Loss of power in my E30 Series car

[Driftit 1964]

Hey guys. I have a strange and hard to diagnose problem with my Series car.

My car is a PFL 4door 320. With a PFL M20B20.

Symptom: Under full throttle acceleration I can occasionally loose a ton of power intermittently. Occurs for roughly 2-5 seconds. This large loss usually occurs just after going through castrol onto the back straight going from 3rd to 4th and exiting the hair pin going from 2nd to 3rd. Once I have changed gear the car feels very flat. Is still accelerating but with my less HP. Enough of a loss that an evenly matched car will catch up to me easily. It has happened mid way down the back straight and coming over the hill.

This issue seems to get worse in the later laps. But the annoying thing is that it does not always happen.

This problem does not occur on the Dyno.

I run a near full tank of fuel for a race. 45L+

I have changed the plugs from stock to Bosch Super 4 to NGK colder temp plugs. With no change. Have changed the coil from stock to Bosch Super 40 to stock again with no change.

Will be changing the leads again soon.

Now after talking to Glenn I am going to check the fuel pressure while on the track when I can. But this power loss is not a miss and the car is not running lean. In fact it is running quite rich. When this car does get fuel surge she stutters quite badly.

Could it be something to do with the TPS? Would it cause a problem like this?

Edited September 13, 2009 by driftit

[OLLIE 26]

fuel related ...

first thing you should do - remove the fuel pump relay and wire in a dedicated on/off switch on the dash for the fuel pump. I have had so many problems with these relays! i could almost guarantee that's what it will be.

[tibbs.james 1]

Does the E30 ECU vary fuel pump voltage depending on engine load/ throttle position ?

I have had this problem with a Nissan ECU / fuel pump circuit and Ollies method cured my problem

[QuickSilver 0]

I've had a VERY similar problem on my old P/FL m20b20.

In the end I went through exactly the same stages as you have done, plugs, leads, coil, replaced fuel relays, fuel pressure regulator etc. In the end my problem was the air flow meter going haywire.

I can't tell you what exactly it was doing to make it nuts, but it seemed like it would stick (even with a big clean) and suddenly through higher rpm I would get complete flat spots, loss of power (still accelerating but at a much slower rate) and they would be intermittent and only under load.

I assumed because the AFM was faulty it was sending irregular/incorrect signals to the ECU therefore fueling incorrectly.

Swapped it out and the problem was gone.

Hope this is of some help, one of many possibilities of course.

Edited September 14, 2009 by QuickSilver

[Gus 5]

Agree with the above, an AFM or fuel pressure issue. I had a fuel pump die in the same spot you are talking about too. Good luck

[|ncary 0]

I assumed because the AFM was faulty it was sending irregular/incorrect signals to the ECU therefore fueling incorrectly.

Swapped it out and the problem was gone.

Almost all of the time a AFM goes bad, the contacts are worn out on the inside. What you can do is crack the top cover and bend the 2 contact arms down so they are on a different track and have more pressure on the board.

I've done it to both of my E30's and there is a noticable difference in fuel use and maybe some torque haha.

[RyanG 0]

Ive had a similar problem with a fuel pump that was on its way out.

[Driftit 1964]

Cheers for the tips guys.

I think I will set the car up with a seperate fuel switch and new pump. And then try a few different AFM's. Hard to find a good 24 year old AFM.

Then get her back on the Dyno and test it at a Puke open day.