Weird flatspot at 4600rpm, can't 'break through' it in 4th Options

[nebreitling]

Thanks for the info. lucky me my german's actually pretty good (IMG:style_emoticons/default/smilie_flagge6.gif)

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. (IMG:style_emoticons/default/beerchug.gif)

nathan

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

[RustyWa]

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.

[nebreitling]

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 ... (IMG:style_emoticons/default/smile.gif)

you suckers have fun at work!! (IMG:style_emoticons/default/laugh.gif)

[SirAndy]

ahh, being able to work on the 914 on weekday afternoons: one of the joys of grad school ... (IMG:style_emoticons/default/smile.gif)

you suckers have fun at work!! (IMG:style_emoticons/default/laugh.gif)

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! (IMG:style_emoticons/default/laugh.gif)
Andy

[seanery]

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! (IMG:style_emoticons/default/chatsmiley.gif)

[Anton]

it seems like if the FI timing were off that i would feel that through the whole engine range?

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?

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.

[Howard]

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???

[nebreitling]

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

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!! (IMG:style_emoticons/default/lol3.gif)

[nebreitling]

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.

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

[airsix]

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

(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.

[nebreitling]

Ahhh!!! that sounds much more logical (IMG:style_emoticons/default/blink.gif)

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....

[Howard]

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?

[Andyrew]

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