328 intermittent hesitation on acceleration

I have an 87 328 here in Brisbane Australia (euro I believe) which developed an intermittent problem which has now become permanent. I have searched through all of the forums for a similar problem without success.

About 6 months ago the engine started running rough after having stopped for a few minutes. After driving a few kms I stopped for a few minutes and on restarting everything was fine. Over the next few months the rough engine returned intermittently.

The intermittent symptoms were: drop in idle speed of about 100rpm (from 1000 to 900), engine miss and lack of power when accelerating. The engine miss was especially pronounced when cold, to the point that I would be concerned about pulling out across traffic in case the engine decided to leave me stranded in front of oncoming traffic. The problem would occur while stationary (idle speed increase and decrease) and while driving (perceptible drop in power while cruising and particularly when accelerating).

After a number of visits to the local Ferrari dealer (who is primarily Audi) and my usual mechanic (who is a second generation ferrari mechanic, especially older models) I have replaced the following – plugs, plug leads, extenders, injectors and have had all significant electrical terminals cleaned. Each time there has been a noticeable improvement in performance, but for whatever reason the intermittent problem was never fixed. I suspect the mechanic fixed what they thought was the problem, warming up the engine in the process, then took the car for a test drive and thought the performance acceptable.

Unfortunately as time wore on the intermittent problem became more permanent, so that I would only experience “correct” performance for random minutes each day. Towards the end it seemed that driving over a bump would cause the problem to disappear for a few minutes.

I suspect the mechanics thought I was imagining the intermittent improvement, but I had other people in the car and the improvement when the problem corrected itself was evident as faster acceleration, and was like turning on a turbo switch if the car was already accelerating.

As of today it seems that the part that was failing has failed completely, as the problem symptoms of missing on acceleration (esp when cold) and lack of power are now permanent. I have also tried wiggling and checking the connections to the Microplex ignition module as well as the K-Jetronic module without fault.

My question is - what part (or parts?) could fail intermittently and cause the symptoms of a decrease in idle speed, missing on acceleration (much more pronounced when cold) and lack of acceleration power?

Many thanks

 

Thanks for the feedback. The module on the right side is the K- Jetronic control module. I am taking my car back in to my mechanic next week for a regular service and an attempt to find this fault (again) and will mention the faulty relay to him. If still no luck I will probably take Martin's advice and look for a Bosch FI specialist.

 

Iain - do I need new gaskets when removing the distributor cap? I dont think am losing one whole bank as I have had that prroblem before with a faulty ignition module, and the problem is not as severe as that. Perhaps 1 cylinder is still playing up - I will get a timing light on the weekend and see if all cylinders fire the same. I will also start checking all vacuum hoses.

Zebra / Spirot - I have already wiggled the relay you mentioned without result, but perhaps it is totally dead now - maybe I can find another non-essentail 10A relay to swap it for to test.

When (if?) I find a solution I will post it here.

Thanks again to all who have responded.

 

For those who may have the same problem as me in the future, here is an update.

I checked all leads were basically operating by attaching a timing light to each lead and revving the engine. Inspected all vacuum leads - all appeared in good condition (looks like all were replaced in the last few years - I can't recall specifically changing them but usually replace at the first sign of wear) and sprayed some carb cleaner around likely air leak points without incident.

Went back to the K-Jetronic. Checking my VIN revealed that my car is US version Australia delivered (ie Lambda). Some research had shown me that the frequency valve should be buzzing when the engine was operating which it didnt seem to be doing. I could hear the relay clicking when advancing the throttle, but wasnt convinced it was operating correctly. I pulled the part and googled the part number - which lead to me another thread in this forum talking about the same part. Turns out the stock F part (which now costs $US500) is the same as a Porsche part (for ABS relay and which costs $US100). My part was the Porsche part. That thread gave some pointers on testing the voltages on the relay.

I determined I had a good live 12V on 1 pin (direct from battery), a good ground and 12V when engine running on a third pin, but no 12V on the output side. I shorted out the relay plug and could hear the frequency valve relay buzzing with the engine off - ie the frequency valve was probably ok. By this time the engine was warmed up and plugging/unplugging and shorting out the relay to force the frequency valve didnt seem to make much diffrence. I decided to leave it overnight and continue, as the rough idle and acceleration hesitation was worse when cold.

This morning I started the engine, shorted the relay, and the engine immediately increased about 100 rpm (the orignial "good" symptom) and accelaration seemed much smoother and instantantaneous - no hesitation. I unshorted and the "bad" symptoms returned. I couldnt believe I had appeared to have solved the problem! I tried this three more times to be sure.

So it seems the relay was defective, which fits the whole pattern I think. The relay would fail intermittently and the effect was on/off, not gradual - I assume due to something like deteriorating contacts in the relay. It also would make sense then that the deterioration would get worse over time. And as I understand it, if the frequency valve is not operating the air fuel mixture runs lean, which would cause a lower idle speed than if operating correctly, and would also cause hesitation esp. when cold and loss of power.

I have sent an email off to a few Porsche dealers to source a replacement. Fingers crossed I will have a new part in a week or two, and have solved a problem that I (and various mechanics) have been trying to solve for about a year. My only concern is that in the other case of a failed relay, the car wouldnt start, let alone run, whereas in my case the engine runs so so.

My other question is why a simple relay should cost $US500? Its bascially just a relay and diode right? And does the relay just function to provide power to the frequency valve when the engine is operating, or only powers the freq valve under certain conditions? Any insight would be useful.

regards

Greg

 

Postscript: I picked up a new relay from Porsche Brisbane today, fitted it on the spot, and was all smiles on the drive back (despite getting caught in the rain woth the top down). Excellent power and acceleration.

Steve - I agree that my mechanic probably tweaked the mixture with the FV not running. I recall him saying that he thought it was running lean (shame he didnt twig to the failed relay).

I must ad that this forum has proved to be an excellent resource - I have found all kinds of useful information, including how to deal with my fogged clock glass and non-lighting heater switches.

Also, thanks to Steve as it was his post to someone in Scotland a couple of years ago that got me on the track of correctly troubleshooting this issue (as well as zebra308)