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Posted by: nebreitling Aug 7 2003, 07:11 PM

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?

nathan

Posted by: RustyWa Aug 7 2003, 07:20 PM

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.

Posted by: SirAndy Aug 7 2003, 07:21 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

Posted by: nebreitling Aug 7 2003, 07:43 PM

i don't know -- where would i find the rev-limiter?

Posted by: Qarl Aug 7 2003, 08:00 PM

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

Posted by: nebreitling Aug 7 2003, 08:02 PM

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

thanks, gentlemen

Posted by: nebreitling Aug 7 2003, 08:02 PM

whoops, never mind!!

Posted by: nebreitling Aug 7 2003, 08:05 PM

über-cool

will check out the status of my TPS. this site rocks

Posted by: Howard Aug 7 2003, 08:17 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?

Posted by: Qarl Aug 7 2003, 08:21 PM

Save your $ on the manuals...

click here http://www.914world.com/downloads

Posted by: nebreitling Aug 7 2003, 08:24 PM

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 anyone

and, WELCOME!!!

looks like this


Attached image(s)

Posted by: SirAndy Aug 7 2003, 09:11 PM

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

Posted by: airsix Aug 7 2003, 09:45 PM

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.

Posted by: nebreitling Aug 7 2003, 10:34 PM

oh....

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?

Posted by: Howard Aug 7 2003, 10:39 PM

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.

Posted by: Howard Aug 7 2003, 10:53 PM

kellzey (thanks Karl) sent me to this page about the TPS. Check it out


Attached File(s)
 914_20FI.pdf ( 68.52k ) Number of downloads: 130

Posted by: airsix Aug 8 2003, 11:26 AM

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)

Posted by: Demick Aug 8 2003, 11:49 AM

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

Posted by: Howard Aug 8 2003, 12:10 PM

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.

Posted by: Anton Aug 8 2003, 12:19 PM

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 ).

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

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.

Posted by: nebreitling Aug 8 2003, 02:06 PM

Thanks for the info. lucky me my german's actually pretty good

at the end,the article specifically mentions that a defective TPS (ein defekter Drosselklappenschalter) would cause an "acceleration hole" (Beschleunigungsloch). that's the closest symptom to my problem in the article.

didn't even think about FI trigger points. i will investigate, but it seems like the the FI timing were off that i would feel that through the whole engine range?

fuel pressure is fine. almost all new hoses, checked with a little carb cleaner. condenser seems a little unlikely but i'll check using the old 12V "light trick". and it seems like a very good idea to have my fuel injectors ultrasonically cleaned while i'm at it. can i take them to anyplace to have this done?

thanks for all the suggestions, everyone.

nathan

Ben: if you don't think TPS, would you care to conjure a guess?

Posted by: RustyWa Aug 8 2003, 02:35 PM

Another thing to think about Nathan, since you have a '75 and others are suggesting a rev limiting problem. Some '75s, like mine, have a speed limiter box hanging off the FI wiring harness. It's located near the battery. I've heard you can unplug it also and still drive the car...for test purposes.

Hook it back up when you are done.

Posted by: nebreitling Aug 8 2003, 03:11 PM

good idea, thanks! just got home, going out to start working on it right now.

ahh, being able to work on the 914 on weekday afternoons: one of the joys of grad school ...

you suckers have fun at work!!

Posted by: SirAndy Aug 8 2003, 03:14 PM

nope, tiling my new bathroom.

i have my own company,
so i actually have at least as much free time as you do,
plus i get paid $$$.

so long sucker!
Andy

Posted by: seanery Aug 8 2003, 03:21 PM

oh yeah, well I'm a part owner in my company, we don't have any work right now (summer, ya know) and I get all day off AND I get paid!!!

Put a new floor in my bathroom yesterday!

Posted by: Anton Aug 8 2003, 03:24 PM

1. I'm not sure. There are TWO trigger points, so it all depends if only one or both are off-limits. My guess is the symptoms may differ and would not necessarily hav to occur throughout the whole engine range.

2. I have had them done at a local Bosch service center. They needed 3 ultrasonic cycles to get an even output between all 4 injectors! The effect on engine performance was certainly eminent.

They should be checked for leaking under pressure while the solenoid is not activated, spray pattern, output in ml/min (but an even, i.e. relative, output between the four is enough to know IMO) and the little filters inside should be renewed. While you are at it, it wouldn't hurt to renew the rubber O-rings that are holding the injectors.

Have fun.

Posted by: Howard Aug 8 2003, 04:57 PM

or loosely translated in babelfish:

Ruckeln in 914

The three most important parts of injection are the pressure probe, the release contacts and the butterfly valve switches.

The operability of these three construction units affects completely substantially the run culture and the gasoline consumption of the engine.

Who does not have the possibility of measuring the function of these parts should pay attention to the following symptoms of its engine: defective pressure probe: - strong Ruckeln with constant gas - high gasoline consumption - leistungsmangel defective release contacts: - misfires only with warm engine - hot initial problems - leistungsmangel defective butterfly valve switch: - easy Ruckeln with constant gas - acceleration hole with sudden acceleration

It doesn't get all the words but I do get the message. Pretty much rule out fuel line sediment???

Posted by: nebreitling Aug 8 2003, 06:46 PM

not that i'm an expert on this board (new to 914's), but: if your problem manifests as mine does, you could probably rule fuel sediment out as the direct cause -- but it may be an indirect cause or a major problem waiting to happen.

this article is very helpful but is most certainly not completely thorough. as Anton was getting at, basic issues (e.g. ignition/engine problems, vacuum lines -- and i would add -- fuel line sediment) should be addressed before delving into the EFI per se.

"butterfly valve switch?" ha!!

Posted by: nebreitling Aug 9 2003, 08:51 PM

Unplugging my TPS while the engine is running (won't start w/out it) causes it to run like shit. idle drops, definitely a little surging and bucking. are you saying that this is a sign that my TPS is bad or good?

thanks, nathan

Posted by: airsix Aug 9 2003, 09:49 PM

(Somebody with better communicaiton skills than me please feel free to join in and save this)

It is normal for the idle to be poor with the TPS unplugged because the ECU runs a richer mixture at idle and with the TPS unplugged the ECU doesn't know to do this. Unplugging the TPS and idling in the driveway won't tell you anything.

Usually if the TPS is bad then you will get slight surging/bucking when you are cruising down the road at a steady speed (with TPS plugged in). I was saying that at steady speed there should be NO bucking with the TPS unplugged. That's the test - if you have surging/bucking at steady speeds with the TPS PLUGGED IN, and the surging/bucking GOES AWAY when you UNPLUG it, then the TPS is suspect. Note that I am ONLY talking about steady speed where you are not moving the throttle. Witht the TPS unplugged the car will not run well while you are moving the throttle, but should run fine when the throttle is held steady. I hope that makes more sense.

-Ben M.

Posted by: nebreitling Aug 9 2003, 09:55 PM

Ahhh!!! that sounds much more logical

thanks so much for your attention. the more i understand, the more i;m dubious that this is the problem. i'll crack open the distributor tomorrow....

Posted by: Howard Sep 1 2003, 11:56 AM

Ta Daa!

Understand I am not a mechanic. Maybe tinkerer second class at best. This may not be the right way, but my car had same flat spot.

PO said to 'learn to live with it' as he had spent mucho $$$ without success. OK, but it kept getting worse, and in a wider rpm range. New plugs (1 step hotter) and cables did not help.

Last resort. Pulled the injectors and 'backwashed' with compressed air. As the pressure built, the check ball released and a blast of gas and misc. plant life blew out the hose end. Cleaned and replaced all and car runs great right to red line. Can this procedure damage injectors?

Posted by: Andyrew Sep 1 2003, 12:02 PM

I think just running an injector cleaner (little machine) on the injectors would have done the job fine.
But hey, if its fixed, its fixed.. just might have to spring for some injectors sooner, I dono, these other guys are the brains..

I might have the same "flatspot" but unfortunately I wont be driving my car the way you guys will, so it might take me a while to figure out I need to clean them...

my .02 cents

Andrew