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Hesitates in 2nd gear...

 
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hi91-318i



Joined: 08 Apr 2005
Posts: 114
Location: Hawaii

PostPosted: Thu Aug 18, 2016 10:19 pm    Post subject: Hesitates in 2nd gear... Reply with quote

91 318i M42

Been trying to figure out what is causing an occasional hesitation in 2nd gear (mostly). Idles fine, runs a bit rough while accelerating and down on power with lots of throttle.

It started when the CEL sometimes came on for a couple of seconds after a couple of miles after a cold start. Stomp test said 1222 which indicates running lean or rich. Eventually the 2nd gear hesitation started and later started feeling like down on power and runs a little rough while accelerating.

It does not feel like a cylinder is not firing but more like not enough fuel. Also a slight hesitation if I rev in neutral. Tailpipe is not black and plugs didn't say rich so thinking lean...

Changed the plugs, O2 sensor and can't find any vacuum leaks or cracked boots.

I noticed that the hesitation happens more often after idling for a bit like at a stop light. I read that the fuel pressure reg adjusts according to vac or load which got me thinking that the problem could be fuel delivery or rather lack of...got a fuel pressure gauge coming to check that out.

The more I think about it the more I think that the injectors are starving for fuel.

An old issue that I could not figure out also came to mind. The motor used to start right up in the morning with a very short duration of cranking but for the past couple of years it required longer cranking but if I cranked for a second, stopped and then cranked again it would fire right up on the second try almost like the first crank primed the motor.

I just read that the fuel line is supposed to hold pressure even after the motor is shut off. That got me thinking that perhaps it lost pressure overnight and the cranking built up the fuel pressure? And the idling at the stop light let the pressure drop so got hesitation?

Lots of discussion on hesitation but none are quite like my problem. Any ideas?
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hi91-318i



Joined: 08 Apr 2005
Posts: 114
Location: Hawaii

PostPosted: Mon Aug 22, 2016 2:22 pm    Post subject: Reply with quote

The check engine light has started to light up more regularly. It seems to come on at about 2 miles from a cold start and will stay on until I let up on the gas pedal and then not come back on but continues to hesitate and run rough at all throttle positions...but idles smoothly.

When I did searches for hesitation most stated that their hesitation occurred at 4-5k while I am having the hesitation at 1500-2000 rpm and mostly after upshifting to 2nd. Pressing the throttle more does not help and it runs rough.
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hi91-318i



Joined: 08 Apr 2005
Posts: 114
Location: Hawaii

PostPosted: Tue Aug 23, 2016 2:29 pm    Post subject: Reply with quote

I think I am going to check the throttle position sensor too...
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hi91-318i



Joined: 08 Apr 2005
Posts: 114
Location: Hawaii

PostPosted: Mon Aug 29, 2016 6:12 pm    Post subject: Reply with quote

The before the fuel pressure gauge arrived the hesitation went away. It's running a lot better but it feels like it's still not running 100% especially at 4k and up. Not really a miss but the RPM is just not climbing like it should.

I guess I still need to hook up the gauge and check the fuel pressure regulator and throttle position sensor.
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hi91-318i



Joined: 08 Apr 2005
Posts: 114
Location: Hawaii

PostPosted: Mon Mar 06, 2017 5:45 pm    Post subject: Reply with quote

I finally replaced the fuel pump this past weekend. I ordered the new pump several months back but it started to run perfectly before the pump arrived so never installed it.

Last week the CEL started to come on again and the hesitation returned so I checked the fuel pressure and it read 15#. With the pump relay jumped and return line pinched, no change to the pressure. Installed the new pump and reading now 50#!

Runs like a top since, starts easier and no hesitation.
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