hard to start when cool - Page 2 - Nissan : Datsun ZCar forum :Nissan Z Forum: 240Z to 370Z
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post #11 of 23 (permalink) Old 08-07-2015, 11:52 PM
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the AAC which is on the right side of the engine is supposed to supply extra air for cool start you might check its operation. might also be that idle junk hanging off the plenum on the left side. I took it all off my 86 and never missed it. try feathering the throttle when you attempt to start and see if that cures the issue

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post #12 of 23 (permalink) Old 08-08-2015, 09:07 AM
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the AAC which is on the right side of the engine is supposed to supply extra air for cool start you might check its operation.
AAC is the idle control on turbo engines, an improvment on the the Idle-up solenoid used on NA engines (on the LHS of the plenum).
The Air Regulator is on the RHS of the plenum and supplies extra metered air when cold.

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post #13 of 23 (permalink) Old 08-09-2015, 09:55 PM Thread Starter
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Sorry, I wasn't precise before. The fuel pressure is 36 psi when I turn the key. So I think the FPR is good.

I'll check out the other suggestions.

My own theory is one or more injectors are clogged. Z Clinic in Austin is asking $120 to run a chemical/gas mixture directly into the rail to clean them out.
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post #14 of 23 (permalink) Old 08-11-2015, 02:21 AM
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My own theory is one or more injectors are clogged.
Clogged injectors would affect running in all conditions.

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Z Clinic in Austin is asking $120 to run a chemical/gas mixture directly into the rail to clean them out.
If it does not fix your problem, do you get your money back?

Next time your engine is stone cold, disconnect the MAF and see how it starts.

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post #15 of 23 (permalink) Old 08-11-2015, 12:14 PM Thread Starter
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If it does not fix your problem, do you get your money back?

Next time your engine is stone cold, disconnect the MAF and see how it starts.
I wouldn't think so, 'cause I just asked him about the fuel injector cleaning service, not to troubleshoot my issue.

I disconnected it this morning. 5 cranks and no start.
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post #16 of 23 (permalink) Old 08-23-2015, 10:50 AM Thread Starter
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Is it normal for the fuel pressure to drop to 0 after the car sits? I was thinking when I try to start it in the morning there might be air in the fuel line that takes a while to clear out. (?)
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post #17 of 23 (permalink) Old 08-24-2015, 05:07 AM
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Upon turning the key on and waiting for the prime to complete, I would expect the fuel pressure to get up to 37psi before the 5 seconds is up.

I would be inclined to re-check for CHTS code.

User awg might suggest a 87 NA ECU.
Right, swap in a 87na computer, Uses the same O2 sensor and has better fuel curves. Your 85 will start and run like an 87. No more lean surge on cold start.
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post #18 of 23 (permalink) Old 10-30-2015, 11:56 PM
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my fuel pump keeping going and does not shut off when it is cold - hmmmm! Did not do that on my 1982 280ZX - think my fuel pressure regulator is bad also!?


I can hear a hissing sound over the fuel pressure regulator - almost sounds like an air leak - but can not see any fuel leaking anywhere! Starts first time every time but runs rough and cuts out. disconnected vacuum line on FPR and applied vacuum at 25 PSI and sound of fuel pump changed but still did not shut off. Looking into ordering fuel pressure gauge. Think it is the FPR even though it does not leak fuel out the suction post when revved at 5000 rpm nor can I get any fuel out of it with portable vacuum pump and revving.

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Last edited by Nursx2; 11-01-2015 at 04:34 PM.
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post #19 of 23 (permalink) Old 11-02-2015, 04:38 PM
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Right, swap in a 87na computer, Uses the same O2 sensor and has better fuel curves. Your 85 will start and run like an 87. No more lean surge on cold start.
Hey, are the computers the same between auto and manual in the 87+, and would any 87-89 ECU swap in?
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post #20 of 23 (permalink) Old 11-08-2015, 10:06 AM
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Checked my fuel pressure from the tank and is was 39 PSI! Pressure goes up when rev engine which it is supposed to correct!? Still can not figure out why the pump stays on all the time with the key turned on and engine not running. Read in the Factory service manual this is supposed to shut off when engine not running as a safety feature. Is the fuel pump relay in the side of the passenger fender next to the battery?


Changed out the new CHTS sensor yesterday with another new one )more expensive brand) and no difference. Still runs better with it unplugged! Also changed out the connector with a brand new one!


Did seem to run better yesterday when it warmed up and also ran better when the A/C was on (under load) and I do not have the aux vacuum installed yet! Strange!

Last edited by Nursx2; 11-08-2015 at 10:09 AM.
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