JohnTee Posted February 6 Report Share Posted February 6 (edited) My 6 has started 'stuttering' at low speeds. It's fine above about 45mph, but shudders below that speed. The problem appears to be cylinders 1, 2 and 3. 4, 5 and 6 are behaving themselves. Injectors have been bled, plugs and points cleaned and gaps set. Timing checked. Fuel pressure 104 psi. Has anyone come across this problem before? Any insights into the problem? Have I missed something glaringly obvious? Any assistance gratefully received. Thanks in advance. John Edited February 6 by JohnTee Typo Quote Link to post Share on other sites
john.r.davies Posted February 6 Report Share Posted February 6 That points away from an ignition or fuelling problem and to something more local to those cylinders. Compression test indicated. John Quote Link to post Share on other sites
Mike C Posted February 6 Report Share Posted February 6 How do you know it's these cylinders-"The problem appears to be cylinders 1, 2 and 3"? Quote Link to post Share on other sites
Steve 286 Posted February 6 Report Share Posted February 6 Hi John does it tick over ok or missing if missing I would pull one injector at a time when running you may find one or two still have air in them the rpm will drop if you pull out good running injector Quote Link to post Share on other sites
JohnTee Posted February 6 Author Report Share Posted February 6 Thanks guys. John - Compression. It's just had a professional engine rebuild. Everytning good. Mike - Remove plug leads from 1, 2 and 3 sequentially-little change. Do the same with 3, 4 and 5 sequentially, noticeable difference in running. Also the exhausts are different. Steve - tick-over is rough. The injectors have been bled, spray cones are good. It's got me stumped John Quote Link to post Share on other sites
Steve 286 Posted February 7 Report Share Posted February 7 Hi John if it’s got a rebuilt engine obviously the compression should be good but have you checked it that would be the first thing I would do presuming it’s got new spark plugs in it you’ve got to determine what actual cylinders are Causing the issue The way you’re talking about it clearing when the revs get up I’ve got a gut feeling you’ll end up finding you’ve got a injector issue Once you know what’s Cylinders are causing the issue I would remove the injector and blown through with an airline only other thing it might be is the butterflies out of synchronisation but I’m clutching at straws here it would probably be too obvious Quote Link to post Share on other sites
JohnC Posted February 7 Report Share Posted February 7 (edited) Given that you can isolate the problem by pulling plug leads, that does indicate that you've already isolated the problem. Have you tried swapping leads to see if the problem moves with them? My go-to if cylinders are behaving differently is: first, spark (check the plug gap and condition, swap the cables around to see if it moves the problem); second, throttle balancing (it does take patience to get right); and third, valve clearance. PI problems a distant last. In 39 yrs of TR ownership I've only had to fix the PI twice. Once because the internal seals had decided that 40yrs from new was time for retirement, and once because the injectors decided that the same was true at 50yrs. As always, YMMV. Cheers, JC Edited February 7 by JohnC re-read OP post Quote Link to post Share on other sites
JohnTee Posted February 7 Author Report Share Posted February 7 Steve- compressiin tested and spot on. Plugs all good, all sparking, all smelling of fuel. I'm starting to think air plenum problems. Injectors 1, 2 and 3 swapped with 4, 5 and 6, problem stays with 1, 2 and 3. Same with plugs. Swapped plug leads for a spare set, no change. Found there was an o ring missing between metering unit and pedestal, that's being fitted tomorrow. Might be clutching at straws, but here's hoping. JohnC - testing so far has pretty much rulled all that out. As the nice man in the garage says, the engine is good after the rebuild in Nov-Dec last. It's one of the bits thats bolted onto it. Thanks for your time and input, guys. Much appreciated. John T Quote Link to post Share on other sites
Peter Cobbold Posted February 7 Report Share Posted February 7 Firing order is 1 5 3 6 2 4. Could be the MU shuttle failing to deliver correct fuel to 1-3-2- but OK for -5-6-4. but only at low loads. Try an Italian tune-up ? Quote Link to post Share on other sites
BlueTR3A-5EKT Posted February 7 Report Share Posted February 7 12 minutes ago, Peter Cobbold said: Firing order is 1 5 3 6 2 4. Could be the MU shuttle failing to deliver correct fuel to 1-3-2- but OK for -5-6-4. but only at low loads. Try an Italian tune-up ? That would be my approach but this engine is said to have had a recent professional rebuild. Such action might impair any warranty. Shuttle movement is an interesting possibility Tappet clearances all as per the book? Quote Link to post Share on other sites
JohnTee Posted February 7 Author Report Share Posted February 7 Peter, 15 too young, 36 too old, 24 just right. I had discounted the MU as there appeared nothing linking 1, 2 and 3 as there didn't appear to be anything adjacent to the 3 of them but looking at it from that perspctive opens up new possibilities. Thanks for the mental nudge. Got me wondering, now. Blue- tappet clearances as per service manual. Thanks, gents. Hopefully, it'll be tracked down, it's just a shame I'll miss Saturday's ride out to Gaydon. John T Quote Link to post Share on other sites
Bluestone Posted February 7 Report Share Posted February 7 Hi John, Had a similar misfire on my 6 a few years ago. Turned out to be loose / corroded metal joints on the end of a couple of HT leads where they fit into dizzy cap. New joints did the trick. From your swapping of components, maybe worth investigating the distributor cap, as that appears to be the constant for taking your sparks to cyls 1, 2 and 3? How are the internal pick up points where the rotor arm passes, or there may be a hairline crack in the cap itself? Simple enough to try a good known spare or new distributor cap before delving into the MU etc. Cheers Ray Quote Link to post Share on other sites
Neil Ferguson Posted February 7 Report Share Posted February 7 Have the injectors been fitted in the correct firing order. What was it like before the rebuild. Quote Link to post Share on other sites
JohnTee Posted February 7 Author Report Share Posted February 7 Ray, New plugs, new leads, new distributor cap, new rotor arm. As soon as I get it back from the garage, the dizzie is coming off for a trip to the Distributor Doctors, as it's a little worn. It's always possible that one of them may be duff, so I'll try that when I get the car back.They're loathe to let it go when it's not 100%, but I have the time to play with it, and I work cheap. Neil, It was doing it to a certain extent. Gradually growing worse last year, the the head gasket went and I was thinking it might be associated with that.Obviously not. Thanks for your input, guys, gratefully received. Best wishes, John T Quote Link to post Share on other sites
PodOne Posted February 7 Report Share Posted February 7 Just my very limited experience with PI and regard to the MU shuttle. The fuel pressure will be constant at low speed or high speed and the injectors seem to be giving a good cone pattern at idle which would suggest it's not likely to be involved. The problem seems to be at a certain rpm/speed. From my dealing with cars and misfires and stumbling it's nearly always been an ignition issue. I'd be changing the points and condenser or if you have EI unit fitted back to points and changing the cap/rotor arm and go from there. Andy Quote Link to post Share on other sites
Jonny TR6 Posted February 7 Report Share Posted February 7 How are all the butterflies looking at idle ? Have you done a snail meter test ? Have the throttle bodies been touched in the rebuild ? Just a few thoughts after renewing my throttle bodies. Quote Link to post Share on other sites
Macleesh Posted February 7 Report Share Posted February 7 Another vote for an Italian tune up here. Mine had a similar issue, driving it hard seemed to sort it. Quote Link to post Share on other sites
JohnTee Posted February 7 Author Report Share Posted February 7 Thanks for the suggestions, gents. Plenty to chew over there. I'm off to the Stoneleigh spares show on Sunday, so I'll invest in a new ignition system and see if that does anything to obviate the problem. Cheers, m'dears. John Quote Link to post Share on other sites
Steve 286 Posted February 7 Report Share Posted February 7 I’ll be there as well meeting Tom Cox to give him my gearbox for rebuild Quote Link to post Share on other sites
JohnTee Posted February 8 Author Report Share Posted February 8 Success! Just had the garage on the phone. When the chap I bought it off re-built it, putting the re-conned metering unit on he seemingly used silicon sealant when fitting it, rather than the correct O-Ring. Over the course of a few years, it has obviously deteriorated. Fitting the correct seal has returned it to its former running glory. Colour me happy and content. Thanks to all for your time, advice and opinions. Much appreciated. John T Quote Link to post Share on other sites
john.r.davies Posted February 8 Report Share Posted February 8 (edited) That's good news, John! Thanks for the feedback! It was fuelling all along. I would suspect bits of sealant got into the lines! Edited February 8 by john.r.davies Quote Link to post Share on other sites
Jonny TR6 Posted February 8 Report Share Posted February 8 Happy days - bizarre that the cones were all spraying correctly. Quote Link to post Share on other sites
Bluestone Posted February 8 Report Share Posted February 8 Great result John T And excellent garage work tracing the problem. Ray Quote Link to post Share on other sites
Mk2 Chopper Posted February 9 Report Share Posted February 9 I would imagine the silicone blocked the return line, causing incorrect fueling due to diaphragm displacement, or If some made it's way back to the tank it could have got taken back through the MU. Either way a unusual thing to have happened, but glad it's been resolved. Gareth Quote Link to post Share on other sites
JohnC Posted February 10 Report Share Posted February 10 (edited) On 2/9/2024 at 2:02 AM, JohnTee said: Success! Just had the garage on the phone. When the chap I bought it off re-built it, putting the re-conned metering unit on he seemingly used silicon sealant when fitting it, rather than the correct O-Ring. Over the course of a few years, it has obviously deteriorated. Fitting the correct seal has returned it to its former running glory. Colour me happy and content. Thanks to all for your time, advice and opinions. Much appreciated. John T That’s one for the “never would have thought of that” book. Great job by the garage. Me, I’d drop by a slab of beer. But this is Australia Which O ring BTW? JC Edited February 10 by JohnC Quote Link to post Share on other sites
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