FI Problems/considering Weber Options

[Chuckster]

I have been a long time lurker at Rennlist but there is very little discussion on teeners. I think I have found a home for 914 discussion. I would like to thank Geoff for turning me on to your BBS.

This a 914 2L that I hope to use for ITA. The engine is stock and needs to remain stock to keep me legal for SCCA. I realize Webers are technically not legal.

I posted on Rennlist a discussion on switching to Webers. I will just re-post here my FI problems:

The car is leaning out at higher RPMS. I have changed the FI harness, computer, new TPS, put in new injectors. Have put in a known good atmosphere meter. The head temp sensor is on variable resistor so I can fine tune the air-fuel mixture. I have disconnected this and inserted a resistor substitution box. At idle and the resistor box set at say 200ohms the car runs fine. Under heavy load the car begins to get leaning out popping and also begins to miss. When I put in high resistance (2000 ohms) the car runs very rich at idle and under load runs strong, no missing up to about 5000rpm.
5000rpm is my redline so I dont care if it misses at higher than 5000rpms.

I have had lots of help on all these diagnostic tricks including changing the trigger points checked the fuel pressure it is steady if a bit low (29.5psi) through heavy load.

I and others have torn this thing apart so many times, I cant remember if I have checked some simpler things such as the little injector rings at the head. This very well could be the problem. But honestly cant think of anything else to do or check.

I have access to a test carb. off of a '70 914 and will try that. If this fixes the problem, I will put the carbs on. Something my sister thought of which was a crimp in the fuel line. I suppose we could have good pressure and not enough volume.(?)

I do appreciate the input. Any thoughts or experiences would be great. Someone else mentioned the duel 40's. Which does seem to be the set-up.

Thanks again for the suggestions.

Chuckster

[Bleyseng]

Well since I sent you here I will try to answer first,
What year car is it?
What ECU are you running?
What MPS are you running? (the weird grenade lookin thing with one hose)

Adding resistance to the CHT only affects the mix for the idle circuit.
I would check the MPS adjust/calibration. You could be way off on the WOT setting. You should have decent hp until about 4500rpms on a 2.0l engine. After that the hp falls off a cliff according to dyno testing. Some of this is due to the weak stock valve springs, so what springs are you running?

Geoff

[Jeff Krieger]

Don't give up hope on the d-jet. Here's what's possible with a d-jet equipped 2.0. (You can also try this page for d-jet help.)

(IMG:http://persweb.direct.ca/aschwenk/(basically)stock2.0rw-hp.jpg)

[Bleyseng]

Even that guys dyno sheet shows he is running lean at WOT. They need to adjust the MPS or fuel pressure so its under 13 to 1 at WOT to get the power and keep it cool. At several spots the A/F is at 14 to 1 which is lean for these motors.
Geoff

[Chuckster]

Thanks again Geoff for turning me to the 914club.

I have been reading all the interesting discussions on this BBS. Great forum!!!

As I understand what adjusts the A/F at idle is the knob on the ECU. Which is the stock ECU for a '74 2L. The CHT is what tells the ECU what temp the motor is and if cold, sends high resistance that richens the mixture through out the RPM range. Generally full rich is around 400ohms. Forcing it read even higher resistance riches the mixture even more.

The MPS is also stock and I replaced with a known good one. The result was no change in the lean popping problem.

This motor is dead stock no special valve springs and I dont run it past 5000rpm. The lean popping seems to happen under load only. If I rev the motor to 5000rpm no problem. Until I put it in gear and accelerate.

Now adjusting the MPS is something I have not consider. What can I do there.

Jeff I will read very carefully this test chart.

I really do appreciate the input. This is a very well informed BBS.

Thanks again everyone.

Chuckster

[Bleyseng]

Well for lean popping problems first look for vacuum leaks, everywhere! At decel the motor is pulling 15hg of vacuum so a leak could be it. Use starting fluid sparingly, spraying the injectors, plenum, hose connections, to find it.
As for leaning out a high rpms, is the MPS a 043 unit? IF it is try using a 037 MPS as they are set from the factory richer. Otherwise you have to adjust it which takes some special equipment (ie a Wavetek inductance meter) and a dyno.
If I remember right, the mix knob only is in effect when the tps is at idle. See Brad Anders site for more details on this.
WWW.members.Rennlist.com/PBanders
Geoff

[JeffBowlsby]

Hi Chuck, welcome to the real 914 place on the web...

If it were me I would suspect everything one more time before checking it off the list. Obviously something is awry and all it would take is one thing to couse your symptoms.

Go down the list on Brad Anders site.

Start with a full valve adjust, vacuum test, plugs, point ignition...

Verify that all your components are correct for your car (mismatching is common) and that each functions fully.

Its probably some little thing you have simply overlooked, but I tend to agree with Geoffs earlier wisdom...The MPS, the CHT resistor games...

I cant tell you how many 'known good' parts....Many are not. Even new, NOS and 'works on my friends car' parts...Check everything, its relaly not that hard if you are systematic.

[Chuckster]

I'm not too anxious to spend more money. And its a bit embarrassing that something as simple as a 914 is beating me. I must be missing something easy(better put something simple). As suggested by bowlsby could be a part that I have "assumed" is good and is not (IMG:style_emoticons/default/headbang.gif) .

The Test Chart that Jeff posted is going to be a check list. I will most definitely look very closely at the MPS & CHT.

The info I have gleened in 24hrs on this BBS has been more useful then all the info I have tried together in the last 2months.

Tomorrow is another weekend day and I can go over everything one more time. I will let you know if I find the problem. Thanks again for all the input. And Thanks again to Geoff for turning me on to this board.

Chuckster

[Brad Roberts]

"I have been a long time lurker at Rennlist but there is very little discussion on teeners"

Maybe I should go back to Rennlist and fire up some actual "914 related" questions....LOL (IMG:style_emoticons/default/finger.gif)

Welcome Chuckster (IMG:style_emoticons/default/clap56.gif)

I run a few ITA cars. We regulary have 100hp at the rear wheels and get spanked by all the Acura's. The best we could muster in this area is mid pack ITA. Which is about 3 seconds faster than the best ITB car (which is where we have been pushing to have the car moved into)

B