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Hey there, 75 280z here. Stock original engine with fuel injection. Geting really low and rough idle when car first started. It almost doesn’t run until I pull the vacuum hose off the FPR, then it idles much better and warms up quicker. And yesterday I drove it like that with the FPR disconnected and is much faster and smoother. What could be wrong here? I’ve checked all my readings per the ‘fuel injection bible’ and they are all accurate. Also when I unplug the cold start there is no change at early startup. Any tips for items to check would be most helpful thanks.
 

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Hey there, 75 280z here. Stock original engine with fuel injection. Geting really low and rough idle when car first started. It almost doesn’t run until I pull the vacuum hose off the FPR, then it idles much better and warms up quicker. And yesterday I drove it like that with the FPR disconnected and is much faster and smoother. What could be wrong here? I’ve checked all my readings per the ‘fuel injection bible’ and they are all accurate. Also when I unplug the cold start there is no change at early startup. Any tips for items to check would be most helpful thanks.
If it runs better with a vacuum leak (leaving the vacuum hose to the fpr unplugged) that means 2 things (this was my issue that the PO did). #1 you have vacuum leaks to take care of and fairly large ones at that. #2 in order to compensate for that, the PO must have REALLY cranked your idle control screw to even get the car to run to compensate for the huge vacuum leak.

The easiest way to find vacuum leaks is to smoke the engine (don't do the method where you spray starter fluid on your engine unless you want to start a fire). Follow the method outlined in this video (except use a hand-pump from Harbor Freight (~ $7) and a pack of cigarettes to fill the engine with smoke to find the leaks which is much faster and easier to do.
 

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check fuel pressure see if FPR is working right. IF something is causing a lean run, perhaps disconnecting the FPR vacuum hose (there by increasing pressure at idle) may be compensating for lean ECU by adding fuel from increased pressure. Check water temp sensor at pin 13 and ground of 36 pin ECU connector. See if resistance in spec for temps per FSM.
 

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Discussion Starter #4
check fuel pressure see if FPR is working right. IF something is causing a lean run, perhaps disconnecting the FPR vacuum hose (there by increasing pressure at idle) may be compensating for lean ECU by adding fuel from increased pressure. Check water temp sensor at pin 13 and ground of 36 pin ECU connector. See if resistance in spec for temps per FSM.
Hi Dave, I have distracted for awhile off the Z now. Getting back to this problem. Thanks for your reply! I checked this yesterday using the 'fuel injecton bible' for the 280Z and everything in spec except the AFM readings are off... Could that be causing this poor and long warm up? Also, could it be the Thermotime switch and cold start valve not working?
 

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Discussion Starter #5
Vacuum Leak found!

Big vacuum leak at the throttle idle adjustment screw! Anyone have any ideas on how to seal that???
 

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Big vacuum leak at the throttle idle adjustment screw! Anyone have any ideas on how to seal that???
Unless you somehow find the seals to rebuild it, you can't properly fix it (outside of buying a new one).

Here's and unpopular suggestion tho - if your idle is set, seal it with a bunch of black silicon glue. LET IT DRY FOR A WHILE - you don't want glue being sucked into your engine and you'll be set.
 
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