164 TS hesitating during acceleration

Hi all,

My '92 164 Twin Spark is experiencing a serious loss of power/misfire under acceleration, especially between 2-3000rpm. I changed the spark plugs last night (the old ones were sooty, suggesting rich running) and it still does it.

The engine also seems to stumble during idle. It runs OK for a few seconds then revs drop for a second or two, then so on and on.

There doesn't seem to be any obvious leaks in the intake/vacuum hoses. Does anyone have any suggestions?

Thanks.

If its running rich air filter, coolant temperature sensor, AFM or idle mixture adjustment. Are distributors clean with carbon brushes free, are both sets of spark plugs firing? Are you certain that the rubber boot connecting the AFM to the throttle body isn't cracked or leaking?

Thanks, I'll look into it. To test each set of spark plugs, is it just a case of disconnecting each coil in turn?

My suspicion is that it's air intake-related: either the VAF sensor or the rubber boot, as you say. I've changed the air filter in the last week so I don't believe that's the problem.

Not sure about exactly where to disconnect each coil. I just sit 4 spare plugs on the cylinder head and connect the the plug leads from each distributor in turn. That way the engine runs on 4 plugs and you see the 4 on the head firing which shows that the leads are OK.
To test the AFM stick a pencil in from the air filter end and check that the flap is moving freely and smoothly. You can connect an ohm meter between terminals 2 and 3 on the AFM and it should show an increasing reading as the flap opens but note that it goes in steps. The terminals are numbered from the end next to the idle mixture adjusting screw.
For air leaks the rubber boot is favourite. Other possibilities are the seal where the idle speed controller fits into the inlet manifold and the brake servo and its associated connecting hose.

i have posted almost the same problem with my 3.0 166, although i have have no miss fire! however i did on my 164!

The air flow sensor, disconect and clean out with WD40 - it worked a treat.

just leave it to dry and put back into place.

Good luck, it post back your results as i wanna find out whats up with my 166 as i still have not had chance to get to that one yet!

I might have a pop at it this evening. I'll let you know how I get on.

Originally Posted by a17esh

i have posted almost the same problem with my 3.0 166, although i have have no miss fire! however i did on my 164!

The air flow sensor, disconect and clean out with WD40 - it worked a treat.

just leave it to dry and put back into place.

Good luck, it post back your results as i wanna find out whats up with my 166 as i still have not had chance to get to that one yet!

I think this might be what my 3.0 166 is doing too - sounds very familiar. Was there a warning light on the dash illuminated which looks a little like a torch shape with little lines going in and out of it?

Being not mechanically minded at all, can you give me a run down, in layman's terms as to how to find, disconnect and clean out this airflow sensor?

Cheers

Keith

Well, I checked the rubber gaiter: I actually took it out entirely and stretched it. No splits or holes in that. All of the pipes adjoining it seemed secure and split-free. The idle control actuator was a nice fit into the plenum and the seal was in top condition.

The VAF sensor opened nice and smoothly but the resistance between pins 2 & 3 did some funny things. It was about 380 ohms when closed, rising rapidly to about 1.1kohms at about 10% open, then falling slowly off until it reached 380 ohms again at fully-open. Is this normal? From what ak164 is saying, it isn't.

One alarming finding was that most of the intake system after the VAF sensor seemed to be coated with a varnish of old oil. The oil vapour separator and its pipework looked as though they had been filled with axle grease. I flushed it all out with solvent but I'm still getting the hesitation.

Will try the electrical system tomorrow but my suspicion is still the VAF sensor with its dodgy resistance readings. Any comments?

PS: I could be wrong but I think you guys with the 166s might have a Mass Air Flow sensor instead.

Originally Posted by carliterature

Being not mechanically minded at all, can you give me a run down, in layman's terms as to how to find, disconnect and clean out this airflow sensor?

Cheers

Keith

Keith, I think you may have a Mass Air Flow sensor but it should be in the same place. The air flow sensor on my 164 is shown on the right of the picture. It's the thing with the black square on top. It goes between the air filter and the throttle and is used by the engine management to measure the air getting into the engine.

Mine is basically a tube with a spring-loaded flap inside it that deflects according to the airflow. The flap moves a potentiometer (variable resistor), in turn, which provides the feedback to the management ECU. I think yours will work slightly differently but it achieves the same result.

To remove it, simply undo all of the hose clips and electrical connections (remembering where each one goes!). Clean it out with some solvent and, as they say in the Haynes manual "refitting is the reverse of removal"

I have just checked the afm resistance readings on my 164. My readings are substantially the same as yours, ie 370 closed rising steadily but rapidly to 1070, holding around 700 to 800 before falling back to 600 fully open.
My guess is that your afm is OK.
The "gunged up" separator is not uncommon it results as you found in deposits on the intake after the afm, it often causes irregular running at low throttle due to deposits around the throttle butterfly. You should check the small drain pipe from the bottom of the separator to the crankcase, it blocks where it enters the crankcase and results in the separated oil passing to the intake. Just disconnect it at the separator and blow through it to check it is clear.
I have just looked at your nice thumbnail pic. It occurs to me that the distributor shown is wrongly positioned. The outlet for the HT leads should be approximately horizontal and not pointing upwards. This has no effect on the timing, but it does mean that the spark is jumping a gap from the rotor arm to the HT contact, which results in burning of the contact.

You should get rid of it Nikos, those Italian cars are hellish unreliable... And to think you sniped me on that POS!

Now where did I put that slave cylinder????????

Originally Posted by team piston broke

You should get rid of it Nikos, those Italian cars are hellish unreliable... And to think you sniped me on that POS!

Now where did I put that slave cylinder????????

Yeah, cheers Rob. We'll be ready for Santa Pod!

For the benefit of other forum members, Rob and I are both entering 164s in the Staples2Naples banger rally this September. As you can imagine, there is a bit of friendly rivalry between us. For more information, go to www.staples2naples.com

Back to the subject at hand, the finger of blame is now pointing to the Engine Coolant Temperature sensor. However, trying to get me Alfa main dealer's parts department to send me the right one is proving more difficult than it should be.

To be fair to them, the Alfa parts CD shows numerous sensors, some listed as both for coolant temp and oil pressure. It simply refers to them all as 'senders', without giving any idea as to what their specific function is.

The most likely culprit so far is the one to the rear of the engine, at the flywheel end. It is quite a bit bigger than the others and has a yellow plastic shroud over the spade terminal. Does anyone know if this is the right one?

i went to santa pod!!!!!!!! Not bad was it! That Jet engine! WWWOOOOW!!!!!! That was just stupid!

I cant confirm the part number for the TS but it is important you get ECU coolant temp sensor not the standard engine coolant temp sensor. They normally dont have a spade terminal but a F1 type fitting, you can confirm which one it is because if you unplug it whilst the engine is running it will probably stall, or try to start car with it unplugged. I would have put the ecu coolant sensor at top of list as well so I think you are on right track.

Can't believe the dealer not knowing. Ask to speak to a mechanic there that has worked on a 8v TS engine, they will know.

Good luck.;

Yeah the dealer already tried to flog me the two sensors which go in the end of engine block but these are for the temperature gauge and the overheating warning light. I specifically asked for the one for the ECU but obviously I wasn't clear enough.

All the sensors on my engine block seem to have spade terminals. Only the external stuff (VAF meter, throttle switch, Idle Control Valve, ignition amplifiers) seem to have 'proper' connectors but then those are made by Bosch. I'll try unplugging it and see what happens.

I even went to the extent of buying a Haynes manual for the Citoen BX off eBay as the 1.9 GTi has the same Motronic ML4.1 management system. Guess what? It says "please refer to a qualified mechanic with the appropriate diagnostic equipment". As if!

The CTS is at the back of the block at the clutch end. It is just visible looking down between the inlet manifold and the head. It has two terminals is a Bosch part with a plug the same as the ISPC and is listed as part of the Fuel Injection system. It should read around 350 ohms on a hot engine and 2.5k ohms at 20 C. It is the same injection system as the Citroen BX GTi 16V.