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> Weird flatspot at 4600rpm, can't 'break through' it in 4th
nebreitling
post Aug 7 2003, 07:11 PM
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hi all

i've discovered a weird ignition/fuel system quirk in my '75 2.0, which has probably been going on since i've owned it (3 months) -- just haven't noticed it.

the engine has a flatspot at ~4600rpm -- it feels like the fuel cuts in and out to keep the engine below this speed. now, i can 'break through' it in 1st --> 3rd gear, it just pauses and stumbles a bit at 4600, then moves merrily along toward redline. but in 4th (and 5th, i presume), it feels like i don't have enough power/momentum to 'break through it'.

2 months ago, car had a full tune up, valves adjusted, etc. airpump removed, air injector jets plugged. aside from this quirk, it runs smoothly and strong.

does anyone have suggestions for things to check? (IMG:style_emoticons/default/confused24.gif)

nathan
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RustyWa
post Aug 7 2003, 07:20 PM
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Nathan,

I had a problem recently where I had a stumble during acceleration. It turned out to be my TPS. I got a new one from European Automotive Specialists www.europeanautomotive.com for $85. Cured the stumble.

For testing, I've heard you can disconnect the TPS and see if that cures your problem.
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SirAndy
post Aug 7 2003, 07:21 PM
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uhm, do you have a rev-limiter? hmmm, that would shut off in all gears tho. i threw mine out a while ago ...

Andy
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nebreitling
post Aug 7 2003, 07:43 PM
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QUOTE(SirAndy @ Aug 7 2003, 05:21 PM)
uhm, do you have a rev-limiter? hmmm, that would shut off in all gears tho. i threw mine out a while ago ...

Andy

i don't know -- where would i find the rev-limiter? (IMG:style_emoticons/default/smilie_flagge6.gif)
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Qarl
post Aug 7 2003, 08:00 PM
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I second the throttle position sensor. Remove the throttle body, remove the cover off of the TPS and clean out all the gunk out inside. If there isn't major wear (grooves in the contacts) then it might work better once clean... of not, then replace.

Cleaning out tons of gooped up oil helped my '74 1.8L run better!

Karl
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nebreitling
post Aug 7 2003, 08:02 PM
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QUOTE(RustyWa @ Aug 7 2003, 05:20 PM)


For testing, I've heard you can disconnect the TPS and see if that cures your problem.

TPS = ?

TemPerature Sensor? if so, did you replace the Cylinder Head Temperature Sensor (Temp Sensor II) or the Temperature Sensor I?

or perhaps it's the Throttle Switch? (i'm thinking Throttle Position Switch, TPS?) if so, $85 is a good deal (IMG:style_emoticons/default/clap56.gif)

thanks, gentlemen
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nebreitling
post Aug 7 2003, 08:02 PM
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whoops, never mind!!
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nebreitling
post Aug 7 2003, 08:05 PM
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über-cool

will check out the status of my TPS. this site rocks (IMG:style_emoticons/default/aktion035.gif)
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Howard
post Aug 7 2003, 08:17 PM
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What a great group. And psychic! I was just about to post the same question about my 73 2.0. Have ordered the DIY manuals but not here yet. Where is the TPS and how can it be bypassed for testing?
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Qarl
post Aug 7 2003, 08:21 PM
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Save your $ on the manuals...

click here Save your $$$
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nebreitling
post Aug 7 2003, 08:24 PM
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QUOTE(Howard @ Aug 7 2003, 06:17 PM)
What a great group. And psychic! I was just about to post the same question about my 73 2.0. Have ordered the DIY manuals but not here yet. Where is the TPS and how can it be bypassed for testing?

follow the accelerator cable to the intake and you'll find it. it has some electrical connections and is adjusted on two screws.

i have no idea how this could be bypassed (IMG:style_emoticons/default/confused24.gif) anyone

and, WELCOME!!! (IMG:style_emoticons/default/beerchug.gif)

looks like this


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SirAndy
post Aug 7 2003, 09:11 PM
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QUOTE(nebreitling @ Aug 7 2003, 06:43 PM)

i don't know -- where would i find the rev-limiter? (IMG:style_emoticons/default/smilie_flagge6.gif)

you'll find it inside the dizzy.
if you have a rev-limiter, the rotor will have a little spring built in that shuts off the ingnition at a certain RPM ...

but again, that would affect any gear.
but it can't hurt to check anyways ...

Andy
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airsix
post Aug 7 2003, 09:45 PM
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QUOTE(nebreitling @ Aug 7 2003, 06:24 PM)
i have no idea how this could be bypassed (IMG:style_emoticons/default/confused24.gif) anyone

If you're talking about the TPS, you just unplug it.
If you're talking about a rev-limiting rotor (in the distributor) you can't bypass it - you have to live with it or get a new rotor (a non-rev-limiting rotor is just a few bucks).
-Ben

ps - If you're wondering how to tell between a rev-limiting rotor and a non-revlimiting rotor: Haynes manual has pictures of both. Maybe someone will post.
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nebreitling
post Aug 7 2003, 10:34 PM
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oh.... (IMG:style_emoticons/default/blink.gif)

i need to read up more on my djet -- i thought that unplugging the throttle position valve would cause the FI not to run properly. so what in hell does the tps do, then? (IMG:style_emoticons/default/blink.gif) (IMG:style_emoticons/default/blink.gif)

(IMG:style_emoticons/default/beerchug.gif)
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Howard
post Aug 7 2003, 10:39 PM
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Again, thanks everybody. I pulled the TPS plug and it helped but didn't cure. Car had been sitting for quite a while..I just bought it 2 weeks ago. Put Techron in the first tank and probably just loosened up some junk. Tank has rust particles inside and will drain and get it hot tanked or replaced as necessary. And another neat thing. Car floods and will not start when cold start injector is connected. Pull plug on that and it starts on first kick. I think it just needs an enema.
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Howard
post Aug 7 2003, 10:53 PM
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kellzey (thanks Karl) sent me to this page about the TPS. Check it out


Attached File(s)
Attached File  914_20FI.pdf ( 68.52k ) Number of downloads: 129
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airsix
post Aug 8 2003, 11:26 AM
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QUOTE(nebreitling @ Aug 7 2003, 08:34 PM)
oh.... (IMG:style_emoticons/default/blink.gif)

i need to read up more on my djet -- i thought that unplugging the throttle position valve would cause the FI not to run properly. so what in hell does the tps do, then? (IMG:style_emoticons/default/blink.gif) (IMG:style_emoticons/default/blink.gif)

(IMG:style_emoticons/default/beerchug.gif)

It won't run properly. You don't want to drive around without the TPS working - you won't have any accel enrichment (like a accel valve on a carb that squirts extra fuel when you quickly press the throttle). Unplugging it is just a way of testing to see if it's at fault - if at fault it'll send weird signals most often resulting in slight surging or bucking when driving at a steady speed.

-Ben M. (ps - I don't think the problem is the TPS but I could be wrong)
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Demick
post Aug 8 2003, 11:49 AM
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Howard. You live in a warm climate. Leave your cold start valve disconnected. I leave mind disconnected year round. It shouldn't get cold enough there to cause the cold start valve to activate anyway, so the fact that yours seems to be getting activated indicates that the temperature sensor that controls the cold start valve is defective.

Demick
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Howard
post Aug 8 2003, 12:10 PM
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Demick. Thanks, I have reached the same conclusion. Wind chill here got down to 66 last night.

But something is wrong. Advise pulling all out to clean? Put in a new fuel filter and assume that will trap most of the gunk.
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Anton
post Aug 8 2003, 12:19 PM
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IMPO these things mostly come down to a maintenance deficit.

Your car had a "full tune-up" but does that include:
- New FI trigger points? A very likely candidate for your problem BTW.
- Fuel pressure check? Important determinant of FI system function.
- Fuel injector clean-up? Check on a test bence and clean ultrasonically and/or replace where needed.
- New condenser? Sould be routinely exchanged every couple of years.
- Vacuum hose check up and/or renewal? Vacuum leaks are infamous for all sorts of engine trouble.

When these measures don't work out go for the pressure sensor, TPS, sticky distributor plate (!), etc.

There are various manuals on the web on D-jet trouble shooting. I believe there is one on the PP website and here is what Mittelmotor says (eat your heart out; it's in German (IMG:style_emoticons/default/laugh.gif) ).

--------------------------------------------------------------------------------

Ruckeln im 914

Die drei wichtigsten Teile der Einspritzung sind der Druckfühler, die Auslösekontakte und der Drosselklappenschalter.

Die Funktionsfähigkeit dieser drei Bauteile beeinflußt ganz erheblich die Laufkultur und den Benzinverbrauch des Motors. Wer nicht die Möglichkeit hat, die Funktion dieser Teile zu messen, sollte auf folgende Symptome seines Motors achten:

defekter Druckfühler:

- starkes Ruckeln bei konstantem Gas
- hoher Benzinverbrauch
- Leistungsmangel

defekte Auslösekontakte:

- Aussetzer nur bei warmem Motor
- Heißstartschwierigkeiten
- Leistungsmangel

defekter Drosselklappenschalter:

- leichtes Ruckeln bei konstantem Gas
- Beschleunigungsloch bei plötzlichem Gasgeben

--------------------------------------------------------------------------------

Anyway, they name three candidates for your problem: the pressure sensor, FI trigger points, and the TPS.

Good luck.
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