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TR5tar

I've got problems ... and for once, they are car related

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Hello, 

It's quite refreshing to be talking with folks about car related issues, rather then ... well, you know what.

I've asked a few friends about this one already, but haven't come to a conclusion as to what is going on. History is this:

Car, TR5, on electronic ignition and PI, has been running pretty smoothly for the last few months. After a few weeks non running, when I started her up earlier in the week, it sounded a bit rough, so I took her for a spin and found that after a few miles the engine seemed very rough, and the car jolted on coming off the gas. It didn't seem too bad under acceleration, but a bit hesitant, and it got progressively worse.  I filled up on this drive, and stuck some Redex injector cleaner in. I did wonder if that has caused issues, but the problem was developing beforehand. 

Anyhow, on returning home, I pulled the plugs and they were all very black, which indicates too rich a mixture or weak spark, right? Although, I did not see any black exhaust smoke, which might be expected?  At this point I changed the plugs and checked that the MU fuel enrichment lever on the MU and the choke were both returning as they should . . . they are both fine. I also changed the rotor arm. All the injector lines have a strong pulse and each seems to be spraying correctly, although I noted a slight drip on one.  

When I started the car this morning, engine sounded pretty good, so I decided to go for a blast. Car was pretty good for the first few miles, but then problems similar to before arose. This time, however, the car didn't jolt when off the gas, but it did when the gas was applied. Along with the jolting it also backfired as I applied the gas. I had to give it a boot full of acceleration to pull off and it seemed very down on power. Backfire suggests over fueling, right?

Back home, I changed the coil, and dissy cap. I've not taken her out again to see if any of that as made a difference, but when idling I note that every 8 seconds or so the revs pick up slightly for a couple of seconds and then die down again. Is that significant?

Friends have suggested MU needs looking at. Does everyone here concur, or is there something else to check that might be causing this?

Cheers, Darren

      

Edited by TR5tar

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Darren, It might be the PRV sticking leading to over-rich fuelling ( which will be better tolerated while the engine is cold or warmng up)

With the engine ticking over give the PRVa thump or two.

Peter

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Diaphragm suck test? That is, unplug the tube that connects the MU with the inlet manifold at the manifold end and suck on it. You should be able to pull a vacuum and the vacuum should hold if you block the tube with the tip of your tongue. If you are just sucking air, either tube or the diaphragm in the MU has split and the air leak will cause rich running.

If running NGK plugs there may be further issues arising as some of them seem unable to cope with being fuel wetted and just stop working.

when you say "backfire", is this from the exhaust (what I would call a backfire) or under the bonnet, through the air filter (which is what I'd call "spitting back". The former is most likely rich and the latter most likely lean, though mis-timed sparks could cause either.

Nick

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I could very well be wrong, but if timing was out wouldn't the issue have been evident immediately? I will check it, but distributor is tight in place and I haven't moved it at all. Dizzy cap is tight too. 

Confess that I don't know where the PRV is Peter. If I can locate it, I'll try your suggestion.

Thanks for the suck test suggestion Nick. Tried it, but I'm not sure. On first suck I heard click from MU. There was a very slight hiss when I removed my tongue, but nothing much. Not sure I'm doing it right.

Cheers, Darren

   

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By the way Nick, yes the backfire was from the exhaust. If the diaphragm in the MU is split, is that something I can easily change, or is it a case of sending the MU off to be refurbished? 

I did wonder about the timing. Have to say that I'm not sure if I'm reading the timing right. There are three marks (shown in photo), but I'm not sure what exactly they relate to. I think the wider white mark (the bottom of the three) is the one I am reading and that's 12 degrees ... ATDC I think. Would that be right? Apologies, I'm a bit dopey when it comes to this. 

Cheers, Darren 

IMG_1654.JPG

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15 hours ago, TR5tar said:

I could very well be wrong, but if timing was out wouldn't the issue have been evident immediately? I will check it, but distributor is tight in place and I haven't moved it at all. Dizzy cap is tight too. 

Confess that I don't know where the PRV is Peter. If I can locate it, I'll try your suggestion.

Thanks for the suck test suggestion Nick. Tried it, but I'm not sure. On first suck I heard click from MU. There was a very slight hiss when I removed my tongue, but nothing much. Not sure I'm doing it right.

Cheers, Darren

   

Darren, The Pressure Reiief Valve is between the passneger side inner wheel arch and the fuel tank, near the fuel pump. Peter

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Hi Peter, 

Not sure what it looks like. Is it visible in either of these two photos. First is of the pump and filter under wheel arch, second is of what I assume is another filter under the fuel tank in the boot. 

 

IMG_1689.JPG

IMG_1692.JPG

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Thanks Kev. I'll try giving it a thump with engine running, as Peter suggests. If that doesn't make a difference, I'll try cleaning it. Is it just a case of undoing the nuts at each end and then removing the centre piece? Any special procedure? Will I get a load of fuel piddling out when I do it? What's the best way of cleaning out the strainer? Apologies for all the questions. 

If it's not the PRV, then is it most likely to be the MU, given the symptoms? 

One other thought crossed my mind and that is that I've not checked the valve clearances since I've had the car. I f they are out, could that account for any of this?

Thanks for everyone's input. 

Cheers, Darren    

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Only as an aside, spotted in the above pics NGK Iridium plugs, is that what you are using, whilst a nice plug in something with accurate fuel control those  iddy biddy point central electrodes are easily fouled, also the Iridiums are supposed to come pre gapped and your not supposed to try altering them, and most I have seen have a far wider gap than the 25-28 I'd expect you to be running. May not be a cause of over richness, but may contribute as if they are getting a bit fouled, then they may be missing and getting even more fouled in a vicious circle.

Ok course you are now going to post that the boxes are incidental and kicking around in the boot from when you did the EuroHatch last month :biggrin:

Alan

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Would you count Pi as "accurate fuel control" ,Alan?   I use them on the race car, no fouling probs.

J.

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1 hour ago, JohnD said:

Would you count Pi as "accurate fuel control" ,Alan?   I use them on the race car, no fouling probs.

J.

Accurate......:ninja: hmmmm.

The capability is there, to a point, but many examples seem to be more akin to pressure washers 

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7 hours ago, JohnD said:

Would you count Pi as "accurate fuel control" ,Alan?   I use them on the race car, no fouling probs.

J.

I have no doubt that your's is set up as well as it can be John :yes:  I was just postulating that if a car was having rich fouling problems (and we know the TR5 has to run slightly rich anyway) that the Iridium's tiny tip may be even more suspect to the problem. Nothing against the plug, in fact just removed and replaced a set in the Cosworth engine.

Alan

 

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On 9/13/2018 at 5:19 PM, TR5tar said:

Thanks Kev. I'll try giving it a thump with engine running, as Peter suggests. If that doesn't make a difference, I'll try cleaning it. Is it just a case of undoing the nuts at each end and then removing the centre piece? Any special procedure? Will I get a load of fuel piddling out when I do it? What's the best way of cleaning out the strainer? Apologies for all the questions. 

If it's not the PRV, then is it most likely to be the MU, given the symptoms? 

One other thought crossed my mind and that is that I've not checked the valve clearances since I've had the car. I f they are out, could that account for any of this?

Thanks for everyone's input. 

Cheers, Darren    

Hi Darren

There will be a little seepage of fuel but it doesn’t pour out. There is the same type strainer in the fuel pipe to metering unit too. I have the Lucas pump and there is one there too (you have the Bosch type pump so unlikely there’s a strainer there) which collapsed and restricted the fuel flow which made my car stop. 

Good luck in finding your problem. 

Could you borrow a pressure gauge from any one local? 

All the best Kev.

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Thanks Kev. A friend gave me a call a couple of days back and talked me through some checks. He has a strong suspicion about the problem and I'm working on it at the moment, with his very patient guidance. Fingers crossed. I'll tell more later ... when I've finished putting the engine back together :sick: I'm hopeful that it'll fix it, but if not I'll try your suggestion. It's all a bit of detective work.

I am indeed using the Iridium plugs in the TR Alan. I've used them for about three years and never had any fouling issues. They appear to be very good, but I accept that it could be psychological, and they may in fact be no different to the standard plugs. Anyhow, I think I go faster, therefore I go faster! Not, however, using them on the eurobox Alan ... because I haven't got a eurobox :biggrin:

  

Edited by TR5tar

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Darren,

 

What electronic ignition are you running? Sounds like it's breaking down when hot. If you have an external control box, check if it's hot to touch. If so throw it away and get back on points/condenser set up!!

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Thanks for the suggestion Tom, but we think we have nailed it down to something else. Will report back when it's fixed. 

Darren 

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