RobinTR6 Posted April 22, 2015 Report Share Posted April 22, 2015 No wishing to takeover someone elses misfire post thought I'd better start anew. Car misfires above 3k revs when throttle fully open, however runs much better if revs built slowly and held (albeit still not perfect). Background....Rebuilt engine, recon'd MU, injectors, dizzy, lucas pump , PRV, new pipework throughout, new loom (and a oil filled pressure gauge plumbed into hose at MU and gauge sits on my lap), pump runs off a relay wired from alternator. Starts fine and runs great till about 3k revs then cough/cough/splutter. Pressure at MU read about 100PSI at idle but drops to about80/85 under hard acceleration (when cough/splutter starts). Tried to increase it with screw at back of PRV but no joy wont go up and when screwed ring in drops. Have spoken to Neil (Raven Smith) and he sent another PRV. (it reads 105 on his test rig). Replaced mine, symptoms same, 100PSI at idle wont increase with screw adjustment, drops to 80/85 PSI under hard acceleration. Tried, as suggested, to squeeze the output from the PRV to the tank....and whoa, pressure increases to well past 120PSI. Updated Neil and others here (thanks) and all think it must be the PRV as the pump seems capable of pushing well past the 105 spec. (Neil is sending me another which apparently is better at high pressure) HOWEVER.....been thinking:- Both refurbished and replacement PRV have same symptoms, about 100PSI at idle, dropping to 80 under load at 3k revs No fiddling with pressure screw at back of PRV raises pressure beyond 100PSI (on either PRV) squeezed output from PRV to tank pressure increases rapidly beyond 110 PSI Yep, dont ask, volts at pump 12.5, relay fed from alternator, and seperate earth to chassis Does the above point to pump, fuel flow or....given multiple PRV's exhibit same symptoms....???? Quote Link to post Share on other sites
Guest ntc Posted April 22, 2015 Report Share Posted April 22, 2015 (edited) Robin It must be the pump as it cannot cope under load. As stated before if the alternator is not required then it will reduce voltage,wire it direct. Edited April 22, 2015 by ntc Quote Link to post Share on other sites
RobinTR6 Posted April 22, 2015 Author Report Share Posted April 22, 2015 Ok, Ill wire relay direct from battery and swap pump(have a spare). Thanks Neil, heres hopeing (just passed its MOT today) so expecting to be doing some driving..... Quote Link to post Share on other sites
Peter Cobbold Posted April 22, 2015 Report Share Posted April 22, 2015 As Neil says, pump cant supply enough fuel to keep pressure up when engine is using a lot of fuel. The prv at tick over will be dumping a fast flow of fuel as the engine doesnt need it. But at full load above 3000rpm the PRV will be shut and the psi drops because the pump cant keep up. Your pressure tester sound useful. Does the oil filling make it safe from you being sprayed with fuel if it leaks? Peter Quote Link to post Share on other sites
RobinTR6 Posted April 22, 2015 Author Report Share Posted April 22, 2015 Peter, not sure but its from Hydrotechnic and is a pucker piece of kit with a takeoff at the MU so I can connect disconnect as required (hopefully wont be required for too long now....) Quote Link to post Share on other sites
RobinTR6 Posted April 22, 2015 Author Report Share Posted April 22, 2015 Guys, still !"£$%&*&. Another recon'd pump with the original recon'd PRV, same symptoms (havent driven it ), ie 80 ish PSI at idle, couldnt get it any higher. Tried the replacement PRV and guess what ....same. So doesnt sound like its eithe the pump nor the PRV. Tank was clean when I refitted it, standard outlet ...only difference is a petrol tap between tank and Lucas filter ...could it be a flow issue. With the return to tank unhooked and ignition on theres a steady flow flying out of the PRV.... Quote Link to post Share on other sites
TR NIALL Posted April 22, 2015 Report Share Posted April 22, 2015 Put up a Picture of your Set Up in the Boot,we may see a Problem. Quote Link to post Share on other sites
Steves_TR6 Posted April 22, 2015 Report Share Posted April 22, 2015 I was going to suggest tank outlet is inadequate, but it may be the tap. Was advised against fitting a tap. What pump are you running Robin? Quote Link to post Share on other sites
RobinTR6 Posted April 22, 2015 Author Report Share Posted April 22, 2015 (edited) Ok here goes, Doctor Lucas all the way, pump and filter. Could it be the tap, turns off fine and defo lets petrol flow when open'd. Pump Boot setup Edited April 22, 2015 by RobinTR6 Quote Link to post Share on other sites
marko Posted April 22, 2015 Report Share Posted April 22, 2015 It is clearly a restriction in the flow....I've never seen any plumbing quite like that....I suspect the tap or pipe is to small a bore and hence limiting the fuel flow.....does the pump get hot or make strange squeeling noises? Quote Link to post Share on other sites
Guest ntc Posted April 22, 2015 Report Share Posted April 22, 2015 It is clearly a restriction in the flow....I've never seen any plumbing quite like that....I suspect the tap or pipe is to small a bore and hence limiting the fuel flow.....does the pump get hot or make strange squeeling noises? +1 and a Lucas pump is also a suck pump ? never seen one fitted like that. Quote Link to post Share on other sites
RobinTR6 Posted April 22, 2015 Author Report Share Posted April 22, 2015 (edited) Pump mounted on chassis where the Bosch pump sometimes goes. Its in a saloon cradle hence its on its side. Pipework is standard, agreed next step is I'll change feed from tank and omit tap....pump ocassionally wheezes but doesnt scream. Have done 3k miles with this setup , no overheating of pump etc. Also checked setup and location with Neil (Raven) before installing. Edited April 22, 2015 by RobinTR6 Quote Link to post Share on other sites
peterq Posted April 22, 2015 Report Share Posted April 22, 2015 Hello Robin, Looking at your picture of the pump, I assume the hose at the right on top is going to the engine. The braided hose seems to be twisted? This would give a restriction after the PRV: - at low rpm the PRV works as adjusted. - at high rpm the flow increases, the restriction builds up pressure and the PRV opens, the pressure before the MU drops. If my assumption is correct then measuring direct at the exit of the PRV would give correct readings. Hoping this helps...... Kind regards, Peter. P.S. He who does not like braided hoses...... Quote Link to post Share on other sites
TR NIALL Posted April 22, 2015 Report Share Posted April 22, 2015 (edited) I'm not saying it's not right but it looks a very weird set up. I use a Cut Off Tap and a 8mm Glass Inlet Filter and don't have any problems with Flow. Edited April 22, 2015 by TR NIALL Quote Link to post Share on other sites
Peter Cobbold Posted April 22, 2015 Report Share Posted April 22, 2015 The pump is pumping downwards (I think) so any air/vapour bubbles might keep floating up into the gears. That might not help pumping. That wont happen with the pump vertical, the bubbles will go off upwards to the PRV. And I cant see the green plastic weep tube from the base of the pump to air. Could that be an issue ? Peter Quote Link to post Share on other sites
RobinTR6 Posted April 23, 2015 Author Report Share Posted April 23, 2015 What size is the pipe from tank to filter, Lucas filter that is. Quote Link to post Share on other sites
TR NIALL Posted April 23, 2015 Report Share Posted April 23, 2015 Rob,if you have the Uprated Outlet from the Tank it has an inside Diameter of 7mm and Takes an 8mm I/d Pipe. Quote Link to post Share on other sites
TR NIALL Posted April 23, 2015 Report Share Posted April 23, 2015 This is the set up I'm running with No Problems. Quote Link to post Share on other sites
RobinTR6 Posted April 23, 2015 Author Report Share Posted April 23, 2015 Thanks Niall.None of the hoses are twisted or compressed its just the angle of the photo. I'll try replacing the hose from the tank as the tap could be a restriction. Still bemused by the fact that compressing the outlet from pump to tank increases pressure to 120 psi.If the pump isn't man enough or lacks flow why would compressing outlet in create pressure at MU ? Quote Link to post Share on other sites
TR NIALL Posted April 23, 2015 Report Share Posted April 23, 2015 First check I would do is disconnect inlet to filter get a bucket/Basin and see if your getting full flow from the Tank,leave Tap in place for this and try not to Smoke. Quote Link to post Share on other sites
RobinTR6 Posted April 23, 2015 Author Report Share Posted April 23, 2015 OK will do, cigs will be left. Quote Link to post Share on other sites
Peter Cobbold Posted April 23, 2015 Report Share Posted April 23, 2015 (edited) Robin, You asked: ""Still bemused by the fact that compressing the outlet from pump to tank increases pressure to 120 psi.If the pump isn't man enough or lacks flow why would compressing outlet in create pressure at MU ?"" Because at tickover bu**er all fuel is being taken by the engine and the PRV is dumping most of the pumped flow. So when you compress the overflow psi rises. BUT when driving the engine is using much more fuel, and more than the pump can supply at 105 psi so the psi you measure drops. If you were able to compress the overflow while driving you'd find the psi would not rise and would be around 85 as measured. Peter Edited April 23, 2015 by Peter Cobbold Quote Link to post Share on other sites
Rob Salisbury Posted April 23, 2015 Report Share Posted April 23, 2015 Robin, I seem to remember that the Lucas pump should deliver 16gallons @100psi in one hour, (thats 1.2litres/min), so you may want to check that. Cheers rob Quote Link to post Share on other sites
astontr6 Posted April 23, 2015 Report Share Posted April 23, 2015 Dear Robin, Your fuel supply system look very complicated to me? Observations: 1) As already stated what is the bore size of the pipework from tank to pump ? 2) What is the bore sizes of the fittings from Tank to Pump? Was a very well known problem area 40 years ago! 3) The CAV filter head is not plumed as per original TRs that I have seen? The original uses one take off in the front and the other is taken off from the back by a Banjo fitting. 4) Have you the petrol filter in the CAV unit? It is different to the diesel filter? 5) Most important of al,l the gravity flow rate to the Lucas Pump S/B 1 l/min + minimum?. 6) Triumph (London) introduced a mod done by CAV Dealers in this area, where the filter head was changed to use 3/8" bore pipework/fittings for problem cars. 7) Is your Lucas Pump still able to produce the pressure? If not,my view is go Bosch! Bruce, Quote Link to post Share on other sites
ijonsson Posted April 23, 2015 Report Share Posted April 23, 2015 (edited) Can't help it, but this hose looks flat to me! Edited April 23, 2015 by ijonsson Quote Link to post Share on other sites
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