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Power loss at high throttle input

voetganger

New member
Joined
Mar 30, 2020
Hi all,

I am in the process of finishing my PRV to b230fb swap. Running into a problem however: The engine starts up fine and idles relatively smooth, especially when warm. However, when I quickly press the throttle, it hesitates a bit before revving up. When driving it, it accelerates fine when I give it 0-60% of throttle. Above 60%, the engine starts making a different noise, a bit hollow I would say, and loses power. It also backfires through the intake sometimes. I suspect the valve timing is wrong, so I will look into that. I am looking for other problems that might cause this behavior.

The car is running buchka's wasted spark ignition, with fresh plugs/wires and all. That is the only modification I did to the engine, everything else is stock.

I am a bit less sure about the injectors, they might be less than optimal. Could partially clogged injectors also cause this?

Also the ECU is not getting its vss signal, however from what I've read this should only lead to a wonky idle sometimes and running rich when decelerating. I will connect it up someday.

Thanks in advance!
 
It helps when you mention what car model, year and fuel system. I suppose it's LH 2.4, correct?
The way you describe the symptoms makes me think the pressure in the fuel rail is too low. Should be about 5bar unregulated and 3bar regulated.
The harder the engine is commanded to work the more open the throttle is the lower the vacume in the intake the more fuel pressure the FPR should provide
- the fuel pressure regulator could be faulty. Try clamping the return line shut. That should raise the pressure in the fuel rail to about 5bar.
That should really be enough to run a B230FB (130hp)
- check if the in-tank lift pump is working
- check if the high pressure fuel pump is flowing enough fuel. You should see a powerful stream of fuel
- check the fuel filter, it's often neglected and could be clogged up
- check if the fuel tank venting is working (no venting will result in the pump gradually sucking a vacume in the tank, if this is the case you should hear a whoooshing sound (= air rushing back in) when you take the tank lid off.)
 
@janspeed:
It's a 264te from 1980. Engine is from a 1991 940 I believe. It is indeed lh2.4.

Thanks for the suggestions, I will try and see what happens when I clamp the return. And check both pumps.

@harlard it is a n/a engine. Intake hose seems to be fine.

I found a video of the engine doing what I described. I think that would help with diagnosing it, so I uploaded it here: https://youtube.com/shorts/JzlZBTDEh4Q?feature=share
Note that the AMM is not installed, I did not want to damage it with the backfiring. However, it does not make a difference with the backfiring, only idles a bit rough and runs quite rich without it.
 
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