Martin, I can answer all your questions but first thought I’d give a current update with answers to some of your questions.
Over the last two weeks I’ve checked many things and have now managed to start and run the engine several times just as it used to run. So, good news except that I’m not sure I’ve answered all my own questions about the root cause of the original problem.
When the driver of the recovery truck first arrived we pulled all the plug leads and as I cranked the engine from the ignition key he checked for sparks at the plug leads. He said there weren’t any, which I’ve no reason to doubt, but it would have been nice to actually see that and at which leads because he possibly just looked at the first one. I carry a new distributor cap and this was fitted and we then had sparks. Because I was not at the engine again I don’t know from which lead, or leads, the spark came. In hindsight this wasn’t a conclusive test to show that both cylinder banks were sparking due to the dual arrangement of this distributor (2 coils and 2 king leads). It may have been sparking on one bank only. In moments like this you, or me at least, can forget to approach the problem in a logical fashion and risk loosing some of the evidence. Anyway, a start was attempted but without success. Maybe the engine was flooded by then.
Once the car was back home, on cranking using my remote starter leads, there were sparks at leads 3 and 6 so the ignition system appeared to be good. The plugs were then removed, so to answer one of your questions.
MFaulks wrote:.Spark plug, that doesn't sound right, can you post a picture of the offending plug, and some of the other plugs too please?
Unfortunately I didn’t make a note of which plug came from which cylinder but I know that the number 5 plug is the one in the middle of this photo.
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It’s not as it came out as I cleaned some of the deposit that was bridging the electrodes and scraped most of the deposit off the end face. The plugs were champion RBN9Y by the way. The other two plugs in that photo I’m pretty sure are 4 & 6 because I did make a note that 1, 2 & 3 looked a bit orange as this photo shows. These plugs had been in the engine since its first start up 2 years ago, since when the car has covered about 1200 miles.
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The compression tests were then done that showed cylinders 5 and 6 with low readings. To answer another of your questions.
MFaulks wrote:.You say it holds 60 and 90 psi, that is still holding a bit of pressure, so the gasket hasn't extruded, otherwise it wouldn't hold that even.. if your valves are slightly stuck open you will also have low cylinder pressure... does the gauge hold up after you stop cranking, or does it just fall rapidly to zero pressure?
My gauge has Schrader valves that hold the pressure reading in the test hose and gauge whilst you make a note of the reading and then you release the pressure to check the next cylinder by pressing the plunger below the gauge, as in the photo. In fact, you can remove the hose and gauge completely from the cylinder and the gauge will still hold the pressure reading until you press the plunger.
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I understand where you’re coming from but I assumed that the testers were all like that otherwise as soon as you stop cranking the engine, the pressure would drop to zero unless the engine stopped rotating with both the inlet and exhaust valves closed, i.e. in the region of TDC on the firing stroke for the cylinder under test. To test that theory I repeated the compression test on one cylinder but held the tester plunger in whilst the engine cranked. As soon as the engine stopped the pressure fell to zero. Cranking as normal held the pressure at the gauge.
Two more of your questions.
MFaulks wrote:.5& 6 are the hottest cylinders with your hardware config, could you have potentially been getting knock?
At the end of March this year, about 170 miles ago, I fitted a Lumenition Optronic electronic ignition system to the car. The system is the only one I found that has the twin infrared sensor unit for fitting in this distributor. I fitted it to give, hopefully, a more reliable and maintenance free system. The existing coils and ballast resistors are being used.
After the electronic system was installed the timing was set to the previous Alpine MDR setting of 10 degrees BTDC but I found that, when running it with the car static, it was backfiring on the overun after blipping the throttle, more than I remember it doing previously when on contact breakers.
Increasing the advance reduced the backfiring and increased manifold vacuum which, I’ve always been lead to believe, was the way to go for better running. A few test runs were done on the road and on one occasion I thought I heard some pinking at low speed, in third gear, under acceleration. After this run I checked the advance statically and it was about 18 degrees BTDC. As a compromise, the static advance was then reset at 12 degrees BTDC and no further pinking has been heard.
When the incident happened my first thought was that something may have failed in the electronic system, as this has been the only significant change made to the car and it was a recent change. It was only the low compression readings that threw up other possibilities.
MFaulks wrote:.What ignition timing have you got dialed in? ?
When on contact breakers the static timing was set at 11 degrees BTDC. As above, with the electronic system, 12 degrees BTDC. I now notice in the GTA manual that the setting for the GTA carburetor car is 15 degrees BTDC +/- 1 degree. With the GTA cams and followers fitted to my engine maybe it should be set to this value also?
Back to the checks I’ve been making.
Lumenition literature gives information on several electrical tests that can be done, using a multimeter, to check the optical units and power modules. All these tests checked out as the literature prescribed. I then checked for sparks at all the plug leads and there were none at 4, 5 and 6. This check was repeated several times with the same result and also with a different distributor cap. In the last week I bought 2 NOS rotor arms on Ebay and with one of these fitted all plugs sparked with either distributor cap. It therefore appeared to be a problem with the originally fitted rotor arm. However, looking carefully at this rotor arm doesn’t reveal any signs of failure or tracking marks.
I thought it was worth attempting a start at that stage, and it fired and ran straight away. I had also bought a new set of NGK BPR6EFS plugs which were fitted before the start was attempted. Just fancied trying something different to Champion. It ran it for about 20 minutes and beyond the point where the radiator fans start to cut in. On the assumption that the oil squirted into the cylinders when previously doing the compression tests, would have now cleared, some further readings were taken. Cylinder 5 attained 140 psig, more than double the post-incident reading. Cylinder 6 has an even higher reading.
I don’t have an explanation for this. When I did the first test the battery was beginning to struggle, so might have influenced the readings.
At the moment it looks as if the original rotor arm was suspect, I’ll see what further outings bring.
Martin, one of your other questions, I’ll answer all the others if you want. Just let me know.
MFaulks wrote:.Plus, what gas were you running, 95 or 98?
Usually 95, the last tank full was Tesco unleaded which I think is 95. I’ve been regularly adding Millers VSPe Power Plus Multishot (Ethanol / Lead / Octane) fuel treatment as a precaution as I’m not sure whether the valve seats are suitable for unleaded.
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1970 A110V85 and 1980 A310V6.
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