Home  |  Forums  |  914 Info  |  Blogs
 
914World.com - The fastest growing online 914 community!
 
Porsche, and the Porsche crest are registered trademarks of Dr. Ing. h.c. F. Porsche AG. This site is not affiliated with Porsche in any way.
Its only purpose is to provide an online forum for car enthusiasts. All other trademarks are property of their respective owners.
 

Welcome Guest ( Log In | Register )

 
 Reply to this topicStart new topic
> 2.0 Factory FI - Hesitation Problem, Please help, any ideas where to start ??
913B
post May 16 2011, 01:25 PM
Post #1


Senior Member
***

Group: Members
Posts: 847
Joined: 25-April 05
From: South Bay/SoCal
Member No.: 3,983
Region Association: None
I am trying to help a friend out. The engine hesitates when accelerating in 2nd gear above 3500rpm. Does not occur when cold. Ambient temps > 60F. Did not notice when cold. Check timing ? Injectors ? Dirty air filter ? When this hesitation happens can hear an after burn backfire.

Thanks in advance.
User is offlineProfile CardPM
Go to the top of the page
+Quote Post
zymurgist
post May 16 2011, 01:41 PM
Post #2


"Ace" Mechanic
*****

Group: Members
Posts: 7,411
Joined: 9-June 05
From: Hagerstown, MD
Member No.: 4,238
Region Association: None
Sounds like the famous "bucking" problem. The throttle position switch (TPS) is usually to blame for this. There is a replacement circuit board that one of the members here designed and sells that usually fixes this problem.
User is offlineProfile CardPM
Go to the top of the page
+Quote Post
913B
post May 16 2011, 01:46 PM
Post #3


Senior Member
***

Group: Members
Posts: 847
Joined: 25-April 05
From: South Bay/SoCal
Member No.: 3,983
Region Association: None
QUOTE(zymurgist @ May 16 2011, 12:41 PM) *

Sounds like the famous "bucking" problem. The throttle position switch (TPS) is usually to blame for this. There is a replacement circuit board that one of the members here designed and sells that usually fixes this problem.

Is there any test to confirm this or swap-tronics ?
User is offlineProfile CardPM
Go to the top of the page
+Quote Post
tradisrad
post May 16 2011, 01:59 PM
Post #4


Senior Member
***

Group: Members
Posts: 985
Joined: 11-September 06
From: San Mateo, CA
Member No.: 6,815
Region Association: Northern California
clean the TPS and then follow the pelican article on how to set the TPS.
User is offlineProfile CardPM
Go to the top of the page
+Quote Post
Dave_Darling
post May 16 2011, 02:36 PM
Post #5


914 Idiot
**********

Group: Members
Posts: 14,986
Joined: 9-January 03
From: Silicon Valley / Kailua-Kona
Member No.: 121
Region Association: Northern California
Unplug it to take it out of the circuit. The idle may be a bit ragged or low, and acceleration will suck, but if the bucking is gone you have a pretty good idea that the switch is to blame.

--DD
User is offlineProfile CardPM
Go to the top of the page
+Quote Post
913B
post May 16 2011, 07:23 PM
Post #6


Senior Member
***

Group: Members
Posts: 847
Joined: 25-April 05
From: South Bay/SoCal
Member No.: 3,983
Region Association: None
QUOTE(Dave_Darling @ May 16 2011, 01:36 PM) *

Unplug it to take it out of the circuit. The idle may be a bit ragged or low, and acceleration will suck, but if the bucking is gone you have a pretty good idea that the switch is to blame.

--DD

Stupid question but the car will run with the TPS unplugged ?
I assume in some default value pre-programmed into the ECU. ?

Thanks Again !!
User is offlineProfile CardPM
Go to the top of the page
+Quote Post
Kraftwerk
post May 16 2011, 07:27 PM
Post #7


Member
**

Group: Members
Posts: 195
Joined: 6-September 07
From: Bbbbbrroooklynnn
Member No.: 8,085
Dave Darling seems to know what he is talking about. Give it a try and get back to us..
User is offlineProfile CardPM
Go to the top of the page
+Quote Post
ThinAir
post May 16 2011, 11:03 PM
Post #8


Best friends
****

Group: Members
Posts: 2,542
Joined: 4-February 03
From: Flagstaff, AZ
Member No.: 231
Region Association: Southwest Region
Testing using Dave Darling's technique pinned down this problem as the TPS on my 1.7 and replacing it confirmed it. I may have the same problem now on my 2.0L, but I can't find any member vendors that offer this. Who does this?
User is offlineProfile CardPM
Go to the top of the page
+Quote Post
Dave_Darling
post May 17 2011, 01:39 AM
Post #9


914 Idiot
**********

Group: Members
Posts: 14,986
Joined: 9-January 03
From: Silicon Valley / Kailua-Kona
Member No.: 121
Region Association: Northern California
QUOTE(porsche913b_sp @ May 16 2011, 06:23 PM) *

Stupid question but the car will run with the TPS unplugged ?
I assume in some default value pre-programmed into the ECU. ?


Yes, it runs without the TPS. The TPS is not one of the primary things to figure out mixture, it only changes the mixture under a couple of specific circumstances. One is when the engine is at idle (throttle closed), and the other is when the throttle is being opened up. There is no default value, the lack of a signal is seen as "not at idle, throttle not currently being opened more".

--DD
User is offlineProfile CardPM
Go to the top of the page
+Quote Post
underthetire
post May 17 2011, 08:41 AM
Post #10


914 Guru
*****

Group: Members
Posts: 5,062
Joined: 7-October 08
From: Brentwood
Member No.: 9,623
Region Association: Northern California
QUOTE(ThinAir @ May 16 2011, 10:03 PM) *

Testing using Dave Darling's technique pinned down this problem as the TPS on my 1.7 and replacing it confirmed it. I may have the same problem now on my 2.0L, but I can't find any member vendors that offer this. Who does this?


If i remember correctly, 914rubber had some made.
User is offlineProfile CardPM
Go to the top of the page
+Quote Post
913B
post Sep 9 2011, 01:40 PM
Post #11


Senior Member
***

Group: Members
Posts: 847
Joined: 25-April 05
From: South Bay/SoCal
Member No.: 3,983
Region Association: None
My friend cracked open the TPS and it did not see any tracks signs, he cleaned it up a bit. But he did not try to drive it with it uplugged. Still tracking issue on TPS ? Verified fuel PSI, and inspected the plugs and they were white/gray according to him. I did not see it. The MPS was bad, so a reman from Atlanta is coming. CHT he forgot to write down the exact PN for his 73 2.0L I have read in the rennlist the 73 2.0 is very finicky about the match set of CHT/ECM/MPS and it says it can cause load performance problems.

Is there anything else he can check. Before saying thats how it is because the components may be mismatched ? Oh he also looked into the possibility of AAR as well and replaced the fuel filter too.

Thoughts ?

Thank you
User is offlineProfile CardPM
Go to the top of the page
+Quote Post
TheCabinetmaker
post Sep 9 2011, 02:35 PM
Post #12


I drive my car everyday
*****

Group: Members
Posts: 8,300
Joined: 8-May 03
From: Tulsa, Ok.
Member No.: 666
My 2 cents. The tps is not generaly the culprit in an acceleration miss (unless it is severly misadjusted), but more often it causes the "bucking at cruise" symptom (worn traces). A bad mps will certainly cause the problem you describe, but that would be accompanied by black plugs from the rich condition. I would also suspect the condensor if it has points.

Good luck.
User is offlineProfile CardPM
Go to the top of the page
+Quote Post
TheCabinetmaker
post Sep 9 2011, 02:40 PM
Post #13


I drive my car everyday
*****

Group: Members
Posts: 8,300
Joined: 8-May 03
From: Tulsa, Ok.
Member No.: 666
Don't know if he's still got any, but you can go here for new tps boards

http://www.bradrobertsag.com/product/BRAG-...r-73-76-20.html
User is offlineProfile CardPM
Go to the top of the page
+Quote Post
jsayre914
post Sep 9 2011, 04:31 PM
Post #14


Speed Up !!!
****

Group: Members
Posts: 3,188
Joined: 10-February 08
From: Timonium MD 21093
Member No.: 8,696
Region Association: MidAtlantic Region
I had a hesitation/ bucking in my car.

It turned out the gear at the bottom of the distributor was worn. I swapped out the distributor with another i had in the garage and it ran perfectly.

(IMG:style_emoticons/default/confused24.gif)
User is offlineProfile CardPM
Go to the top of the page
+Quote Post
913B
post Sep 9 2011, 05:18 PM
Post #15


Senior Member
***

Group: Members
Posts: 847
Joined: 25-April 05
From: South Bay/SoCal
Member No.: 3,983
Region Association: None
The idle was fine though, would a mismatched set of components still affect it ? To clarify his MPS did not hold any vacuum. Wouldn't it have more driveabilty problems than the surging with his MPS ?
User is offlineProfile CardPM
Go to the top of the page
+Quote Post
TheCabinetmaker
post Sep 9 2011, 05:34 PM
Post #16


I drive my car everyday
*****

Group: Members
Posts: 8,300
Joined: 8-May 03
From: Tulsa, Ok.
Member No.: 666
Ok, Surging you say? At idle? Thats a lean idle condition possibly corrected by the knob on the ecu, but only if the tps is correctly adjusted. An mps with no vacuum will be dumping large amounts of fuel in the cylinders, causing a major stumble on accel, and make it run like dog poop (what ever that is).
User is offlineProfile CardPM
Go to the top of the page
+Quote Post
Tom
post Sep 9 2011, 06:48 PM
Post #17


Advanced Member
****

Group: Members
Posts: 2,139
Joined: 21-August 05
From: Port Orchard, WA 98367
Member No.: 4,626
Region Association: None
With your description of the plugs ( his ), I would think a lean condition.
Fuel pump, fuel filter, would be my first thing to check.
tom
User is offlineProfile CardPM
Go to the top of the page
+Quote Post
« Next Oldest · 914World Garage · Next Newest »
 

Reply to this topicStart new topic
1 User(s) are reading this topic (1 Guests and 0 Anonymous Users)
0 Members:

 

Display Mode: Standard · Switch to: Linear+ · Switch to: Outline

Track this topic · Email this topic · Print this topic · Subscribe to this forum

- Lo-Fi Version Time is now: 16th May 2024 - 06:08 AM
Invision Power Board v9.1.4 © 2024  IPS, Inc.
All rights reserved 914World.com © since 2002
914World.com is the fastest growing online 914 community!
We have it all, classifieds, events, forums, vendors, parts, autocross, racing, technical articles, events calendar, newsletter, restoration, gallery, archives, history and more for your Porsche 914 ...