Fuel Starvation? Fuel Filters? Atmo.....

Just got back after taking the Alpine on a 2000mile holiday round Europe. Car was great, hardly a murmur and best fuel consumption was measured at 32mpg, although it probably averaged about 29odd. Not bad for a 22 year old car!
Only problem was after 1000 miles without a glitch, it cut out a few times under extreme load, usually whilst accelerating up hill at high speed. The car would start juddering and was obviously not getting enough fuel to it, because after say 10-20 seconds it would then get some more fuel and be ok for a bit. I figured the fuel filters, are there 2? were probably getting blocked.
Where is the first fuel filter located? is it in the front of the car near the fuel tank? I can't seem to see it. I have a replacement and it is quite large it seems but sure this is the correct filter as I got it looked up on my local Motor spares shop computer. Is the second filter in the engine bay to the right? This seems a smaller one and has two outputs, one to each carb I presume. Also could it be possible that the fuel pump is malfuntioning under load? I am more likely to think it is the filters.

It became a little worse the problem gradually and figured it was because the filters were getting more and more blocked. I seemed to get round it by feeding a little air backwards down the fuel line and it seemed to clear the blockage for a 100 miles or so and then it would start again.

I think I would go for the Filters as causing the problem and will change them as I think they havent been changed in the 7 years or so we have owned.
Any other comments/ experience of this type problem appreciated ....

I had this exact same problem on my very first atmo GTA and it was simply the front fuel pump.

The 3 pin connector on the side of the unit has 12v, Earth, and the pulses.The pulses are sent to the computer, and together with the pulses from the flywheel sensor calculate the mpg etc..

Hi

I don't think it would use the flywheel sensor to calulate MPG as this has no reference against MPG, as its simply distance travelled against fuel used. The crank sensor on the atmo is just wired to the diagnostic plug so you can check timing/rpm on a diagnostic unit.

Hi David
Glad to see you are paying attention!!! yes of course you are right, the sensor refered to in my discription should have read " Speed sensor" which is located on the side of the gearbox. Lets put it dowm to a senior moment shall we!!! However is not the flywheel sensor (located on the bell housing about 10 o'clock viewed from the rear) used to drive the rev counter as its primary function? Regards JohnC

Hi David
Glad to see you are paying attention!!! yes of course you are right, the sensor refered to in my discription should have read " Speed sensor" which is located on the side of the gearbox. Lets put it dowm to a senior moment shall we!!! However is not the flywheel sensor (located on the bell housing about 10 o'clock viewed from the rear) used to drive the rev counter as its primary function? Regards JohnC

Nup, that comes from the ignition unit/dizzy.

Yep, right again David, I should have refered to my manual before going to print instead of relying on my memory, especially at my age!!! Yes the feed for the rev counter does come from the ignition circuit, as you said. According to my manuals electrical circuits page 3, it does in fact come off the ignition coil passes through connector R167 then R5 thenR173 and into pin 1 of the 15pin plug which goes into the back of the rev/speedo instrument panel. Thanks for reminding me.

well, its all somewhat above me but I absorbed some of it, thanks alot.... nice to be a part of something where other members seem to know one hell of alot..... much appreciated indeed.......

Well, weird the problem, changed the Fuel filter, which in fact was a tiny looking unit that is fitted to 1 litre cars and infact we haven't changed this for seven years So I put a new bigger one on.

No probs so far but to be honest haven't used it much too test but so far ok... guess I just gotta test it a little more, problem is that U.K roads don't let you go fast enough to make the problem necessarily show again.... Seems a great car with little problems and always has, just don't really use it enough.....

Maybe I am jumping the gun in my ignorance( and learning also it must be added),

I think you would tell me to change the front fuel pump as well? seems logical?
How much are they? Only seemed a small unit, infact was surprised how small.....

thanks again any more advice appreciated

Maybe I am jumping the gun in my ignorance( and learning also it must be added),

I think you would tell me to change the front fuel pump as well? seems logical?
How much are they? Only seemed a small unit, infact was surprised how small.....

thanks again any more advice appreciated

Hi

Yes, re. my post at the top. I had the same problem on a car and it was pump related.

If they're still available they are not too cheap. Steve Dell might have one for sale. I used a Facet racing pump on my own car. Noisy but better.

It might be worth considering the fuel pump relay. When I Bought my atmo in 1990 new, I was concerned about the pump failing, but was informed by the renault dealer that it was more likely to be the relay than the pump,this system was used in other renaults, and was a common fault. For info the relay is operated by a small circuit inside the relay which detects the pulses from the iginition coil and operates the relay,which in turn supplies 12volts to the pump. The theory behind this, is that if you have a bad accident,and the engin stops, the pump will stop, thus reducing thr risk of a fuel fire. I have done a mod by using one of the spare switches on the dash to bypass the relay should the relay malfunction. The switch also has a secondary function, that is to prime the carb before starting if I have not used the car for some time. If I dont prime, on starting the car will fire then stop, due to lack of fuel in the float chamber. Anyone wanting info on mod, will be welcome to it, but it does require a certain degree of electronic knowledge to install.

Yes thankyou again to you both.

Yes John, I too suffer the same (problem) it seems on starting the car. It fires, then stops. Next time it fires and runs fine. Just that initial cold start doesn't quite make it. Probably because of the details you supply/ priming etc. Well, I am no elecrical expert and basic use of a soldering iron and a multimeter is enough for me! I can live with this but interesting to know exactly what goes on. Interesting to see how much some people look after/ into their cars?

Maybe off subject somewhat but relevant also (fuel system/ carbs) ATMO

The first single carb, am I right in saying the mixture screw turned IN weakens the mixture and on the doubles (assuming standard SOLEX's that is) the two mixture screws turned in richens the mixture. [/b]
I have been setting them up for a while and achieved 30+mpg on a run (as much as 32 even) and lovely handling, very nice performance /plug colour. Very clean booming acceleration at 120km+.

Have found that the somewhat ideal/ correct mix is the single carb likes its mixture screw turned in almost totally and the same for the doubles.... even though they do opposites (weak/ rich)...

Am I right in my finding as I figured I can't be far out judging by the plug colour etc? It took me along while to get this...
The old 'myth' of the screws being turned 1 and a half turns out don't think applies too much here!!?

Any advice appreciated again on this carb setup as I think I have got it good but probably don't know as much as others..... still very happy that I got it as good as I have!

Just another point before replacing a pump, it is worth checking the voltage across pump before removing, as if there is a corroded connector, poor relay contact, or loose connection on pump, low voltage will cause the pump to rotate slower, and as a consequence there will be a low delivery of fuel hence fuel starvation at high speed. What I would dos is:- front wheeles up on ramps (hand brake on hard and rear wheels chocked) Unscrew bumper extention to expose pump, start engin, touch meter probes across pump stud TIPS without touching wire connections, take reading, which should be a solid 12volts or more.If it isnt, there is a poor connection somewhere. Whilst still under car wiggle the wire connections to the pump, if they are corroded or loose, the voltage could rise due to disturbing them, if this happens there is your prob. On turbos there is also a connector close to the pump, this should be disconnected and reconnected a few times to scratch away any surface corrosion, then spray with WD40 shaking away excess before tigtening the female sockets of the connector, then reconnect, clean and remake the wire connections to the pump. If voltage improves try car again before replacing pump. My understanding is that these pumps are very robust as all bearings and commutator are running immersed in fuel which acts as a lubercant and cleaner. Note that a 0.6volt reduction in supply voltage to pump equates to a 5% reduction in fuel flow. The joke is that one might replace the pump and say "its fine now" when in fact just remaking the pump connections could have cleared the fault, and they may have just thrown a perfectly good pump!!!
With regard to your carbs, having lived with fixed jet carbs for more years than I care to remember, I have always set the mixture for max revs with engin hot at idle, usually turning the idle speed down when changes in peak revs are more noticable, then returning it to normal idle speed once set. The solex carb is good for this as there is a very large adjustment screw half way up the carb, its forte is that it adjusts the idle speed without altering the mixture. The other adjustments on the twin barrel section according to my manual are factory set and do not require adjustment. As such I have never touched them, so I cant help you there. In general there is very little you can do to fixed jet carbs to improve them, they have been designed to work just as they come. Unless someone knows different!!. I hope the above info is of interest and help to you. regards John

Not only that, on the Turbo the connector AND the suppressor cause problems, I have seen over 4 volts lost through them. Cut them both out, and have direct wiring going to the pump terminals.

Its not just voltage too. Current draw. You can have 12v at the pump, but when it comes on load (turbo only) and the fuel pressure increases with boost then then the wiring can't keep up with current demand.

Carbs....without proper testing equipment, the easiest and best solution is just to take the car to a carb expert/rolling road that can set them up for you in running conditions.

Just for info, I was passing my fiendly Renault garage this morning (not that difficult on an island 12 x 5) so popped in to check on availability of above. Pumps are available via renault from France at £241 that is for atmo, dont know about turbo, but filters are available at £15.13,and are the same for both atmo and turbo.needless to say I orderd one to keep as a spare just in case they become unavailable.In fact I have never changed it, and car is now 18 years old. In the next few days I will post the manual priming mod come fuel relay bypass which I find invaluable for 1st time starting. It would be interesting to know if anyone else has the same two key turn starting prob as we do, also did any one else have an after purchase mod fitted by Renault Tec which involved pumping fuel from tank through all pipe work to carb and back for 40mins after stopping the engin, in order to cool carb and prime for next start, Never liked it riped it out in favour of my own mod. Fortunately it was done foc. but I did gain a fuel pump which was used in the mod which appears to be the same as the one used in the car. I keep it wrapped up in a box under the bonnet just in case. Even if it isnt it will get me home, hopefully!!! but it is the same shape, size and pipe conections.

Just for info, I was passing my fiendly Renault garage this morning (not that difficult on an island 12 x 5) so popped in to check on availability of above. Pumps are available via renault from France at £241 that is for atmo, .

Extortianate!

This is the pump I used. Think it was the SS503. Made nigh on 180bhp on an atmo.

http://www.fuelsystem.co.uk/web-facet.pdf

Only downside is its loud clicking on running.

What would be suitable to replace the front pump on a turbo