| Author | Message | ||
     John G. Frequent User Username: john116 Post Number: 68 Registered: 4-2012 |
I know it's hard to diagnose from just a text description, but thought it was worth a try. Am still trying to get SRH40222 back on the road after many years of work (although with many months in between of no progress due to work/life etc). Engine runs currently, but roughly. Over the last few years, have replaced electronic ignition, coil spark plug wires, spark plugs, ballast resistor. Current status: Running roughly Taking spark plug leads off plugs in turn indicates that cylinders A2 and B4 are not doing anything (no change in speed or roughness) Tested spark OK at spark plug end of leads Not sure if the fact A2 and B4 are affected is just coincidence or something else? | ||
| Christian S. Hansen Grand Master Username: enquiring_mind Post Number: 815 Registered: 4-2015 |
compression check results? may assist with diagnosis...or not. | ||
| Vladimir Ivanovich Kirillov Grand Master Username: soviet Post Number: 998 Registered: 2-2013 |
John maybe check distributor cap for cracks | ||
| Trevor Pickering Experienced User Username: commander1 Post Number: 42 Registered: 6-2012 |
Hi John When you replaced the the plug wires did you make very sure that you did them in the correct order in the dizzy cap? Sorry if this seems obvious but its easy to make a mistake like this. I have!!! regards Trevor | ||
| John G. Frequent User Username: john116 Post Number: 69 Registered: 4-2012 |
Distributor cap new, compression was OK when checked a while ago, and I have double, triple, quadruple checked the spark plug wires are in the correct places. Thanks for all the suggestions though. | ||
| Jeff Young Grand Master Username: jeyjey Post Number: 373 Registered: 10-2010 |
So you say you're getting spark at the plug end on A2 and B4, but they're not firing? If so, a compression check of those two cylinders would definitely be in order. If they fail, a leak-down test will tell you where the problem is. | ||
| Geoff Wootton Grand Master Username: dounraey Post Number: 1984 Registered: 5-2012 |
A2 and B4 are on the same carburetor. As a matter of course I would make sure the carbs are balanced correctly, just to eliminate that possibility. | ||
| Mark Aldridge Grand Master Username: mark_aldridge Post Number: 550 Registered: 10-2008 |
Consider buying Kelly Opfar' carb setting tool.By using this together with a rev counter I have balanced the Shadow at Idle, adjusted out linkage wear,balanced on throttle and accurately balanced the mixture by measuring piston lift/ RPM. -- Invaluable. Also done the S1,and Sprite.Far more accurate than ear !The cars sound and run better than they have for years. Mark | ||
| Omar M. Shams Grand Master Username: omar Post Number: 1575 Registered: 4-2009 |
Dear John, please do the following tests in order: take a good spark plug that you know works and connect it to the end of the A2 lead whilst the original plug is still in place. run the car and look at the plug when connected to earth to see if you are getting the slave plug to spark. The spark needs to be strong and healthy. Do the test again for B4. If they both spark then change the spark plugs in these cylinders. New spark plugs have been known to be duds in the past. If there is no difference after all this - we need a compression test. If that reveals good pressure then we start to talk carbs. Let us know what happens. | ||
| John G. Frequent User Username: john116 Post Number: 70 Registered: 4-2012 |
OK - thanks, will do. Will update as soon as I've done that. | ||
| John G. Frequent User Username: john116 Post Number: 71 Registered: 4-2012 |
Hi - also, thanks for the carb balancing suggestions, have the tools and gauges for that already and have balanced them. | ||
| Mark Aldridge Grand Master Username: mark_aldridge Post Number: 551 Registered: 10-2008 |
John, were the carbs much out of balance before you adjusted them ? If not, I am still thinking ignition. Can you substitute the leads and plugs on A2 and B4 ? Can you substitute the cap and rotor ? Mark | ||
| Robert J. Sprauer Experienced User Username: wraithman Post Number: 38 Registered: 11-2017 |
Sounds like 2 bum ignition leads. Because they are new does not guarantee they are working. I have witnessed new sets (cheap subs for the originals) they fail. Always keep your old ones or atleast the longest lead to use as a test backup to rule out a bum lead. Also double check and make sure the connections "click". Also cheap dizzy caps will have the same results. | ||
| John G. Frequent User Username: john116 Post Number: 72 Registered: 4-2012 |
Swapped out the possible bad spark plug leads for two known good ones, this made no difference. Then checked the spark with a known good spark plug on those same two cylinders. Result in video below (sorry it's blurry). Spark seems weak/inconsistent to me. Also tested it on a 'good' cylinder, but spark condition seemed to be the same. http://60.240.221.94/RR_spark.mp4 | ||
| Christian S. Hansen Grand Master Username: enquiring_mind Post Number: 816 Registered: 4-2015 |
Irrespective of "ok a while ago" re-do compression test on those cylinders. | ||
| John G. Frequent User Username: john116 Post Number: 73 Registered: 4-2012 |
Christian - will do, is next on the list of things to check. | ||
| Vladimir Ivanovich Kirillov Grand Master Username: soviet Post Number: 999 Registered: 2-2013 |
John you certainly have a curly problem. If you have an ohms meter the resistance in each ignition lead should be less than 700 ohms per metre. Hope I am right on that and feel free to correct me if I'm not. Next run the engine and spray carburetter cleaner all over the intake. If doing that causes an increase in RPM then you have an airleak. Holden Comodores that use a Buick style V6 are often found to have leaking intake manifold gaskets. Same test should work on RR/B. Here is my last hunch but its an outside bet. Sticky valve stems. To diagnosis I remove the valve covers and rockers, put piston at BDC and hit the top of the valve. You'll know by the sound if you have a sticky valve. I agree that a new part especially anything electrical can definitely be a faulty part. I am always suspicious of anything Lucas new or old . | ||
| Patrick Lockyer. Grand Master Username: pat_lockyer Post Number: 1900 Registered: 9-2004 |
IMO this can be the start of a electronic distributor Lucas 25 de8 failing. Check the dwell and then test as previous postings on here a while back. | ||
| ross kowalski Grand Master Username: cdfpw Post Number: 834 Registered: 11-2015 |
John, Poor running is always a little harder than a no start. No start is always something big, poor running, could be quite subtle. On a very big plus side, your weak cylinders are consistently the same two. That makes diagnosis easyish. If I arrived at your garage first thing I would do is ask you to pull the cap lead and crank the car and ignore any diagnostics you provided. The starting part is to listen to it crank. If it isn't even there is uneven compression between cylinders. Basically the rule on compression, you need some to run and you need it the same on all bores to tune an engine and have it run well. The ignoring any previous diagnosis is also key because it prevents objective evaluation of the facts. If you want to learn how to hear bad cranking, pull a plug and listen. That's what a holed piston, destroyed valve, bent valve, or stuck valve sounds like. If it's subtle I would put on a gauge, but pretty much if you can hear it in the crank that's not great. Then I would run it pulling ht leads with a tachometer to see the weak cylinders. If the compression is good pull out your timing light and check each wire watching the flash consistency. Every plug wire should be even and consistent. If no, then you have a distribution problem. If the flashes are even swap the plug wires and plugs and see if the same two bores are dead. If they are then you are left with fuel mixture. I trouble shoot problems all the time with engined of all sorts, half the time because it's a tricky one that someone is struggling with. I always find out where the root cause lives fuel/spark/compression then find out if it's electrical or mechanical. Good luck. | ||
| Vladimir Ivanovich Kirillov Grand Master Username: soviet Post Number: 1000 Registered: 2-2013 |
John I know this problem you are having must be very frustrating to the point of driving you nuts. Its faults like this that cause mechanics with many years of experience to reach for the bottle, pack up their tools and never return to the trade and proceed in another career like truck driving. And it's also problems like this that financially destroy mechanical repair businesses because its the workshop that wears the cost as you cannot say to the customer "the fault was difficult to locate, but we finally found it, she's running beautiful now and that will be $10,000". People just will not wear it and will never try to understand it. But John, when you do find the problem, you will be covered with a rush of warm ecstacy similar to MDMA. Please post the fault once located as it may save another custodian a hell of a lot of pain and frustration. | ||
| Jim Walters Prolific User Username: jim_walters Post Number: 179 Registered: 1-2014 |
John, I think Ross is right on the money when he states "ignoring any previous diagnosis is also key because it prevents objective evaluation of the facts". After watching your video, here are my observations: Your spark appears weak and variable. It definitely misfires at the 5 second mark. Four times it is a big bright spark. All others are very small. In my experience this points to a coil/condensor/OPUS module fault. Rule out the condensor as you have electronic ignition fitted. That leaves the coil or module. I have come across a strange situation in the past where the coil is failing and it seems like it does not have enough time to fully build up a charge. It appears to be fine for three firings then every fourth it produces a poor spark. This diagnosis may not seem logical and I really can't see how it could act like that but replacing the coil solved the issue more than once. I don't think it is a coincidence that the dead cylinders are supposed to fire 180šapart. You state you have replaced the electronic ignition, coil, spark plug wires, spark plugs, ballast resistor, distributor cap. Did you replace the rotor? What electronic ignition is fitted? Is it the OEM Lucas OPUS or another type? Can you confirm is the coil new and the correct ohm value? I'm assuming here that you are sure the compression is OK, and that the parts you have replaced are new and functioning properly. Also, I cannot tell the colour of the spark in your video. It should be blue if the ignition system is working correctly, if yellow/orange it is weak and that indicates a fault in the system. One other thing, carbon core resistor spark plug leads should measure 10,000 to 20,000 ohms per foot of length. The statement of less than 700 ohms per metre is not correct. SRH8505 SRC18015 SRE22493 NAC-05370 www.bristolmotors.com | ||
| John G. Frequent User Username: john116 Post Number: 74 Registered: 4-2012 |
All, many many thanks for all your suggestions. More diagnosis on my part to do. Jim - the electronic ignition was a rebuilt Opus unit from a well known UK RR spares supplier. Rotor and distributor cap were new as well. Coil was also new. I'm wondering if I have a new faulty coil? In an attempt to get the car to wake from it's slumber, I replaced all the ignition components. Which coil to use is confusing somewhat - any suggestions appreciated. | ||
| Martin Taylor Prolific User Username: martin_taylor Post Number: 132 Registered: 7-2013 |
Turn your dizzy by 45 degrees in what ever direction allows movement and move the leads one space back, this will test your distributor for worn bushings or loose magnets, if the fault moves look at the dizzy, if it stays the same you will know this part is ok | ||
| Jim Walters Prolific User Username: jim_walters Post Number: 181 Registered: 1-2014 |
So the fault appeared only after you replaced all the ignition? It is not unheard of to find a brand new coil faulty right out of the box. I always test them before installation now to ensure they are working correctly. With the OPUS ignition system your coil should measure no more than 1 ohm. Also, before you get into replacing any parts recheck your air gap on the pickup. It should be .014 to .016 thou. More than that can cause a misfire on one or more cylinders. SRH8505 SRC18015 SRE22493 NAC-05370 www.bristolmotors.com} | ||
| Vladimir Ivanovich Kirillov Grand Master Username: soviet Post Number: 1001 Registered: 2-2013 |
John - Coils - The old silver metal canister coils used to last for decades. The squat little coils last years to months. Mallory makes heavy duty coils and I will be putting that type of coil on my Spirit and Camargue as soon as their silver metal canister coils fail. Furthermore, I will be moving the position of the coil from its hideous original position on the back of the engine near the distributor subjecting it to intense heat and vibration to some convenient place on the body. Jim thanks for that correction on the ohms test for leads. Workshop manuals are great. And often useless. I just checked a Ford Falcon, 1976 Cadillac, and Shadow Manual TSD 2476 and could find no info on ohms testing HT leads. You say 10k to 20k ohms per foot. First entry on google says 10k to 12k. Jim 8,000 ohms difference! I would stick to 10,000 at most. I think I was definitely told to chuck anything over 7,000 in the bin when I worked at an exotic cars repair shop decades ago. | ||
| Patrick Lockyer. Grand Master Username: pat_lockyer Post Number: 1901 Registered: 9-2004 |
Dwell [air gap] 33-39 any greater variation will point to shaft run out!!!!!!!! Run dwell to the lowest clearance to test. IMO the coil is OK. | ||
| Patrick Lockyer. Grand Master Username: pat_lockyer Post Number: 1903 Registered: 9-2004 |
BTW the higher the figure [dwell] the closer the gap. | ||
| Trevor Pickering Experienced User Username: commander1 Post Number: 44 Registered: 6-2012 |
Could someone please post what carb feed what cylinders please as I am trying to track down a problem. many thanks Trevor | ||
| richard george yeaman Grand Master Username: richyrich Post Number: 981 Registered: 4-2012 |
Trevor bank A carb. feeds the two outer cylinders on bank A and the two inner cylinders on bank B and so on. Richard. | ||
| Trevor Pickering Experienced User Username: commander1 Post Number: 45 Registered: 6-2012 |
Many thanks Richard all is now clear regards Trevor | ||
| Patrick Lockyer. Grand Master Username: pat_lockyer Post Number: 1906 Registered: 9-2004 |
copy of a odd event. May help if all other checks seem ok. [Fitted carburettors yesterday checked timing balanced with dial gauges check mixture with colour tune and now it's running better than it ever has , would never of looked for one carburettor jet falling apart hope this may help others but think it's rather rare thing to happen!] |
