasm

I just pulled the harness and tested every sensor in the car today, everything was within limits according to FSM, I haven't boiled any temperature sensors to see if they are faulty at higher range, but at room temperature they were good, I'll look into that next. I also checked the EGR valve, it seems okay, I replaced it not too long ago.

The cold start valve is only supposed to inject fuel when it is cold outside (I used to think that "cold" was a relative term to the normal operating temp of 180, so anything less than that would be "cold") below 57 degrees, if I am reading the manual right, and then it only stays on long enough to get the engine running, like just a few seconds, correct? I'm just trying to eliminate it as a possibility

I also manually checked the auxillary air valve and the engine struggles when I choked the rubber hose while cold and no change once warmed.

Thanks

ThaPimpShrimp

If I understand how the csv works correctly (I have a turbo car, so no csv) I'd just unplug the connector when your car is warmed up and then try driving it to see if it'll stall. If still yes, it's also possible the csv is just leaking fuel.

My engine used to die sometimes when I pushed in the clutch going downhill because it was running to rich and the engine flooded. So it's a possibility.

NismoPick

That actually doesn't make sense. Unplugging it and still having the problem doesn't eliminate or narrow down the problem. Usually the CSV gets clogged with carbon buildup and doesn't spray [enough], causing cold start problems. A leaking CSV will create a pool of gasoline at the bottom of the intake plenum, I doubt that would be the cause of hard starting.

Going back to the basics... for no start or hard start, check:
-spark at all 6 cylinders
-fuel pressure

ThaPimpShrimp

Hmm you're right, doesn't make a whole lot of sense.. I more meant that if it stopped then that caused it, but I guess you could just test the thermotime switch which I believe opens the csv.

Perhaps if there is a pool of gas in his plenum then when he travels downhill it runs into the engine and floods it! Who knows haha

mrprotoplasm

Any chance my issues stem from a bad ECU? I mean it's quite strange, no problems when running after warmed up, runs like a dream, it occasionally runs okay when cold, but usually the tach starts going crazy and the engine coughs a bunch when I try to accelerate (it goes, but slowly). Sometimes it starts acting up after about 10 seconds of being on and sometimes 3 or 4 minutes, it is not consistent, and it is driving me mad. I tested the grounds on the ECU and they checked out ok on the multimeter.

Winter is coming and it will take twice as long to warm up, not looking forward to that.

ThaPimpShrimp

Sorry...

I'm not very helpful right now.

mrprotoplasm

Nice... and accurate.

85zxt

Don't unless this person has dealt with this issue on a Z and resolved it. Unlikely! My car has paid people a couple thou at least to resolve this. Not! We know it is heat related but what? I just noticed i don't have my heat shields on the turbo side and need to replace those and see if that resolves my start - idle up - die - rough restart and die issue. My car has been sitting for years waiting for "the fix". Z31T here. - Good luck - I have replaced all of the above items and then some. Not the solution - trust me. ml

mrprotoplasm

Thanks for the advice, I am of the same school of thought, I was guessing a dealer would be my best bet, but they will unlikely not know. I think the heat shield might be our common denominator, I have aftermarket headers on mine (NA) so I will grab some heat wraps and see if that helps. I can't stand paying other people to look at my car, only because I have never found an honest person who wants to do anything but rip me off. On that note, I am in Central NJ, anyone round here know an honest place?

NismoPick

In case you missed this...

Check for spark, check for fuel (none or too much)...

I advise against header wrap. It quickly shortens the life of the header (Google it). If you want to see if engine bay heat is the culprit, remove your hood and take it on a drive that would normally produce the problem.

Don't over complicate this.

mrprotoplasm

I have seen some stuff on header wraps not being good for headers, but it seems to me it is an issue of moisture, not really heat. The problem is if moisture forms or gets in between the header and the wrap, then there is an issue. This happens if installed incorrectly, or I suppose, if moistened directly. I think it might depend on the material the wrap is made from, but that is conjecture.

However, I will say that since I have run a diagnostic from the harness, the issues has stopped, but its too soon to celebrate. It might have something to do with cranking up the idle, I pushed it to 900. If this resolves the problem, what are the negative side effects of my solution?

ThaPimpShrimp

I just realized I completely mixed up two threads which is probably why my posts didn't make much sense. Oops.



Well, before worrying about that, just dial your idle back down and see what happens.

mrprotoplasm

Idle drawn down to 800, no difference, problem is still intermittent, I'm going to try a new ECU.

(Oh, spark and fuel good)

jalexquijano

I also have an unsolved overheating problem which causes rough idle and stalling on my 1972 240z with round top SU carburetors, which i describe as follows:

Crank the engine at the garage, if it does not crank immediately i need to pull the choke for at least 1 minute. After that i push it back. Temperature needle is at 0, drive the car from the parkway until i head myself to the streets. At the streets, i can drive around nice until i get to a couple of traffic jams, lights and after 15 mins of driving temperature reaches to a Little less than 3/4 in the temp gauge. Idle becomes rough lowering from 1000 RPM to 500 or to 400 sometimes and rises back. Eventually car stalls and i have to crank it again.
Its a real uncomfortable situation as i only remain with the possibility of driving the car on sundays when there are few cars and no traffic jams. I bought this car 2 years ago and have already replaced the following parts:
1. Pertronix ignitor 1761 and Pertronix Coil 40511 (3 ohms) bypassing the resistor.
2. Far 311 Race cam was replaced with Schneider 274F camshaft, with springs, lashpads and rocker arms. The car has a New Datsun L24 motor with crank and rods from a L26, special oversized 84mm flat top black coated pistons from D.L. Potter Engineering with E88 Head (This was done by Datsun LLC to the Previous Owner).
3. Water pump
4. Fully refurbished SU Carburetors by Ztherapy (US$650.00)
5. Fan clutch
6. 170 degree Farenheit Thermostat.
7. Airtex 8012S electric fuel pump (4psi)
8. New NGK Blue Spark Plug Cables.
9. NGK BP6ES Spark Plug.
10. MSA Fiberglass Fan Shroud


I guess the former owner knew about this issue and decided to sell the car. With all the money i have spent including labour i could have bought 3 new engines. Unfortunately, mechanics here in Panama have few or scarce knowledge on this vehicle and hence i am looking forward to hire a US Datsun experienced mechanic that can assist me on setting up this car properly. Anyone willing to help?