Accessories degrade engine performance
 

The car is a 1973 1.7L 914-4. The car is stock except for oversized pistons and hydraulic lifters (added about 12 years ago).

I've taken the car to 5 different shops, all of which couldn't find the source of the problem, or decided not to work on the car after having in their possession for a while (the local Porsche dealer was the latter).


The car seems to run fine without any accessories (e.g. lights, heater, outside air blower, etc). However, turn any of these items on, and the performance degrades immediately. The engine begins to miss and pop. Engine RPMs drop about 1000. The engine seems to lose lots of horsepower. Turn off the accessories, and normal performance is restored. I haven't been able to notice the affect with JUST the turn signals on, however, the turn signals blink faster than normal with accessories on. The more accessories I turn on, the faster the turn signals blink.

I first noticed this problem 2 years ago. The problem seems electrical in nature to me. It's also not as severe on humid days. I don't have any extra accessories in the car (like cell phone, CB, fancy stereo, etc). I recently swapped out the relay board, relays, voltage regulator and alternator with no noticeable affect. The battery cables are new also.

The problem is most noticeable when I try to hold a constant speed. If I pump the gas pedal, the probem doesn't seem to exist while I'm pumping the gas pedal (but that doesn't make for a very smooth or economical ride, not to mention that my foot gets tired quickly...).

Any suggestions on where I might begin to look for a problem?

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Considering the harnesses common junction is the relay board, I'd check that. Fuel injection harness conection, Fuel pump connection, alt.connection. If things are better when it's humid this sounds like a logical place to look.

You might also just check the grounding of your cars complete system. Ground is common to everything... Ive heard of lots of problems with these cars just due to loose or corroded ground straps and such. just a thought.

I'm with G5 on this one, the electrical system needs a complete circut to work. There are 6 grounds on a 914: one behind each headlight (front turn signals and headlights), one under the dash (main relay baord, dash), one under the relay board (tail lights, relay board, I believe the fuel pump, and the VR. Can tend to rust out, make sure the metal is sound), the "major headache" trans to body ground. Most commonly the problem. One from the battery to the body. If the car were a 75-76 it also has one under the tank for the fuel pump.

Check that the trans ground is in good shape, also the battery to body. All the 914's I've seen have a ground wire added between the Volt Regulator and the ground under the relay board, worth a try? The F.I. is grounded to the engine block under the air intake. It is a three terminal spade connector that goes through a case bolt.

Look at these articles http://www.pelicanparts.com/techarticles/914_alternator_troubleshoot/914_alternator_troubleshoot.htm

and

http://www.pelicanparts.com/techarticles/mult_starter_diag/mult_starter_diag.htm

Sounds silly but start with the simple things first, i.e. test the battery, then test the cables, then the grounds through the frame, then the components...

BTW I've had a few "dead" shorts to ground, what happened to me was the car died and the red alt light was the only thing that worked (then there was the smoke...) it 'could' be one of your acc circuts is making a partial short. Do any of the wires get hot?

Sounds like a weak alternator and possible a battery getting old to me. I'd recommend pulling the alt and having it checked by a good elec shop see what they say. We have several in the San Diego that will check them while you watch to see if they are any good and for 000$ too. I noticed on our street 914 when the headlights were on the voltage would drop to about 11.5 to 12.0 volts, with no lights the voltage was 12.5 to 13.0 volts and a few months ago the alt just quit working? I put in a rebuilt one and the voltage stays the same now. Good luck.

[This message has been edited by john rogers (edited 01-31-2000).]

In general, a check of the voltage across the battery terminals is enough to start the diagnosis on the charging system. Remember that the center-console voltmeter is there mostly for laughs, and is not a good indication of the health of the charging system.

The original problem sounds like bad connections to me. All of the connections should be checked. All of the grounds, and the "hot" leads. The battery terminals, and the extra wires that go on the (+) terminal. Plus the ignition switch. The current that runs all of the lights etc. goes through the ignition switch. So does the current that goes to the coil. So a voltage drop across the switch may cause these type of problems. Also fuse #8 or #9 (forget which one). Clean up the fuse holders, replace the fuse. Heck, do that on all of the fuses, including the two on the relay board. Fuses are cheap...

Good luck!

--DD

Ok, so is it safe to say that the voltage should not drop when the headlights are on? I though this was prob "normal" given the technology... Ya think I'll be looken at a new alternator soon? Thanks all

The voltage *at the battery* should not sag too much. It should not go below 12.6V when the engine is at 2000 RPM or more. The voltage gauge in the dash can go down to 8V or less even when the car is healthy.

It's probably some sort of dirty, pitted, or corroded connection.

--DD

The car is FIXED!

Corroded connections it is - I actually had 7 volts at the coil. I'm quite impressed that the car ran as well as it did! Anyway, I cleaned these connections, and voila! The car is back to normal. I also gained another 0.5 volt by cleaning the battery ground (at the car side).

I'm extremely disappointed that the shops I took the car to didn't discover the cause of this problem. I'm no mechanic, but with the advice of this technical forum and some reading in a Haynes 914 manual, I was able to troubleshoot and fix the problem. Perhaps they are more thieves than auto mechanics. Then again, if you want something done right...

Thanks again to all who offered advice and experiences.

Glad to hear it's running happily again! It's nice to know when that happens.

--DD