Results of my fuel pressure tests - any advice? [long]

Ok, it finally stopped raining / snowing for long enough to allow me to get out and test my system using Wellsy's very nifty pressure test gauge setup   . to read about my cold start woes see the other threads on the symptoms. Basically the car starts from cold runs for a few mins and then dies and will not restart as it warms up.

Apologies, but advance warning this is going to be a long post, so here goes, test numbered for easy reference later.

1. Fuel pump delivery test.
Made up a small "jumper" wire with blade fuse holder and wire from Halfords and stuck a 10Amp fuse in it. I removed the fuel pipe from the fuel filter closest to the front of the car and stuck it in a 1.5 litre bottle. Haynes is spectacularly unclear in identifying the two slots on the fuse realy panel you need to short, citing L13 & L14 which bore no resemblance to anything on my Campaign relay or fuse panel. Luckily this link came to the rescue from someone else on the forum:

http://www.auto-solve.com/mech_inj.htm#MFI04

Its basically the two large slots corresponding to the two largest "blades" on the relay. On my relay they were labelled the same as in the article - namely pins 30 and 87.
Use the home made jumper to short those on the fuse box for 30 secs and no more. Usually helps to have an assistant to do this.

RESULT: My fuel pump delivered more than the minimum 1 litre in the 30 second interval, so hopefully the pump is OK

2. COLD control pressure test.
Test gauge connected with tap open, aux air valve and warm up reg eleccy connections disconnected as per Haynes (19.7).
Ambient temp was only about 6 deg C, so a bit colder than recommended. My readings were 27psi, which is way higher than the acceptable range (14-20psi @ 10 degC)   .

RESULT: Haynes suggests further system checks, possible return line blockage, but also warm up reg suspect.

3. System pressure test (Haynes 19.5).
Once engine had warmed up with cold start air valve and warm up reg eleccy connections still disconnected. This was not ideal, but the only way I could get the engine to run to full operating temp.
The system pressure with the test gauge valve closed was around the 75psi mark, engine running at about 2000rpm. This was within the 65-75psi range listed in the Haynes, although I don't know whether the reading would be significantly affected by the disconnected air and warm up reg connections?

RESULT: Looks OK at 75 psi?

4.HOT control pressure test (Haynes 19.8)
Hard to get this one properly as the engine dies almost immediately after starting with the cold air reg and warm up reg connectors back on. The brief reading on the test gauge with the tap open I get is 49 psi, which just scrapes into the recommended 49-57 psi in the Haynes.
Like I say though the engine only runs for a few seconds like this.

RESULT: Marginal pass at 49psi… sortof.

5.whole system pressure test (Haynes 19.9)
Test gauge with tap open, warm up reg and cold air reg connected. Engine warm. This test is to check the residual pressure after 10 mins. Again car only starts briefly and gauge reads 49psi then engine stops and pressure drops immediatly to about 40 psi.
After 10 mins the gauge reads about 38psi. Haynes says as long as it reads greater than 27psi no further testing needed, so OK on that one I think.

RESULT: Residual pressure after 10 mins 38psi, which seems high, but OK.

GENERAL OBSERVATIONS:
First time I have run the car from cold with eleccy connector off BOTH the warm up reg and the cold air valve. This resulted in the car idling at about 2000rpm, but it didn't stall and was able to run to full operating temp and fan cut in.

Although I did replace the warm up reg with another second hand one, I have no guarantee it was OK. The tests seem to point towards that being defective, but I can't be sure.

A few people have also mentioned the non return valve in the fuel pump - is it possible to test this in situ or does it have to be removed?

Any suggestions / help on this appreciated. Wellsy has kindly offered me some working spares for testing which I might take him up on, but I would welcome any other suggestions. I don't have a lot of money to throw at this so don't want to replace expensive items like warm up regs and metering heads unless there is a fair degree of certainty thay are faulty.

Also can't afford a Bosch tune up visit right now (not that the car would get there anyway in its present state!!).

Cheers,

Chris

Chris,

For me the key test is the warm control pressure which is at the top end of the limit.  Higher control pressure means leaner mixture.

Your tests show a high cold pressure and warm pressure at the high end.  This could be caused by these things according to my book:

"Restriction in CPR return line
Defective CPR

To distinguish between these allow the CPR return to flow into a container.  If the pressure drops the fault is with the return line.  If it does not drop then it is the CPR"

I'm not convinced by the logic here though  :? .

One thing to do is get the exhaust gas analysed to see if the problem is a weak or rich mixture.  Might be difficult if you can't get the car there!  Is there a gunson cheapo equivalent?  What about gunson's colour tune i've used this effectivly in the past.

I'd also go through all the vacuum pipes to cehck for any leaks or if any are collapsing under vaccum.

Did you say you could get the car hot running by disconnecting the warm up reg and air bypass valve electrical connections?  Does that give some clues?

Cheers

Rich

Hi Rich,

So just to make sure I am on the right lines here, CPR = control pressure reg = what I have called the warm up reg. Yes?

If so am I right in thinking you are suggesting disconnecting the other fuel line from the warm up reg, (i.e. the one NOT connected to the test gauge) and sticking that in a bottle.

Won't I need to blank off the hole on the metering head it has come out of too?

And you are saying if the pressure readings with this pipe disconnected are OK then its a restriction in the return line, if no change then it confirms the warm up reg is at fault?

Sorry about all the questions, but this whole fuel diagnosis thing is doing my head in!! If I had access to some known good components then I could probably eliminate a lot of potentials quite quickly by swapping out.

I still feel its the warm up reg - I think the replacement one may have been a duffer too.

What about the fuel pump check valve I mentioned - any way of testing this easily?

Thanks,

Chris

Yes CPR is warm up reg.

Not sure about blanking return connection on metering head.  i guess you'd need to do that.  Onther way would be to remove both lines and see if you can easily blow through them.

What the book is saying is that one of these two things is defective - either return line or CPR.  The test identifies which one.

Give me a call if you want to chat through this some more - I am around this afternoon.

Cheers

Rich

Ok, so, car runs at 2000 rpm with CPR( warm up reg) and aux air valve dissconnected right?

How about just reconnecting the aux air valve? that should bring the revs down a bit and get the engine to tick over a bit slower.

Anyway, sounds like you have made some progress, at least you can get the car to run now!

Peter.

Rich - sorry I missed your post yesterday. I'll try blowing through the return line and see if there appears to be any blockage.

Pete - I'll try reconnecting the cold air valve on its own. Even with the warmup reg (CPR) disconnected, it eventually warms up from the engine block heat, but as you say at least it runs for more than a few minutes!!

Any tips on disconnecting the return line at the tank end. Unfortunately I still have about half a tank of optimax in there and I don't want it p*ssing out all over me and the driveway when I disconnect the return  8O

Or does it not work like that? Will have to check the Haynes for procedure I guess.

Really hope the return line hasn't collapsed as its a PITA job to do and I am skint at the mo   . The fuel lines are original and a bit corroded in places so its not beyond the realms of possibility I guess.

Determined to diagnose this before spending out anything though - a good test of my spannering skills!

Chris

Chris,

I mean the return line from the warm up regulator not the tank return.

Cheers

Rich

Ah OK - sorry, got the wrong end of the stick there. That should be easy enough to check for blockages.

Probably wouldn't do any harm to remove the metering head and blow though with compressed air as well - just to check there is no crud lurking in there.

Will try and do this today.

Cheers,

Chris

Well I THINK I finally got the car going, although I think I may have messed up the idle mixture as its not idling quite as it should.

I think this was a combination of factors as I also finally ended up fitting a brand new coil, set of HT leads, dizzy cap and rotor arm and spark plugs - plus of course a spare warm up reg that Rich kindly lent me for diagnostics.

I need to get the colortune on there to reset the idle mixture screw. but I hope I've cracked it now. The pressure readings for the loan warm up reg were within spec so I guess I need a replcement one of those for starters. I know I could get a secondhand one again, but believe me I don't want to be fannying around with this again. I think the extra cost for a GSF one is probably worth the peace of mind even though I am skint at the mo!

The one thing that I have learnt from this is try to eliminate as much as possible from the equation before trying to diagnose the problem I initially held off putting on the new electrical stuff as I didn't want to introduce new variables into the equation. This was a mistake as I should have fitted all the new stuff to eliminate it as a potential source of problems.

It seems I was probably suffering from a combination of problems, namely a knackered warm up reg combined with (probably) a dodgy coil/ HT leads.

The car could of course prove me completely wrong by dying on me again, but hopefully I have found and isolated the problem.

I have to say though that a fuel pressure gauge is an absolute must for diagnosing this kind of problem - Haynes is right, without it its just pure guesswork. Since getting Wellsy's gauge I now have one of my own and it will be taking pride of place in my Mk1 toolbox for any future fuel issues.

Has anyone got any experience of the GSF warm up reg? Its significantly cheaper than the Bosch one from ECP (about ?115 vs ?175). Are the GSF ones just reconditioned Bosch ones anyway?

Need to get the car sorted for its MOT in about a month and a half and I suspect a fair few bits need doing. Have a few small rust patches, but hoping these will not be MOT failures. Also need to sort a blow on the exhaust, but hopefully this should be a million times easier now I have my manual 4 poster ramp setup in the garage  8)

Chris

Got any pics of your 4-poster Chris, would be good to see!

(Bet it wasn't the 4-poster the missus was hoping for!)

Will try and take some pics today Hairy. Bit concerned after all this I won't be able to get the car onto the ramp in the damn garage  8O .

Currently have a very heavy engine and gearbox that need to be fitted onto an engine stand so I can move them out of the way - thats the job for today  

ChrisB said

Haynes is spectacularly unclear in identifying the two slots on the fuse realy panel you need to short, citing L13 & L14 which bore no resemblance to anything on my Campaign relay or fuse panel.

Are these any good??

Nice pics prowler - those are the very same ones  :wink: .

As I say you can be doubly sure, by checking the numbers printed on the underside of the relay for the terminals and that like I posted previously.

Just realised I don't have the piggin bolts that bolt the gearbox onto the engine, so I can't put it onto the newly assembled engine stand - damn  :x

Don't suppose anyone has any spare do they?

Chris