Slight hestitaiton while accelerating.

paronoff · Post by **paronoff** » Sun Jan 25, 2009 9:09 pm

1980 528i auto feels like it is fighting a slight head wind when accelerating above 65 mph. Engine does not mis-fire and still accelerates well, it just feels like it is being hit with a slight head wind. Changed the O2 today because light was flickering but no change in this problem. Any ideas would be appreciated.

1st 5er · Post by **1st 5er** » Mon Jan 26, 2009 10:43 am

Sorry I can't help, but am interested in your diagnosis and resolution.

Chris Itterly · Post by **Chris Itterly** » Thu Jan 29, 2009 9:22 pm

Start with the timing, then check the fuel pressure.

Ignition Timing:
Check the Haynes manual, but I think it's 25 degrees BTDC. There is a ball on the flywheel you time to. Remove the vacuum lines from the distributor and plug everything. Set the engine at 2200 RPM and get the ball in the window on the bell housing. Tighten the distributor, reconnect the lines. Done.

Ignition timing can make a big difference, sound like there's not enough advance. My automatic car pulls all the way through to 125 mph, around 5000rpm in "D".

Fuel pressure:
Add an inline gauge from summit racing, I would be concerned with anything less than 45 lbs, but that pump should be up around 80 lbs.

Good luck

paronoff · Post by **paronoff** » Thu Jan 29, 2009 11:33 pm

Borrowed a timing light and dwell/tach from a co-worker. I plan on changing plugs, air filter and do the timing this weekend. The timing specs for my car is 22 deg. BTDC @ 2200rpm. I've read the FAQ and ready to go. I will post results.

paronoff · Post by **paronoff** » Sun Feb 01, 2009 10:39 pm

I tried timing the car today. There was no change in advance or retard as the vacuum hose was removed or replaced on the distributor. Something is not right. So it is off to the mechanic for a vacuum test or distributor rebuild. I will also have them check fuel pressure.

YouTube · Post by **Peter Florance** » Mon Feb 02, 2009 5:54 am

paronoff wrote:I tried timing the car today. There was no change in advance or retard as the vacuum hose was removed or replaced on the distributor. Something is not right. So it is off to the mechanic for a vacuum test or distributor rebuild. I will also have them check fuel pressure.

Did you check to see if there was vacuum on the hose. The advance side goes to ported vaccum and there should not be vacuum at idle.

Mostly they get sticky and a little spray oil seems to free them up. Don't forget to oil the felt pad under the rotor (where centrifugal advance can stick; which could be your issue)

paronoff · Post by **paronoff** » Tue Feb 03, 2009 11:23 pm

Mechanic checked out timing (spec), vacuum (no leaks), distributor (okay). Fuel pressure was not okay. 30 psi which is below spec. Fuel pump is suspect, hum is not constant. It goes up and down in pitch slightly, not with the gas pedal just at idle. Looking up FAQ to see if change out is DIY. There are supposed to be 2 fuel pumps for this car. In tank and outside the tank. Any suggestions on how to test them?

YouTube · Post by **Peter Florance** » Wed Feb 04, 2009 6:21 am

paronoff wrote:Mechanic checked out timing (spec), vacuum (no leaks), distributor (okay). Fuel pressure was not okay. 30 psi which is below spec. Fuel pump is suspect, hum is not constant. It goes up and down in pitch slightly, not with the gas pedal just at idle. Looking up FAQ to see if change out is DIY. There are supposed to be 2 fuel pumps for this car. In tank and outside the tank. Any suggestions on how to test them?

If a full tank makes it run better, in-tank pump is suspect.

30 psi with vacuum hose connected is pretty close. What is the pressure with the regulator vacuum hose disconnected? Should be 36-38 psi

paronoff · Post by **paronoff** » Thu Feb 05, 2009 12:19 am

No change. It stayed at 30.

YouTube · Post by **Peter Florance** » Thu Feb 05, 2009 8:08 am

paronoff wrote:No change. It stayed at 30.

That seems low
Full tank?

paronoff · Post by **paronoff** » Thu Feb 05, 2009 11:55 am

No. 3/4 of a tank. Passed smog though.

YouTube · Post by **Peter Florance** » Thu Feb 05, 2009 12:08 pm

I agree that the regulator is probably stuck open relieving too much pressure.

Pump could be weak, but I think the pressure would be moving around a lot if pump was weak

Pierre · Post by **Pierre** » Sat Feb 07, 2009 12:31 pm

An old clogged muffler would also cause similar symptoms.
And check your fuel filter before replacing the pumps. A clogged filter will also cause a loss of fuel pressure.

paronoff · Post by **paronoff** » Sat Feb 07, 2009 9:05 pm

Muffler is new. Filter has less than 10,000 miles on it but it certainly would be a good place to start.

Firstfives.org

Slight hestitaiton while accelerating.

Slight hestitaiton while accelerating.

Will try timing this weekend.

No luck timing

Re: No luck timing

Too much exhaust back pressure