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Discussion Starter #1 (Edited)
I'm a complete newbie, having owned a terrific 2 liter TS converted '75 Bertone for six months, and hope somebody's able to help me out.

Driving hard at a trackday last saturday it started briefly (max. ½ second) cutting out (no fuel/ignition?), then immediately returning to full power afterwards. It did it at the three exact same spots on the track in third gear, app. 4500 RPM, under full power, lap after lap. I also noticed a couple of times that the rev counter dropped from the 4500 RPM to zero, then quickly returning back again (this didn't happen every time though).

Anybody got a suggestion as to what might be causing this problem? (and is this posted in the correct place?)

Best regards

Nikolaj
 

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What do you mean by "rev limiter drops to zero" ? Or do you mean "rev counter drops to zero"? Rev counter drops to zero usually means that the coil doesn´t get any signal (and so there´s no spark) if the rev counter is connected to the coil.

What kind of ignition do you have? Stock motronic or something different?

Check all cables between ECU and ignition module and also between ignition module and coil(s), it´s a sign for e.g. a rubbed through cable that causes a short-circuit in just a particular situation.

My car e.g. had some strange behaviour just in left bends until i found a damaged cable that touched the engine just in left bends and so caused a short-cirquit.

Thomas
 

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Discussion Starter #3
Hi Thomas

Thanks for a quick answer. I meant rev counter (now corrected). Ignition I'm not sure, but i think it is stock Bosch Motronic.

I'll check cables tonight.

Thans again.
 

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I have the same thing happening to me on a s3 spider engine, i changed the module , some guys here suggested the switch (next to check) but i too feel that in my case also the thing happens because of a short.
 

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Discussion Starter #5
I changed a couple of old connections/wiring in the engine bay, tightened whatever was loose and went for a drive. It took 15 min of very hard driving before it happened again. It only happens under full power (gas pedal completely pressed) and revs 3500-4500 - and as said before, not that often. I am pretty clueless and will probably have to get it to a qualified mechanic and pray it's not a 10 hour search job...
 

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Still sounds like an intermittant contact somewhere.

Electric fuel pump(s) fuse and/or relay OK?

Connectors on said pumps proper if electric?

Motronic harness plug clean, securely mounted and no chafed wires where it passes through/around edges of things?

Good solid grounding strap and wires on engine, particularly as the Motronic grounds up there? (typically on the cam cover if it's L-jet Motronic)


The 'exact same spot' is what's causing me to think connection/short.

Conditions just happen to be perfect in that area, and it took you 15 minutes to reproduce it out on the road. (depending on comparative road to the spot on the track, you might have been lucky to get it to happen at all)

I suppose it's viable that the ignition is going too far advanced, (Motronic ignition is 'fixed' or 'dumb' with the ICU controlling the advance and retard, not the distributor) though that wouldn't explain why the tach drops off. (but a half cooked coil or bad connection would)

Just kinda reaching here.........
 

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Discussion Starter #7
Thanks for your input Tifosi. Very insightful.

To clarify my test on road didn't reproduce the tach drop - only the brief cut outs. The tacho drops actually only happened a handful of times on the track.

I'm having a bit of trouble with some of the terms that you are using (I'm Danish) but I am already suspect the grounding strap (if its a approx. 3 mm. wide strap connecting the side of the engine and chassis). The rubber engine mounts are bit worn (waiting for replacements to arrive) and the engine does rock/tilt too much when revved... I will definitely be in the garage tomorrow running through your list.

Thanks again!
 

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Driving hard at a trackday last saturday it started briefly (max. ½ second) cutting out (no fuel/ignition?), then immediately returning to full power afterwards. It did it at the three exact same spots on the track in third gear, app. 4500 RPM, under full power, lap after lap. I also noticed a couple of times that the rev counter dropped from the 4500 RPM to zero, then quickly returning back again (this didn't happen every time though).
Hello, Nikolajk,

I don't know much about TS motors because they are not common here in the states. However, what you are describing sounds like a common ignition problem. As others have noted, the first things (and the easiest) to check are your electrical connectiions---all of them. When we speak of "grounds" we are referring the "earth" connections.

The cutting out you mentioned sounds to me like bad connections. These can be at the electrical/component connection itself or at the ground/earth for the entire circuit. Check and clean everything.

The cutting out under heavy engine load also sounds like an electrical connection or ground problem. That would be my first guess. However, the problem could also be caused by broken/cracked wires or connectors which are occasionally shorting or arcing under load.

Before you move to the next step in your diagnosis, you must insure that all the connections and grounds are OK. While you are at it, I'd also suggest that you also remove and reseat the fuel pump relays, all the fuses, and the ground/earth connection for the fuel pump. Hopefully, after you do this, the car will start and run just fine.

Curiously, I just went through this same exercise with my wife's truck (this is Texas, after all, and women like trucks here :) ) My "ignition" problem truned out to be a corrorded fuel pump relay.

If the cutting out persists, however, then you have to consider more serious problems. First check the coil/s. A failing coil will break down under load. Check the TS specific wiring---all of it---for obvious breaks, splices, taped repairs, etc. Check also for repaired connectors, loose connectors, etc, along with the spark plug wires, and distributor cap/s and anything else you can think of that might fail or corrode.

Alas, I know nothing about motronic systems but, since they are modern, I would presume that the one on your car has a diagnostic port. Even though your motor is in a 105 car, it's still basically a TS/75 motor so an Alfa diagnostic tool (assuming they exist) ought work just as well on your car as on a 75. The tool, of course, will check the integrety of the motronic components. It may even have specific codes to help diagnose what happens to the car under load. I would think that most of the Alfa specialists in your part of the world would have such diagnostic tools.

It would obviously be very helpful if you could contact the person who did the actual engine conversioin. Basically, you have a car whose engine was pulled (perhaps rather roughly) from an Alfa 75, sold to someone who transplanted it into your car, and then sold the car on to you. Lots of different hands have been on this motor. It would surely be useful to be able to talk to the guy who did the transplant.

I apologize for all the verbiage. I am not succinct. :) Good luck with your car.
 

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Hej Nikolaj.

In what way are the ignition modules/amplifiers mounted? on the 75 TS there is a body bracket that holds the amplifiers and coils, I doubt that it was moved to the Bertone?
The ignition modules needs a very good ground from it's holes/casing to body and they get seriously hot when in use so unless they are bolted directly to body I suggest you do that as a first step and see if that fix the problem.

Is that picture from Knutstorp by the way? Looks sharp!
 

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Nikolajk,

If you are still having the problem, I recommend you double check your timing on both distributors.

I had a similar issue but I was loosing power around 3500 rpms. the only way i would avoid it was to go full throttle past the 3500 rpms and was safe until I reached 3500 rpms either on the way up or down.

somehow the timing was a little off and one was cancelling the other out.

you can probably find details on how to double check your timing on craigs manuals site: http://www.users.on.net/~craigf/
 
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