Engine Games Part 5 - The search for Spark
So Oct 2 we have everything connected that's necessary for 'Main Engine Start'. Cranking it over with no feed to the coil shows oil pressure building, and there is now fuel flowing freely from the outlet from the fuel filter. Static timing set at 5 deg ATDC using the mark on the distributor as there is a Pertronix unit in the distributor. Seems to line up as it should - this is a later photo after I re-installed points, but the positioning was the same.
Petrol can be smelt down the stacks and squeezing the cold start piping gives a liquid 'squishing' sound down the stacks .... but she no want to go .... not even a desultory cough or fart. Some elementary diagnostics show a reasonable spark output from the coil (holding the outlet cable 4mm from the fan housing), but nothing or very weak sparks on each cable to the plugs. I had at that time only one of those devices that you plug in between the spark plug and the cable - which is not a lot of use in a Porsche as it's down the hole, and laying the plug in contact with the engine case gave erratic, weak and inconsistent results. More technology called for. Onto ebay for one of these - less than £10 inc p&p complete with instructions.
Measures the strength of the electrical impulse in the cable.
Before it arrived it was time for a trip to Germany - to the 'famous' Veterama Autojumble in Mannheim. Another DDK'er who shall remain nameless (Dave O'Connor, or stretch on here) went there a few years ago and reported stalls thigh deep in cheap rare early Porsche parts - when he was looking for Merc parts. 'Got to be worth a trip lads' - be a nice boys outing. So Garry, me and he head off ....
First to the Porsche museum
Then to collect some seats for Dave, and to Veterama. Below you can see photos of all the magnificent Porsche treasure we found
Not a f**king thing. There's more Porsche parts in my mothers garage. There was one smart-arse Italian Porsche racing 'expert' with a few goodies at exorbitant prices on a trestle table, and apparently much more in several large boxes underneath.
"Can we take a look?"
"No, come back tomorrow"
"But we're here now (and aren't coming back tomorrow to look at more stuff we don't want)"
"Come back tomorrow"
"Can you tell us what you have, then we can decide whether to pop back in the morning?"
"No"
Arre - ffing -ver - ffing- derci
No wonder the Italian economy is in such a mess. I did buy 12 12mm M8 copper nuts for my exhaust studs - good deal for 6€ ..... well nearer £40 each really. But we did have a lot of laughs and the museum is good value. Never saw a single early 911 the whole trip.
Then France for a week, then back last Sunday for more engine games, and the search for Spark. I will labour this next bit for the benefit of anyone reading this in the future who has similar problems.
I did a lot of searching (as did Garry) and reading of posts here and on 911S Registry and worked through a worklist developed from that.
1. Measuring the resistance of each plug lead revealed three had no connection from one end to the other. This is because I had unscrewed the plug holder to feed the lead through the stacks and not taken enough care when refitting. Eventually got them all to show a consistent 1k ohms.
2. Using the kV unit above on my other (working/cdi/Pertronix) 911 gave 18-20kV on the lead from the coil to the cap, and ~9kV on each lead to the plugs. Doing the same on this car gave 12-18kV on the coil to cap lead, but zero to 3kV on 5 leads and 6kV on the sixth.
3. Checked the cap, changed the cap, changed the rotor arm, took out Pertronix and reinstalled points, checked and rechecked the timing. Considered if the distributor was 180deg out, checked using the mfi pump calibration mark (400 deg from TDC on No1 to FE on the pulley) as the pump belt had not been touched. Change the cdi (despite the fact it whined as it should) No change.
4. With points in there used the old fashioned method old setting the static timing when the points open on No.1. No change. At this point I also got concerned that the points orientation in my distributor was opposite to some pictures I had found on my search, and I was beginning to wonder if Neil had reassembled my distributor incorrectly (not likely I'll admit - sorry for doubting you Neil
) See my other thread on this topic
5. By this time is was clear the RH bank (4,5,6) were getting flooded (and I mean flooded!) with fuel as it was dripping out of the SSI/exhaust flange and puddling on the floor!
6. Perhaps the injectors are clogged/malfunctioning? Get them out and go to local Porsche racing outfit. Get them ultrasonically cleaned and flow tested. Reported full of crap but functional. Back in - no change. Not surprising as why would this affect the spark? Interestingly most of the injectors were stamped 227, but two were 321
EDIT: I later saw a US 911S registry thread that revealed these are Bosch date codes. 227 = July 72, and 321 = Jan73, so it is likely at least 4 are the original injectors. The less clear hand stencilled numbers vertically are cylinder numbers - the one in the photo was from No. 4.
7. I read on 911S that you could set the static timing by turning on the ignition, removing No. 1 lead and replacing with a spare coil to cap lead (so you have a bare end), and holding this 4mm from the fan housing while you slowly rotate the engine by hand, and noting where in the pulley rotation No. 1 sparks. First trial it sparked near 40 deg BTDC!??!. Rotated the distributor and repeated until it sparked on the 5Deg ATDC static timing mark. By this time I had moved the location from the previous static setting quite a bit as you might imagine.
NOW we have a good spark on all cylinders ....... but still no go. Not even the odd cough, fart, backfire ....... nothing ...... just fuel pi**ing out of the RH SSI.
Time for tea and a chat .... and a chat with my mate Tony Outridge, who put us on the track of the cold start system.
Pulled the pipe supply lines to each stack. Full of fuel, but 2 on the LH bank are blocked, despite the fact I replaced all the lines and flushed, soaked and checked each nozzle. I suppose it doesn't take much to get them blocked. Also decided to check the fuel flow from the cold start solenoid to see what rate it was and if it ever cut off. Piped the output from the solenoid into a jar, cranked it over and ..... OFF SHE WENT! Literally. We had to shut it down almost straight away as there was so much petrol coming out of the exhaust and the SSI/exhaust joint that I had left loose for this purpose. Cleaning all that up, started it again, ran a bit, stopped, cleaned up more petrol etc etc until it stopped coming. I must have mopped up over a pint of fuel in the end. No blue smoke though!
and even a video!
http://www.youtube.com/watch?v=3BSmZdfmhWM
So in summary my lessons would be...
1. With mfi if you keep cranking it over to test things each time you turn it on the cold start system operates, and will keep doing so until either you stop cranking or it fires up and the temperature switch shuts off the solenoid. It is therefore EXTREMELY easy to flood the cylinders to the point that ignition is difficult or impossible.
2. With mfi 'The search for Spark' can cause unintended secondary issues that can hide the overall problem
3. The spark test to check static timing is superior to other methods (for reasons I am not too sure!), especially if you have 'pointless' trigger mechanisms installed.
I then embarked on a 'one-at-a-time' changeover of bits back to my original intended configuration - cdi, coil, rotor, cap. I also changed the fan belt from the loose and wobbly one you can see in the video.
Seems to run well, picks up nicely with good oil pressure and no major leaks. It was too late to finalise the dynamic timing, but that will be next along with compression and leakdown tests, finishing the installation of the accelerator, clutch, driveshafts, speedo etc and give it a test run and a possible MoT.
Beer tasted good!
