cruising hesitation |
|
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. |
|
cruising hesitation |
prrt1 |
Aug 21 2022, 03:09 PM
Post
#1
|
Newbie Group: Members Posts: 6 Joined: 14-August 22 From: stockton, nj Member No.: 26,774 Region Association: North East States |
Need help please! I have a certain car (someday it will be a Porsche) with D-jet, rebuilt manifold air pressure sensor, new injectors, new fuel pressure regulator, and a new PC board in the Throttle Position Switch. While cruising, I get a hesitation (pretty severe) that feels like some is flipping a switch off/on. Wondering if anyone can give me an idea what might be wrong? I hope my terminology is OK..and I searched but no results...
Thanks for any help. |
mgphoto |
Aug 21 2022, 03:20 PM
Post
#2
|
"If there is a mistake it will find me" Group: Members Posts: 1,339 Joined: 1-April 09 From: Los Angeles, CA Member No.: 10,225 Region Association: Southern California |
Clean the trigger points in the base of the distributor.
|
StarBear |
Aug 21 2022, 03:27 PM
Post
#3
|
Senior Member Group: Members Posts: 1,905 Joined: 2-September 09 From: NJ Member No.: 10,753 Region Association: North East States |
Or maybe water/moisture in gas. Happens (to me) this time of year with partial tank of gas and high humidity then condensation overnight. Fill up tank with a quality gas.
|
brant |
Aug 21 2022, 03:41 PM
Post
#4
|
914 Wizard Group: Members Posts: 11,632 Joined: 30-December 02 From: Colorado Member No.: 47 Region Association: Rocky Mountains |
Maybe double check the TPS position with an ohm
|
BeatNavy |
Aug 21 2022, 03:44 PM
Post
#5
|
Certified Professional Scapegoat Group: Members Posts: 2,924 Joined: 26-February 14 From: Easton, MD Member No.: 17,042 Region Association: MidAtlantic Region |
This one has a lot of potential causes. It could be fuel delivery related or ignition related.
On the fuel side: Dirty fuel tank "sock" filter Clogged fuel filter Problem with fuel pump Loose injector grounds (check the 3 prongs at back of engine case) Loose injector connectors Clogged injectors (not likely in your case with new injectors) Bad or misadjusted trigger points Bad, dirty, improperly adjusted TPS Ignition side: Loose spark plug wires Something wrong with or in distributor -- check ground strap, check condition of dizzy cap and rotor, make sure points are in good shape and adjusted properly You can eliminate the TPS as a variable by unplugging the connector at the TPS. Car won't accelerate as well, but it will run ok and you can see if the problem persists. Try the easy things first: check injector connections, injector grounds, spark plug wires, and condition of dizzy components. There are a LOT of threads on this. Try searching again "bucking while cruising" http://cse.google.com/cse?cx=0024083458981...772:ajvfxschcgc |
prrt1 |
Aug 21 2022, 04:31 PM
Post
#6
|
Newbie Group: Members Posts: 6 Joined: 14-August 22 From: stockton, nj Member No.: 26,774 Region Association: North East States |
Excellent suggestions everyone...thanks very much!
|
emerygt350 |
Aug 21 2022, 05:06 PM
Post
#7
|
Advanced Member Group: Members Posts: 2,131 Joined: 20-July 21 From: Upstate, NY Member No.: 25,740 Region Association: North East States |
Is it only cruise and only when you are just barely keeping the throttle open?
And is it the stock distributor? |
930cabman |
Aug 21 2022, 05:09 PM
Post
#8
|
Advanced Member Group: Members Posts: 3,128 Joined: 12-November 20 From: Buffalo Member No.: 24,877 Region Association: North East States |
This one has a lot of potential causes. It could be fuel delivery related or ignition related. On the fuel side: Dirty fuel tank "sock" filter Clogged fuel filter Problem with fuel pump Loose injector grounds (check the 3 prongs at back of engine case) Loose injector connectors Clogged injectors (not likely in your case with new injectors) Bad or misadjusted trigger points Bad, dirty, improperly adjusted TPS Ignition side: Loose spark plug wires Something wrong with or in distributor -- check ground strap, check condition of dizzy cap and rotor, make sure points are in good shape and adjusted properly You can eliminate the TPS as a variable by unplugging the connector at the TPS. Car won't accelerate as well, but it will run ok and you can see if the problem persists. Try the easy things first: check injector connections, injector grounds, spark plug wires, and condition of dizzy components. There are a LOT of threads on this. Try searching again "bucking while cruising" http://cse.google.com/cse?cx=0024083458981...772:ajvfxschcgc (IMG:style_emoticons/default/agree.gif) could be as simple as a clogged fuel filter. Keep the faith and let us know of your results |
prrt1 |
Aug 22 2022, 03:55 PM
Post
#9
|
Newbie Group: Members Posts: 6 Joined: 14-August 22 From: stockton, nj Member No.: 26,774 Region Association: North East States |
Original dizzy, ca. 1975. I have suspected the trigger points, took them out, cleaned, and seem to be OK per Dr. D-jet specs, but I think the rub blocks are at their limit. New fuel filter, checked the pump inlet and it seems to be OK. Crane ignition (no points.)
The bucking happens at about 2000 rpm, 50 mph or so, but it has happened on acceleration also. I'm getting much good input from everyone, will try a few things. I will reveal the car is a 1974 BMW 3.0CS into which I installed D-jet from a '75 coupe. Joined this group because, well, Porsche guys are as fanatical as BMW guys and hope there is some knowledge I can pick up... Thanks. |
DRPHIL914 |
Aug 22 2022, 04:31 PM
Post
#10
|
Dr. Phil Group: Members Posts: 5,768 Joined: 9-December 09 From: Bluffton, SC Member No.: 11,106 Region Association: South East States |
Maybe double check the TPS position with an ohm (IMG:style_emoticons/default/agree.gif) if you use an eraser to clean the TPS board, it may clear this up,, i had exactly the same issue that no matter what i did it didnt clear up until I cleaned that off. If the tracers have marked the board too deep and you cant just clean them off, Dave Sprinkle makes new boards. Phil |
emerygt350 |
Aug 22 2022, 04:55 PM
Post
#11
|
Advanced Member Group: Members Posts: 2,131 Joined: 20-July 21 From: Upstate, NY Member No.: 25,740 Region Association: North East States |
He has a new board in the tps. I am starting to think you really need to adjust it by hand in some cases. I was having to do this recently as well. By that I mean setting it 'correctly' on the bench doesn't always cut it.
|
prrt1 |
Aug 3 2023, 02:27 PM
Post
#12
|
Newbie Group: Members Posts: 6 Joined: 14-August 22 From: stockton, nj Member No.: 26,774 Region Association: North East States |
Welp, a year later and I still have hesitation, sometimes severe (as though the engine momentarily shuts off, it bucks, but doesn’t stall), I tested everything as suggested herein. I think I have narrowed the problem down to the TPS: My car runs OK with the TPS disconnected, but as soon as I plug it in, I get burps and eventually more severe hesitation. I have fiddled with the TPS (it has a PC board only a couple of years old) to no end. I’m thinking it might be a bad wire to the ECU, but before I rewire it I was wondering… if everything is OK without the TPS, what do I need it for? Thanks for all your help.
|
brant |
Aug 3 2023, 02:42 PM
Post
#13
|
914 Wizard Group: Members Posts: 11,632 Joined: 30-December 02 From: Colorado Member No.: 47 Region Association: Rocky Mountains |
car normally runs without TPS
but does not run well TPS is important throttle information for the "computer" adding additional fuel... you need it. did you try to set it correctly with an OHM meter? did you try to clean the board inside of the TPS housing then next replace the board if you have done the above and reset it correctly to baseline with an Ohm meter |
windforfun |
Aug 3 2023, 02:47 PM
Post
#14
|
Senior Member Group: Members Posts: 1,822 Joined: 17-December 07 From: Blackhawk, CA Member No.: 8,476 Region Association: None |
Did you align the new TPS board exactly like the old one? Are the two boards geometrically identical?
|
emerygt350 |
Aug 3 2023, 08:54 PM
Post
#15
|
Advanced Member Group: Members Posts: 2,131 Joined: 20-July 21 From: Upstate, NY Member No.: 25,740 Region Association: North East States |
Are you sure this isn't a lean miss?
|
TX914 |
Aug 4 2023, 05:43 AM
Post
#16
|
Alan-B Group: Members Posts: 172 Joined: 27-July 14 From: USA Member No.: 17,689 Region Association: None |
May want to check CHT sensor and CHT lead wire for wear/corrosion. Assuming lead is good, a quick test for CHT is with engine warm, remove lead and ground it.
|
Tom_in_NH |
Aug 4 2023, 12:49 PM
Post
#17
|
Newbie Group: Members Posts: 9 Joined: 21-August 22 From: FL Member No.: 26,792 Region Association: None |
Classic symptoms of a D-Jet TPS issue. Very detailed investigation here:
https://sw-em.com/bosch_d-jetronic_TPS_investigation.htm |
windforfun |
Aug 4 2023, 01:09 PM
Post
#18
|
Senior Member Group: Members Posts: 1,822 Joined: 17-December 07 From: Blackhawk, CA Member No.: 8,476 Region Association: None |
(IMG:style_emoticons/default/agree.gif) (IMG:style_emoticons/default/agree.gif) (IMG:style_emoticons/default/agree.gif) I had the same problem some years back. I replaced the TPS with a new one & aligned it just like the old one (which was badly worn). The problem was solved. (IMG:style_emoticons/default/beerchug.gif) (IMG:style_emoticons/default/beerchug.gif) (IMG:style_emoticons/default/beerchug.gif) |
prrt1 |
Oct 12 2023, 03:25 PM
Post
#19
|
Newbie Group: Members Posts: 6 Joined: 14-August 22 From: stockton, nj Member No.: 26,774 Region Association: North East States |
I have found a “solution” to my cruising hesitation and severe bucking problem in my D-jet equipped BMW (I’m writing to 914 World because you guys set me in the right direction. D-jet BMWs are few and far between in our world.)
Anyway, the posts in 914 World gave excellent information (especially Tom in NH) about this problem but no one seems to have identified how to fix it. My solution was to cut wire #9 between the TPS and the ECU. Wire #9 connects one of the sawtooth traces in the TPS. I found this by chance, but the severe bucking and cruising hesitation is gone, except for a very minor stumble when shifting from 1st to 2nd. Also the hard starting-when-warm problem has disappeared. I don’t know why this fixed the problems, but I running with it for now. I want to thank 914 World for all the help they have provided in my 2-year struggle to fix this problem. |
rjames |
Oct 12 2023, 03:37 PM
Post
#20
|
I'm made of metal Group: Members Posts: 3,948 Joined: 24-July 05 From: Shoreline, WA Member No.: 4,467 Region Association: Pacific Northwest |
Original dizzy, ca. 1975. I have suspected the trigger points, took them out, cleaned, and seem to be OK per Dr. D-jet specs, but I think the rub blocks are at their limit. New fuel filter, checked the pump inlet and it seems to be OK. Crane ignition (no points.) The bucking happens at about 2000 rpm, 50 mph or so, but it has happened on acceleration also. I'm getting much good input from everyone, will try a few things. I will reveal the car is a 1974 BMW 3.0CS into which I installed D-jet from a '75 coupe. Joined this group because, well, Porsche guys are as fanatical as BMW guys and hope there is some knowledge I can pick up... Thanks. Cutting wires isn't a good fix. I'll have to go find a wiring diagram to see what that wire does. But I just re-read one of your original posts where you said the bucking happens at 2000 RPMs at 50 MPH. Is that during acceleration or while you're 'crusing'? Because that RPM is way to low to be crusing at, and I would expect the car to buck a bit and generally be very unhappy if you're crusing at 2k RPMs. You should be at 3K RPMs or higher. |
Lo-Fi Version | Time is now: 31st May 2024 - 11:30 PM |
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 ... |