Hi all, I am running out of ideas on this one. I am only getting around 13mpg from my 3500 EFI auto. I am driving gently but cant get it to increase. I am not using the computer to give me the MPG, I am working it out and have confirmed the speedo mileage is correct. Having worked through Ramons guide, I have a few questions

The breather on the left rocker cover, mine is blocked off so I have removed it today and will put a proper filter on it tomorrow but if this was making a difference, I would have thought the idle speed would have increased when I removed it. Is this true? Can this air inlet being closed off really be the reason for my poor economy??

The exhaust has a leak I think because if I hold my hand over the end of the exhaust, the engine note doesnt change and I can hear something exiting from somewhere, could this be the cause of the poor fuel econmony? (I cant think how it would affect it so much)

The car seems to have little power below about 3500 rpm. I have to really put my foot down to make it go anywhere quick, is this an idication something is wrong? My throttle pot gets from 0.325 to 3.7v on full throttle. I am going to sor tthis out tomorrow

The spark plugs are a little black but not really really bad but I am sure this poor economy must be to do with richeness of runinng as I cant find a fuel leak anywhere!!!

Any ideas welcome as I am starting to feel the pinch on the fuel bill a little!

Also, if anyone knows a garage who can really help with this in scotland, please can you let me have their number!

Regards

Chris

Worn out camshaft maybe?

I dont think so, the previous owner put a new engine in which had only done about 2000 miles before I bought it (done another 1500 miles now). It was a new engine, not reconditioned so should be OK.

It is Fred Marriots old car, apparently he managed to get hold of a new engine which was found, still in the original shipping crate so he put it in the car - that was a long time ago before it was not used too much.

I have noticed a rattle when it first starts for 10 seconds - I would describe it as a tappet rattle but dont know if this is possible with hydraulic tappets (dont really understand the system) but this noise soon goes. Oil pressure builds up well and it hasnt used a drop of oil yet.

Thanks for the comment though

Try the easy options first ie air filter plugs leads etc etc or a good tune up mate or as Chris said it may be a worn cam it may be a new engine BUT was it run in properly ie was the cam lubed etc etc I used to get 25mpg@70mph on motorway or should that be slowtorway out of my VPDP EFI AUTO which i would think is the norm. Tappet rattle very common in RV8 engine ie worn cam or tappets bleeding down due to cheap oil or neglected oil changes. Ie engine starting to sludge up and starve oil galleries rockers shafts tappets and yes cam. Remove the oil filler cap and have a look down there with a torch if lightly browned and varnished rockers an shaft ok if all BLACK crusty sludge bad news sorry

Thanks, I will check for "sludge". Ihave changed leads, plugs, air fitler, dizzy cap and rotor and it has had an oil and filter change 1500 miles ago.

How do I check if the cam is worn - I have no idea how the engine was run in.

Thanks

Chris

Your comment about 25mpg at 70 mpg gives me hope! I was getting 20mpg at a steady 20mpg so I am not chasing much!

obviously I meant 20mpg at 70mph, its the wine that wrote that.

To check the cam is worn is to remove it but a good indication is a constant tapping at all revs but having said that it could still be a leaking or worn tappet/s Do the easy options first if i were you as i said it might just need a filter,oil,plugs change and good tune up but the choice is yours mate best of luck

YOu mention a good tune up, is there any thing to tune? As the car is EFI, the only thing i thought could be changed is the timing what else can be adjusted (apart from tickover richness)

Ta

Chris

Hi Chris
Take it to a garage that has a proper diagnostics for your car unfortunatly well fortunatly for me i know a friend whos name is V8 and his last name is 3.9,4.4,4.6,5.0 efi zf etc etc. But as i said he is MY mate and unless you live in or around Brum i can only give you my limited experience and advice other than previous previous you could double your mpg instantly=LPG it

Hello Briggsy, Observations in Red.

briggy2007 wrote:

Hi all, I am running out of ideas on this one. I am only getting around 13mpg from my 3500 EFI auto. I am driving gently but cant get it to increase. I am not using the computer to give me the MPG, I am working it out and have confirmed the speedo mileage is correct. Having worked through Ramons guide, I have a few questions The breather on the left rocker cover, mine is blocked off so I have removed it today and will put a proper filter on it tomorrow but if this was making a difference, I would have thought the idle speed would have increased when I removed it. Is this true? Can this air inlet being closed off really be the reason for my poor economy?? That Breather hole should be approx 40 thou hole (0.040") and if its blocked the crankcase ventilation system will not work correctly. If the input to plenum is blocked due to crud in the breather gallery - ditto. My Efi manual explains fully. Would it make a diff to MPG? - probably yes! There would be a tendency to negative pressure in the crankcase and a consequent reduction or total loss of scavenging by the suction from the plenum chamber vacuum. So the constant amount of air normally going thro the breather system would be less so the eventual engine mixture would be a bit richer. The exhaust has a leak I think because if I hold my hand over the end of the exhaust, the engine note doesnt change and I can hear something exiting from somewhere, could this be the cause of the poor fuel econmony? (I cant think how it would affect it so much) A leak will upset the pressure of gasses in the exhaust and allow air into the system so the orderly extraction of gasses which is influenced by the fluctuating gas pressures would be inhibited. It would certainly upset performance therefor, MPG. Read this for a full explanation of how those pressure changes work Only registered users can see links on this forum! Register or Login on forum! The car seems to have little power below about 3500 rpm. I have to really put my foot down to make it go anywhere quick, is this an idication something is wrong? My throttle pot gets from 0.325 to 3.7v on full throttle. I am going to sor tthis out tomorrow Putting foot down is anti MPG bigtime. The general concensus now is that 3.7 volts would be OK but the voltage changes MUST be smooth, not erratic, otherwise it will kill MPG due to unwanted acceleration enrichment when cruising. The spark plugs are a little black but not really really bad but I am sure this poor economy must be to do with richeness of runinng as I cant find a fuel leak anywhere!!! Black plugs = rich mixture. A bad sign.

In summary there would appear to be several things still need sorting out - so until the whole thing is tickety-boo, expect sub-par performance.

For the record, my own VDP Efi never got better than 19-20 mpg in urban work and 23-24 on long runs.

My TP Vitesse is typically 22-23 urban and 30-33 long runs. due to combined effect of reduced drag, manual box, better Efi efficiency and axle ratio.

My point is, The VDP was in good shape and working correctly, so your identified and unidentified problems are going to make things worse than 19-20 mpg.

As a general observation, all you can really do, is continue to work throught all the Air, fuel, and mechanical/electrical component tests and processes in my Operations Manual, with particular emphasis on Air leaks, the primary cause of Efi Issues.

For enhanced component explanations - go to the website.

Cheers people!

I am just on my way to get the exhaust sealed, go speak to the auto electrician, buy a small filter for the rocker breather and of course, fill up with petrol!

Thanks for the advice!

Chris

I havent noticed any effect on the gasmileage on my cars with the exhaust leaking. So Im thinking your problem is something else than the exhaust.

Mr Lehto!

I think I will leave it as well for the time being, the guy at the local garage has worried me a bit by saying that the manifold studs are a pig for breaking and mine is leaking between the manifold and the down pipes. I have ordered the gaskets anyway and might try this after I have tried everything else!

Ta Chris