928 s4 car running heavy

[Big Load]

hi guys
when i accelerate my car feels heavy not impulsive. heavy is the only way i can describe it. or the response on pressing the throttle is delayed by a few seconds. does that make sense?? almost as though she is choked!!and needs more gas to move. could something be blocked? I haven't got around to changing the fuel lines yet or changing the vacuum lines. could that be the cause?

gearbox seems OK, no knocking, high revs or issues i can see or tell.

Then when i do move i hear what i can only describe as a flapping sound not a smooth acceleration sound. if i take my foot off the accelerator the sound goes away. maybe exhaust?? but it doesn't sound blown

help

[Big Load]

owww yahh, buy the way can anyone recommend a good vacuum test equipment?? is there a check I can do to see if my exhaust/ cats are good??

[Big Load]

I found a better way to describe my problem ...lack of power on throttle .....and flapping sound when running

helppppppppppp

[harborman]

Can you be a bit more descriptive. Is the "flapping noise" from the front, back, engine area. Is it only when in motion or is noise evident when parked and motor RPM raised? Has anything been done to the car recently? What if any maintenance has been done?

[tisilrad]

My first guess would be fuel filter needs to be changed, I have seen this problem before, though not with 928's. The 'flappy" valve may be acting up also, maybe a vacuum leak to the actuator or feeding the actuator, corroded/bad connection to the solenoid controlling the actuator.

[Big Load]

thanks guys
OK still working on figuring out if noise is from front or back. so will update in a bit.

But the flapping sound only comes when i drive not when stationary at idle. it occurs when i put my foot on the throttle. its really hard to explain. also i'm not sure if this is related but if i start her up and leave to idle she idles very low around 700.

so far the only work i have had done on the car is a service ie spark/oil/air filters, the timing belt and water pump has just been replaced, the maf has been rebuilt, and the flex plate re positioned.

my next step was to concentrate on the vacuum pipes but then this seems more important.

how can i tell if it is the fuel filter/ pump?? or something else. what can i check.
I think I will make a video and post it that would be better to explain.

I'll check the actuator today....how do i do that??

[tisilrad]

the fuel filter shoud be replaced every 15k miles i would think, there is a fuel pressure check point on the front of the passengers side fuel rail, you would have to attach a gauge to check fuel pressure. Check for vacuum at the flappy valve acuator and check to see if it is working by letting the engine run for a few minutes to build vacuum in the reservoir and then shutting the engine down. then you would pull the rubber cover on the top of the manifold to reveal the top of the flappy valve shaft. With someone inside the car operating the key(the car in park or neutral with the emergency brake applied), turn to the start position, the shaft should rotate in a testing procedure prior to engine start assuming there is enough vacuum in the reservoir to operate the flappy valve(the diaphram control under the intake works off engine vacuum). Also with the engine runnning the valve operation can be checked by revving the engine in a short throttle "blip" above 4000 rpm and you can observe that the shaft will rotate. hope this helps.

[tisilrad]

please note that in testing fuel pressure, you can have proper pressure even with a poor fuel filter. the filter would limit performance only when the vehicle was "under load"..i.e. pulling up a hill or accelerating hard in high gear.It is thus difficult to diagnose a fuel filter partial failure/blockage.

[Big Load]

OK i need to digest this info so i can decide on how to start this fix. I did 3 videos of the sounds I am getting and stuck them on youtube 'under porsche 928 running issues'

they are not the best videos as they are my first. see what you think

porsche 928 running issues - YouTube

IMG 6643 - YouTube

IMG 6644 - YouTube

[turborat]

Sounds like a misfire to me. Bad spark plug or wire. These engines will lay over with just one bad plug or wire. Run the engine at idle and remove the wire boot from the spark plugs one at a time. The one that has no change on the idle is the bad one. Start simple and go from there. Ignition caps, rotors, wires and plugs are the simple stuff. Can also look under the hood when dark and look for arching. The tick sound you hear may be the electrical arc of the ignition because a wire has gone bad and arcing to engine earth.

[jstobo]

Troubleshooting guide. If you haven't already, pull the injectors and have them cleaned first. Dirty injectors will cause all sorts of running problems.

[tisilrad]

I agree with turborat, after watching the videos it sounds like you may have a spark plug wire arcing. this will cause your problem as well as the smell of a rich running engine and bad performance under load. Follow turborats advice on how to troubleshoot the problem. Is the timing belt light working? have you had it retensioned as needed? I have heard timing belts make this ticking noise but to affect performance the timing belt would have to have slipped and affected engine timing..not likely in your case a these are interference engines and this probabply would prevent running..

[Big Load]

wow OK
SO MORE INFO to digest.. sparks where just changed a month back. but i will check all these things. no timing belt light on as that was also done a month back with the water pump.
let me just get my head around what i need to do and i will be back. thanks everyone so far though.

[AirtekHVAC]

Not that I have much to add, but I replaced my original wires with new aftermarket, and she ran terrible...could not get her tuned....replaced them 1at a time wit the old, and found 2 of the new not working...think the connectors are bad....put the old wires all back on...she runs more better now....

[Big Load]

hi
ok spark plugs are good so are the wires. now to check temperature sensor and flappy think.

[Big Load]

hi can anyone recommend this tool for checking vacuum etc:

Gunson G4103 Lo Gauge Vacuum Tester All Petrol Engines

Gunson G4103 Lo Gauge Vacuum Tester All Petrol Engines | eBay

[MainePorsche]

Originally Posted by Big Load

hi guys
when i accelerate my car feels heavy not impulsive. heavy is the only way i can describe it. or the response on pressing the throttle is delayed by a few seconds. does that make sense?? almost as though she is choked!!and needs more gas to move. could something be blocked? I haven't got around to changing the fuel lines yet or changing the vacuum lines. could that be the cause?

gearbox seems OK, no knocking, high revs or issues i can see or tell.

Then when i do move i hear what i can only describe as a flapping sound not a smooth acceleration sound. if i take my foot off the accelerator the sound goes away. maybe exhaust?? but it doesn't sound blown

help

Don't know about the flapping sound you mention.
You've gone through some of the basics - fuel filter, plugs, ignition cables, coil cables with their proper positioning.
Is your TPS (Throttle Position Sensor) set right ?
First, approach the cable quad and with engine OFF manually pull the throttle cable forward gently. If set correctly, as soon as it moves forward you should here a click from the TPS. The sound emanates from under the intake at about the same position as the cable quad. If you have to pull on the cable any distance in order to hear the click, your throttle cable is not set correctly to the TPS. If you have to reset, pop the cup off the ball on the throttle cable union with the quad. The locking nut is 7 mm if I remember correctly, and the scores on the cup neck hold and 8 mm wrench. Adjust appropriately. Once this is done you will have to reset your transmission kickdown cable, or Bowden cable. For descriptive purposes, if you tighten the throttle cable you in essence loosen the Bowden cable and vice versa. So, if you tighten the throttle cable by two turns of the cup, do the same for Bowden cable if comfortable with the timing of your shifts (as you have not complained about shifting timing, I am going to assume the Bowden is set correctly to your liking). After you do this then make sure your cruise control cable has a little slack in it. Lastly, adjust the pedal cable to a non tense and non slacked lie (or to your particular liking). I'll attach a pic of the cable quad so you know where you are.
Best Wishes.

[Big Load]

wow thanks for that last post
I was wondering about adjusting these but didn't touch them as I didn't know enough about what needed to be done. I will try what you told me this weekend and get back to you. on a last note by adjusting the peddle cable will that make the accelerator peddle lighter or just more responsive. I ask this as my peddle is tight/ heavy to push rather than soft and responsive

[MainePorsche]

Originally Posted by Big Load

wow thanks for that last post
I was wondering about adjusting these but didn't touch them as I didn't know enough about what needed to be done. I will try what you told me this weekend and get back to you. on a last note by adjusting the peddle cable will that make the accelerator peddle lighter or just more responsive. I ask this as my peddle is tight/ heavy to push rather than soft and responsive

You can adjust the pedal cable to your liking, but just finesse it. Extremes aren't good on the 928 and you will monkey with your throttle-Bowden cable relationship. Remember any adjustments at the cable quad go in this order of priority: Throttle cable 1st - Bowden 2nd - cruise then pedal to liking.
Best Wishes.
Craig

[Big Load]

sorry forgive me for my ignorance but the kickdown cable is the same as the bowden cable??