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Discussion Starter #1
I have a '91 164S that has started to run really rough lately. I'm afraid I've been doing too many home improvement projects lately and my automotive diagnostic skills have gotten a bit rusty. If anyone has any suggestions as to what to test I would be very appreciative.


I'm not sure which facts are relevant, so here goes...

1) 6-8 weeks ago my car started to have a slight stumble at idle. This happened several years ago and replacing the plugs corrected it. I looked at the plugs, but they were not very old and looked very good so I didn't replace them. Just checked the gaps and reinstalled and everything seemed fine for a while.

2) A couple weeks ago the weather started to get colder than normal and when started from cold the engine would run really rough, smelled very rich and missed like it wasn't firing on all cylinders. After a minute or so it would smooth out and be fine. If I gently revved the engine to ~2000 rpm for a couple seconds that also seemed to help. It didn't always run rough when cold, but this has became more frequent.

3) It usually only happens on a cold engine, but last week it ran fine when cold, I drove it a few miles and parked it for 15 minutes. When I went to restart it the rough idle reoccurred then went away after a minute or two. After this point, when the idle is rough pressing the accelerator pedal has no effect -- no change in rpm. Once the idle smoothed out everything was fine again.

4) Last Thursday I went to start it from cold and the rough idle never improved. It ran very poorly for a minute or two and then died. While it was running I tried pulling a plug wire and it didn't have any effect (either good or bad). Feels like it is running on 3 cylinders and the exhaust smells very rich.

5) I tried restarting the car this weekend and it started right up and idled nicely, but after several minutes the idle got rougher and began to miss and eventually stalled. I checked one of the plugs and it was dry and very sooty compared to a few weeks ago.


I checked the codes and the ecu puts out 1-2-2-3. I tested the coolant temp sensor (ok) and the throttle position sensor (ok, but readings seem reversed from manual -- idle and WOT pins reversed. I'm assuming the manual is wrong) and inspected the black rubber tube between the afm and the throttle (ok). The afm moves freely, but I can't find details on how to test it. My manual doesn't have many details and only seems to cover the afm used on the base and L models. I didn't test them, but have in the past couple years/10k miles replaced the plugs, cap, rotor, spark plug wires, coil and fuel injectors.

Does anyone have any suggestions for what else I should check or know the proper way to test the 164S AFM?


thanks,
-Obie
Tacoma, WA
 

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I would start with inspection inside distributor cap for cracks, corrosion, condition of carbon button, rotor condtion/resistance of 1.1 kohm.

Next measure resistance of each plug wire for reading near 2.5 kohm and coil wire for 1 kohm.

Check coil tower for corrosion.

What kind of plugs are you running?
 

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Discussion Starter #3
Thanks for the suggestions. I'll check them out.

The plugs are Autolite Iridium, iirc. I think I have an extra set of plugs hanging around so I might swap them out just to see if that changes anything.

-Obie
 

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A while back I had some pretty serious missing and stumbling on a cold 164s engine. It was completely eliminated by replacing all the oem clamps to those small tubes that connect to the intact hose (hmm.. how many, I guess 8) with Wurth 19-28mm clamps. You'd be surprised how these minute leaks can confuse the air flow meter.
 

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I am afraid what you have is a bad Fuel Regulator.
The Diaphram in the Regulator is puntured and this is causing raw fuel to be sucked into the Intake Plenum ( and thus into the cylinders ) via the vacuum hose. I recently had a similar problem with my S, corrected with a new Regulator.

Howard.
 

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You can check for ruputured fuel regulator by removing small vacumn hose going to it and see if you get any fuel out that vac port.
 

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A ruptured fuel regulator diaphram is certainly a possibility, but when I had this problem with a Volvo 740 turbo, the car ran roughly all the time, while Obie's car seems to runs fine at times and crappy other times, mostly when it's cold.
 

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Usually some kind of a bad connection or wire at a sensor, injector, air flow meter or in ignition system can be worse when cold and if moisture present.

Go through connections and clean with contact cleaner and grease them up with dielectric grease.

Rule out weak spark by inspecting coil tower for corrosion and inside dizzy cap for worn out carbon button, etc., too.
 

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I will stand by my comment that the Fuel Regulator is bad. The Diaphram will only leak when subjected to a vacuum. Starting the car with the vacuum hose disconnected will do nothing.
Obie, although you did not mention it, I am willing to bet that you are suffering from poor fuel milage. This is another side effect of a punctured Fuel Regulator diaphram.

When I had the problem with my S it was intermittent, some days it would do it some days it won't. The times it did I would have to crank it a long time before it finally started, belching a big cloud of black smoke out the tail pipe. It would idle irratically for a while ( comparable to running on 4 cylinders ) before smoothing out.
I finally diagnosed the problem to be fuel related after one day sitting in a South Florida traffic jam and have it cut off repeatedly. The only way I could keep it running was to keep the RPM's up to clean the plugs which were loading up.

Thanks, Howard.
 

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OK, then let's test Fuel Pressure Regulator with engine running by using a Mighty-Vac hand pump with its clear bottle and tubing hooked to vac port on regulator. Start up engine and then pump M-V hand pump and see if you can suck any gasoline into bottle.
 

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Discussion Starter #11
Thanks everyone for all of their suggestions. I finally had a chance to start checking some of these out.

1) distributor cap is good although there was a small bit of condensation inside the cap.

2) plug wires are good and all have the same amount of resistance.

3) With the engine off I tried connecting a mighty-vac to the fuel pressure regulator vacuum line, but didn't get any fuel out of it. I'll try this again later with the engine running.

One thing I did find was that the rotor is horrible! If you can't tell from the angle, the little bit of resin near the tip of the rotor has melted or burned up. The resistance is around 200K ohms which I believe is a wee bit higher than it should be. This rotor was not that old, so I'm not sure if it was defective or if this occurred as a result of something else. Last summer I replaced the original coil with a spare higher performance one I had laying around just because. I wish I had looked at the rotor then.

I'll pick up a new rotor this weekend and report back .

thanks,
-Obie
 

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Thanks everyone for all of their suggestions. I finally had a chance to start checking some of these out.

1) distributor cap is good although there was a small bit of condensation inside the cap.

2) plug wires are good and all have the same amount of resistance.

3) With the engine off I tried connecting a mighty-vac to the fuel pressure regulator vacuum line, but didn't get any fuel out of it. I'll try this again later with the engine running.

One thing I did find was that the rotor is horrible! If you can't tell from the angle, the little bit of resin near the tip of the rotor has melted or burned up. The resistance is around 200K ohms which I believe is a wee bit higher than it should be. This rotor was not that old, so I'm not sure if it was defective or if this occurred as a result of something else. Last summer I replaced the original coil with a spare higher performance one I had laying around just because. I wish I had looked at the rotor then.

I'll pick up a new rotor this weekend and report back .

thanks,
-Obie
I did not think FPR would have been a problem here. Air leak or Electrical was my thoughts. Lets see how it goes with a new one!
Ciao!
 

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Thanks everyone for all of their suggestions. I finally had a chance to start checking some of these out.

One thing I did find was that the rotor is horrible! If you can't tell from the angle, the little bit of resin near the tip of the rotor has melted or burned up. The resistance is around 200K ohms which I believe is a wee bit higher than it should be. This rotor was not that old, so I'm not sure if it was defective or if this occurred as a result of something else. Last summer I replaced the original coil with a spare higher performance one I had laying around just because. I wish I had looked at the rotor then.

I'll pick up a new rotor this weekend and report back .

thanks,
-Obie
That is a nasty looking rotor. Rotor resistance is supposed to be 1.1k ohm aka 1100 ohms so 200 ohms is not high resistance but low. Maybe your racer boy coil not such a good idea considering how burnt that rotor tip is.
 

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That is a nasty looking rotor. Rotor resistance is supposed to be 1.1k ohm aka 1100 ohms so 200 ohms is not high resistance but low. Maybe your racer boy coil not such a good idea considering how burnt that rotor tip is.
But 200K ohms as Obie said is much too high.

Last time I had a rotor that looked like that (on a different engine), it was the cause of the problem - so, here's hoping that the culprit is found.

I go along with your comment that high-performance coil is really not such a great idea when the coil is driven directly from the ECU (I wouldn't risk any change for fear of overloading the output transistors). Also, Bosch would surely know what they are doing when designing an ignition system, I bet that coil is about as good as possible for the distributor-system type. (When finding a Lucas coil fitted to an old FIAT, that's a different story...)

After recent experience with occasional rough running/cutting out being caused solely by plug leads, I think you can never be too careful with the basic things.

I'm tempted by those silicone hoses in another thread since I suspect my engine getting extra air on one or two cylinders with perished couplers.

-Alex
 

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I would put an OEM coil back on it and buy a genuine Bosch rotor and dist. cap. That one is not made by Bosch. I'm getting 1253 ohms on a new Bosch rotor I have sitting here measured on a Fluke 73.
Charles
 

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I hope this doesn't derail this, but what sort of "performance" coil did you install? Will a Bosch "blue sport" coil work in these cars, or is that a bad idea?
 

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Discussion Starter #17
The coil I installed was a Crane Cams PS91 that I had sitting around. The OEM coil worked when I took it out; I just thought the PS91 might be an improvement. In hindsight I wish I had checked the distributor rotor at that time to see if it was okay, because I really have no way of knowing if it failed as a result of the new coil or if it was already on its way out.

I ended up replacing the failed rotor last weekend with a BWD brand unit from a local auto parts place. It was half the price of the Bosch part, came with a lifetime guarantee and measures in at a nice 1,023 ohms. The car runs great now and I've decided to leave the new coil in place for the time being. I'll check the system again in a month or two to see if anything has changed (resistance-wise).

I want to thank everyone for their suggestions. Without them I would probably still be outside trying to figure out the problem.

-Obie
Tacoma, Wa.
assorted Alfas
 

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If anything, keep in mind that parts for our cars can be a bit scarce. As was mentioned, the new coil might just have too much resistance for the primary voltage supply.

Also, control the width of the gaps on the spark plug electrodes. A high voltage will erode the contacts faster, causing the coil to have to supply more voltage to bridge the gap, thus, rotor tips and carbon contacts on the distributor cap burn faster.

Have you considered fitting plugs with triple electrodes? Before the coil on my car was replaced, the only plugs that kept it running without misfires were a set of Mercedes plugs with three electrodes.
 
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