Pelican Parts
Parts Catalog Accessories Catalog How To Articles Tech Forums
Call Pelican Parts at 888-280-7799
Shopping Cart Cart | Project List | Order Status | Help



Go Back   Pelican Parts Forums > Porsche Forums > Porsche 924/944/968 Technical Forum


Reply
 
LinkBack Thread Tools Rate Thread
Author
Thread Post New Thread    Reply
Registered User
 
princetonprep17's Avatar
 
Join Date: Dec 2004
Location: DC
Posts: 160
Hesitations at speeds above 75, why?

I posted this a little while back and it have stopped for awhile but while I was on my way back from Spring Break it started to do it again. What happens is the car will ride fine for about 2 hours or so and then it will start in with this hesitation. I get around 75-80mph and the car will start to cut out like you abruptly let off the gas and then go back on it. The mpg gauge go to 60 and then back down like it would if you let off the gas and then got back on it. The car doesn't surge like this at any other speeds. Could this be fuel related? I would imagine (though I don't know never having experienced a faulty fuel pump) that if the fuel pump was bad, then it would be having these hesitations throughout the rpm range. What about injectors? I use fuel injector cleaner regularly (usually every 2 fill ups). Could it be something in the injectors? What about the DME or a faulty sensor (o2 sensor I know is yet to be changed). What about a backup in the exhaust system. Could this possibly cause a problem like that? I checked my grounds (except for on the starter, couldn't get to it at the time). Bad ground maybe?
__________________
Current:
70 Mustang Mach 1, 428SCJ, 4 spd, 3.55 Detroit Locker, DB, PS
11 BMW 335is, DCT
Old 03-18-2005, 07:04 AM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #1 (permalink)
Registered User
 
Join Date: May 2004
Location: Brandon FL
Posts: 371
does this happen at any specific rpm range or just at 75-80 mph?
__________________
Rick
99 996C4
06 525XI
87 944S - Sold
77 924 - Sold
Old 03-18-2005, 08:05 AM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #2 (permalink)
Registered User
 
princetonprep17's Avatar
 
Join Date: Dec 2004
Location: DC
Posts: 160
oh sorry, no its just at and above 75 mph. It wont do it at any other speeds below that in any other gears. I meant to try and downshift to fourth to see if that had any impact on it. Every other speed up to 75 is just fine. I could cruise at 70 all day without a problem (and had to for about 2 hours with no problems)
__________________
Current:
70 Mustang Mach 1, 428SCJ, 4 spd, 3.55 Detroit Locker, DB, PS
11 BMW 335is, DCT
Old 03-18-2005, 09:30 AM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #3 (permalink)
Registered User
 
Rmills944's Avatar
 
Join Date: Oct 2004
Location: Memphis
Posts: 340
Send a message via AIM to Rmills944 Send a message via Yahoo to Rmills944
I was thinking TPS, but that would happen in all gears, just while the accelerator was at a certain point.
I'd definately change the o2 sensor since it's $17 at Autozone and takes about 5 minutes to change. The AFM could be a culprit, but I don't see why that would be only above 75MPH.
__________________
Ryan
'84 944 moneysucker edition (SFR, Corbeaus, etc.)
'02 Jetta TDI 280Lb/Ft 145Hp @ wheels. RC2 PP357's
Old 03-18-2005, 10:10 AM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #4 (permalink)
Registered User
 
princetonprep17's Avatar
 
Join Date: Dec 2004
Location: DC
Posts: 160
Ya, that's what didnt make sense to me. It only does it at that speed but at no other speed below it and it runs great regularly. It's been driving me nuts trying to figure it out and I was hoping maybe ya'll could shed some light on it. Thanks!
__________________
Current:
70 Mustang Mach 1, 428SCJ, 4 spd, 3.55 Detroit Locker, DB, PS
11 BMW 335is, DCT
Old 03-18-2005, 02:46 PM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #5 (permalink)
Registered User
 
Join Date: May 2001
Location: Markham, Ontario, Canada
Posts: 429
Wiper arm in the AFM is sitting on a weak spot on the resitive material. Check the Wilk site if it is still up, there is a description on how to fix this.
__________________
Mark
'86 944NA
'10 VW Golf 2.5 5sp
'99 BMW 540i Sport Wagon
Old 03-18-2005, 07:26 PM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #6 (permalink)
Registered User
 
Join Date: Mar 2004
Location: Leesburg, Georgia, USA
Posts: 1,567
Garage
If it happens at a specific rpm, record this rpm value.
Then backprobe the AFM terminals 7 (output voltage) and 6 (ground) at that rpm with engine running and observe the output for stability.

You are looking for a steady output voltage depending on how steady you can hold the rpm. If it is erratic, the AFM has some dead spots at that particular resistive coating on the pcb board inside.

There is a fix to this at Clark's Garage also at FRWilk's website. Or you can get a new AFM.
__________________
1993 964 C2 still makes me smile
1996 318ti (280k miles)
2011 Silverado for hauling (32k miles) - SOLD
2018 Suburban Z71
Old 03-19-2005, 02:57 AM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #7 (permalink)
Registered User
 
princetonprep17's Avatar
 
Join Date: Dec 2004
Location: DC
Posts: 160
I will have to do it when I go home for the summer from college then because I dont have a voltmeter up here. I will check both sites to see how to fix and what not. Is this a fairly common problem with the 944's?
__________________
Current:
70 Mustang Mach 1, 428SCJ, 4 spd, 3.55 Detroit Locker, DB, PS
11 BMW 335is, DCT
Old 03-19-2005, 09:40 AM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #8 (permalink)
Registered User
 
Join Date: Jan 2004
Location: Upstate NY
Posts: 569
fuel filter? Don't forget the spark, hesitation can be fuel or spark. Wires , coil, rotor, cap and plugs are all easy to check while chasing this problem, good luck.
__________________
AJF

1998 Glacier White Boxster
1971 Fiat 124 Spyder
1999 Mercury Mountaineer
Old 03-19-2005, 10:57 AM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #9 (permalink)
Registered User
 
princetonprep17's Avatar
 
Join Date: Dec 2004
Location: DC
Posts: 160
Fuel filter, wires, cap and rotor are all brand new items (not to say they are not faulty however). I will probably replace the coil in the next few days because it is fairly inexpensive. My original thoughts were fuel or spark as well however it only happens at high speeds.
__________________
Current:
70 Mustang Mach 1, 428SCJ, 4 spd, 3.55 Detroit Locker, DB, PS
11 BMW 335is, DCT
Old 03-19-2005, 03:42 PM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #10 (permalink)
Registered User
 
Join Date: Jan 2004
Location: Upstate NY
Posts: 569
High speed manifestation doesn't rule out spark. On one of my motorcycles the same "breaking up" was happening at high rpm. It turned out to be the plugs and they weren't that old...
__________________
AJF

1998 Glacier White Boxster
1971 Fiat 124 Spyder
1999 Mercury Mountaineer
Old 03-19-2005, 03:57 PM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #11 (permalink)
Reply

Thread Tools
Rate This Thread
Rate This Thread:

 


All times are GMT -8. The time now is 11:42 PM.


 
Powered by vBulletin® Version 3.8.7
Copyright ©2000 - 2019, vBulletin Solutions, Inc.
Search Engine Optimization by vBSEO 3.6.0
Copyright 2018 Pelican Parts, LLC - Posts may be archived for display on the Pelican Parts Website -    DMCA Registered Agent Contact Page
 

DTO Garage Plus vBulletin Plugins by Drive Thru Online, Inc.