Help: I have a sputter

#1

I am on my second DE day at VIR. The problem is that at the end of a thirty minute session the car starts to sputter esp. in at higher RPMs (5000 or so). It seems to happen mostly when I am going up the "S"s or down the hill after the back straight. It feels kind of like fuel starvation but I have a full tank. Maybe the mass air sensor is dirty? Could it be plugs? Thanks for your insight.

Jay

#2

Sounds like the fuel pump. If an '87, you have two - one in tank, one under drivers side door rocker panel. Later models only have one in the tank - passenger side back seat area - there is an access panel.
Ed

#3

I do have an 87. Do I just keep driving it tomorrow and fix next week?
We are on North course tomorrow.

#4

Look for a common thread. If it only happens in a certain place or under a certain kind of g load, consider that it might be a wire grounding against something. If that seems plausible, work to reproduce the symptom by wiggling wires.

I had this symptom at RA last year. Turned out to be a frayed CPS wire that was invisible until I pulled the SOB off.

#5

Agree with Ranger - could be a number of electrical gremlins. I’ve seen this with loose battery connections as well. Check everything. If it is the fuel pump, it will likely get progressively worse. I would drive it.
Ed

#6

edavidson wrote:

[quote] I would drive it.
[/quote]
+1

#7

Thanks guys
The E30 has been fantastic, by the way.
Nothing like getting a point by from a Viper GTS and a GT40!!

#8

I had a similar problem a few years back. Car would run great when you started it up cool. It would run longer the harder you drove. The fuel pressure regulator malfunctioned completely cutting off the return line. The pressure at the rail was about 100 psi so eventually the fuel pump would overheat and shut itself off. This was also in an 87is.

#9

There are 3 relays on the driver’s fender under the hood. Zip tie them down into their sockets. It’s my understanding they can vibrate loose. You also might want to try the diagnostic cap removal trick.

#10

I switched out the fuel pressure regulator and was the same.
-Starts to sputter and cut out at the end of a run.
-Seemed worse as day got hotter

  • Last run of the day could barely make it down the hill. Coasted in neutral and once I got to pit, did not sputter as much
  • It is like if it cools off, the fuel pump kicks back in.
  • Is it one of the two pumps going bad and overheating by the end?
  • Maybe just replace tank with updated tank and single pump?
    (fuel filter is pretty new, but could that be?)
#11

Like info above it could be one of many items. On my particular car I had a similar situation twice. First time was from a bad plug wire. If I would hit curbing it would cut out and it got worse on the straights as the car warmed. Second time was like Ranger and the Crank Position Sensor. Could not tell by looking at it but after an hour of diagnosing we found it and once removed it practically fell apart. IF the CPS is not sending a signal it shuts the fuel pump down. Can easily be mistaken for a bad pump.

The cars are old and anything that is original or looks original should eventually get replaced as it will fail at some point.

#12

If this is a regular occurance evrytime you get to 5K, you may have a bad MAS . Two cars including ours, with that problem at NJMSP this weekend. Thanks to Jon Allen and Pete Thibault for setting us straight and for this fix. The car acted like it was hit the rev limiter at 5K. We pryed the black cover off the top of the air flow sensor. There is a sweep arm that moves as the throttle is pressed. Pete had a voltmeter whic we set to manula mode, watching the meter it went open 3/4 throught the travel. the result you feel when driving is a sputter because there is interuption to signal for fuel so the supply is interupted.

You will see two grooves in the travel path of the arm, the dead spot is worn in one the tracks

there are two fixes -

  1. the simple one is the gently press down on the arw causing the two points to start move in a new track. if this works there will bew no more open circuit. We were luck this worked for us.
  2. the other solutions is remove the 3 screw that hold the plate under the arm and move the plate. We would have tried this if would could get the screw out…

Good Luck. This made a huge difference for Robert from Sat to Sunday but then we had other issues Sunday which you will soon learn.

#13

The distal part of the CPS wire does have some fraying/exposed wire.
Maybe this is it?
I am going to replace the CPS, fuel pressure reg, fuel filter, clean MAS and see what happens.

Where is the best place to get all this stuff <CPS, etc>?

#14

I was planning on cleaning and checking out the MAS at the track. It seemed like it might be the cause. I tried the pressure reg, first to no avail.

#15

I get all my parts form www.bimmerparts.com. Give them a call and Chris can help you out. Prices are good and he knows what you do with the car. Just tell him you race SE30.

Good luck.

#16

Replaced CPS and I think it might have fixed it. My next step is to replace the in tank fuel pump if this does not work.