Warm Start Stumble/Hiccup

[A1218]

Did a pressurized fuel cleaning on injectors. Didn’t help the issue where I drive and come back to the vehicle anywhere from 20 minutes to an hour and half on a hot restart where it stumble for a few seconds.

Sometimes it would even surge at a very low rpm for those few seconds. One time it even died when it did this. After that vehicle is perfectly fine. No drivability issues or problem with cold start and starting after few hours.

I know many have said could possibly be leaky fuel injectors but I want to make sure first before pulling everything apart. Did a fuel pressure test a while back and lost 10 psi in 25 minutes. Some say thats normal and some not.

Im including some data here
At idle around 850 rpms:
SHRTFT1: 9.4%
LONGFT1:9.4%
SHRTFT2:1.6%
LONGFT2:9.4%
ECT: 187F
MAP 4.8psi
SPARDKADV: 5 degree
When reving vehicle the short term fuel trims drop down to around 0 or even less sometimes.

Looks like those short term trims are high.Hopefully I get a code in the meantime I check around. But it’s been about a year now I’m dealing with this intermittent warm start stumbling and can’t find the cause of the problem.

Have taken the vehicle to a longtime Nissan tech I know. He checked it out and isn’t sure. Though I don’t believe he put too much effort into checking thoroughly. To begin with its hard to just replicate the issue since it’s in the time frame I spoke of. It did happen to occur when he was looking into it. I saw he try to adjust the IACV with engine on and I didn’t see any idle speed change though.

He did recommend the ECT sensor which was replaced and no change in issue. New distributor, leads, plugs, maf, air filter, fuel injection pressure clean.


Can someone help with the diagnosis

[mdmellott]

Bank 1 STFT is a bit on the high end but not too alarming. The 10 psi of decreased fuel pressure over 25 minutes is normal during that pressure test. Your timing, on the other hand, is not normal. Your ignition timing should be 13 to 17 degrees BTDC. 5 degrees is a problem.

[A1218]

Isn’t the distributor timing different from SPARKADV?

Because when I cold started it and checked with scanner it said 63.5 as opposed to that value I gave after driving for about an hour yesterday.

Thanks

[mdmellott]

Of course, the ignition timing will vary depending on engine speed, temperature, load, etc. The PCM has limited control over how much it can advance or retard the ignition spark event timing in ignition systems with distributors. The distributor adjustment sets the ignition timing within the limited range in which the PCM can properly control the spark event. With the engine warmed up and revving at an idle of 850rpm, the spark advance should be close to 15 degrees BTDC. When checking and adjusting the distributor with a timing light, the PCM control must be disabled first by disconnecting the TPS harness connector. Otherwise the mechanical set point where you clock the distributor, based on the timing mark on your crank pully as illuminated by the timing light, will be affected by the PCM and thereby throwing off a proper distributor adjustment. Distributor timing and sparkadv are independent adjustments yet totally dependent on one another for proper ignition timing function.

[mdmellott]

... the ignition timing will vary depending on engine speed, temperature, load, etc. ...

Proper timing belt tension is also a factor. If the belt is too slack and the belt tensioner can no longer be adjusted enough to bring the belt tension deflection between the camshaft sprockets to within the 13 to 15mm deflection specification while a 22lb force is applied to the belt between the sprockets, then the belt has been stretched past its limit and a new belt would be needed.

[VStar650CL]

Proper timing belt tension is also a factor. If the belt is too slack and the belt tensioner can no longer be adjusted enough to bring the belt tension deflection between the camshaft sprockets to within the 13 to 15mm deflection specification while a 22lb force is applied to the belt between the sprockets, then the belt has been stretched past its limit and a new belt would be needed.

God love you old-Pathfinder guys. The font of not-quite-obsolete R50 knowledge in this forum never ceases to amaze me.