Hi superelbert
I tried disconnecting my vacuum line just to see if the pressure stabilised but made no difference (just increased the pressure as expected). I have a new regulator on order, hoping that might change things?
Cheers
DaveZZ
Fuel Pressure Regulator Fault Symptoms
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Read the manual to see if your question is answered there before posting. If you have questions about MS1/Extra or MS2/Extra or other non-B&G code configuration or tuning, please post them at http://www.msextra.com The full forum rules are here: Forum Rules, be sure to read them all regularly.
Read the manual to see if your question is answered there before posting. If you have questions about MS1/Extra or MS2/Extra or other non-B&G code configuration or tuning, please post them at http://www.msextra.com The full forum rules are here: Forum Rules, be sure to read them all regularly.
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superelbert
- MegaSquirt Newbie
- Posts: 15
- Joined: Wed Jun 23, 2004 4:11 am
- Location: Norway
Interresting!
That's a good elimination approach!
Some further investigations have shed some more light on things...
When I noticed these fluctuations it was because I had a look under5 the hood as I thought the fuel pump sounded a bit peculiar...
The engine was then well hot and had been idling for a while..
After starting the car from cold this morning, the neede was rock steady on idle....
In my case, I strongly suspect that a combination of engine and pump motor heat caused vapour bubbles in the fuel system as fuel flow (and surrounding air flow) at some point became innsufficient to provide any cooling.
Now, in my case, this hasn't really resulted in any tuning or idling problems, at least not that I'm aware of.
As a note, I've never vented my fuel circuit, which seems to have worked just fine.
I think what I've found is that under bonnet temperatures are getting a bit high, time to address some cooling issues.
Is your engine compartment getting hot??
if so, you could perhaps use some rags soaked in cold water to cool your fuel circuit down.
That should get rid of any vapour issues if that is the issue..
Some further investigations have shed some more light on things...
When I noticed these fluctuations it was because I had a look under5 the hood as I thought the fuel pump sounded a bit peculiar...
The engine was then well hot and had been idling for a while..
After starting the car from cold this morning, the neede was rock steady on idle....
In my case, I strongly suspect that a combination of engine and pump motor heat caused vapour bubbles in the fuel system as fuel flow (and surrounding air flow) at some point became innsufficient to provide any cooling.
Now, in my case, this hasn't really resulted in any tuning or idling problems, at least not that I'm aware of.
As a note, I've never vented my fuel circuit, which seems to have worked just fine.
I think what I've found is that under bonnet temperatures are getting a bit high, time to address some cooling issues.
Is your engine compartment getting hot??
if so, you could perhaps use some rags soaked in cold water to cool your fuel circuit down.
That should get rid of any vapour issues if that is the issue..
After months of searching for answers, modifying things I didn't know what else to do! I do suffer with heat soak (like lots of other people seem to) but I'm not sure if it has a lot to do with my base problem, some days the fuel pressure seems fairly stable and other days it's not quite so good. Last night I started it after making yet another wiring mod, the fuel pressure I thought was erratic from cold (maybe 8 deg C over here), funny thing was the car seems to run richer and I had to lower the VE in the idle area (didn't go out for a drive). Anyway I have not got a spare FPR and the one I have is non adjustable so I thought it would be useful to lower my pressure (maybe help reduce my fuel hammering) and see how things go.
But your point on fuel getting hot is a good one, in my case I am wondering if I have very small bubbles in my system when it is cold (caused by the FPR as noted in previous posts) being returned to a relatively small OEM surge pot. As the under bonnet temperature rises, heat soak sets in, then these normally small bubbles get bigger due to the heat. This is all a stab in the dark guess, hopefully in the next few days I will have eliminated another possible cause....
Cheers
DaveZZ
But your point on fuel getting hot is a good one, in my case I am wondering if I have very small bubbles in my system when it is cold (caused by the FPR as noted in previous posts) being returned to a relatively small OEM surge pot. As the under bonnet temperature rises, heat soak sets in, then these normally small bubbles get bigger due to the heat. This is all a stab in the dark guess, hopefully in the next few days I will have eliminated another possible cause....
Cheers
DaveZZ
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superelbert
- MegaSquirt Newbie
- Posts: 15
- Joined: Wed Jun 23, 2004 4:11 am
- Location: Norway
bubbles
Hmm.. I nteresting theory about smaller bubbles getting bigger, they probably will tend to to some degree, but there is a limit to how much they will expand, I think serious bubbling will probably have to come from a heat soak where the petrol is evaporating/ boiling conciderably.
Check out this link...
http://www.chevrolet.com.au/articles/petrol.html
As you can see from the diagram, petrol contains a lot of low boiling point hydrocarbons, so it is obvious that high under-bonnet temperatures might generate vapour lock/ ecessive bubbels in the fuel system, even if the pressure is above atmospheric..
Check out this link...
http://www.chevrolet.com.au/articles/petrol.html
As you can see from the diagram, petrol contains a lot of low boiling point hydrocarbons, so it is obvious that high under-bonnet temperatures might generate vapour lock/ ecessive bubbels in the fuel system, even if the pressure is above atmospheric..
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detcollector
- MegaSquirt Newbie
- Posts: 12
- Joined: Tue Oct 26, 2004 3:41 am
- Location: UK
Sounds like a hot fuel problem. A usefull check is to put the return line into the fuel tank filler. Don't forget to blank the return line at the tank though. This atleast identifies a swirl pot + hot fuel issue.
If you are a borderline this can be afected by the amount of fuel in the tank. It also wont be helped by having lots of pumps and filters.
However the main problem would still be excessive heat at the fuel rail.
Large fuel rails make this worse as does an inline fuel rail system on a V8. A ring system is better as it avoids vapour lock at hot spots. Early fuel systems required thermal insulators to try and reduce heat paths to the rail/injectors.
Good luck.
If you are a borderline this can be afected by the amount of fuel in the tank. It also wont be helped by having lots of pumps and filters.
However the main problem would still be excessive heat at the fuel rail.
Large fuel rails make this worse as does an inline fuel rail system on a V8. A ring system is better as it avoids vapour lock at hot spots. Early fuel systems required thermal insulators to try and reduce heat paths to the rail/injectors.
Good luck.
Thanks Guys
Appreciate the input, as fate has it I do have a 3/8NPT port on my filler tube, just need a bit of extra tube + fittings. Sounds like a good week job.
I was going to use a single in tank system except the vehicle I choose to use had a problem with bad connectors leading into the swirl pot so I choose to use the pre-pump since it has a lower current draw. Hind sight is a wonderful thing.....
Cheers
DaveZZ
Appreciate the input, as fate has it I do have a 3/8NPT port on my filler tube, just need a bit of extra tube + fittings. Sounds like a good week job.
I was going to use a single in tank system except the vehicle I choose to use had a problem with bad connectors leading into the swirl pot so I choose to use the pre-pump since it has a lower current draw. Hind sight is a wonderful thing.....
Cheers
DaveZZ