Open Road

Hey guys, I'm looking for opinions with this one.
After an extended dyno session, warm day, my fuel pump was making more noise. I would state same type of noise, but louder.
Performance was unchanged, but obviously I need to chase this.
I will look at usual suspects, but it occurred to me that I read about fuel pumps making more noise with hot fuel. Can this be true? Cavitation? Pre-vapor lock?
The tank was 3/4 full, so level was not low at all.

The stock fuel cooler is essentially inert since I have deleted the a/c.
This is another angle I did not appreciate ahead of time.
Running a stock fuel pump, based on mathematics with the low boost SC, I didn't see the need to upgrade to a Bosch 044 pump, but i could certainly add an inline cooler without a lot of effort.
Thanks.

My opinion…meh.

Vapor lock is caused by high-pressure fuel vapor displacing fuel in the fuel rails back to the fuel pump which then can’t generate fluid pressure due to fast system pressure drop after shutting off the engine.

In a running engine vapor lock can’t really happen and cavitation shouldn’t be an issue provided you’re using ‘good’ summer gasoline that has anti-foaming agents as part of the additive package.

Now, if perhaps, it is hot, the tank is 1/8 full and you’re on a dyno then maybe you’ll get some foamy gas.

Alternatively… when was the last time you look at the tank strainer? Or at how much sediment was at the bottom of the tank? Fuel filter age?

I’d chase the obvious first…

Ok.
Deeper dive.
With sender out, the strainer looks reasonable but I’m going to replace it while I’m in there.
Thoughts on diaphragm? I assume it’s to stabilize sender. Looks like I tore it removing sender, assuming not a big deal.

Ok now I’m finding threads about this obscure swirl pot.
What’s my move?

Crumpler wrote: ↑Sat Apr 22, 2023 12:01 pm Ok now I’m finding threads about this obscure swirl pot.
What’s my move?

You pulled the strainer and it appears to be in good shape. I can’t tell if the bowl is clean of debris.

Thanks for following Dave.
It’s all good except for this crack/tear on the lid of this swirl pot thing. If lid secure on pot am I good to go?

Crumpler wrote: ↑Sat Apr 22, 2023 6:19 pm If lid secure on pot am I good to go?

Yes.

Change your fuel filter if it’s old-ish.

Reverse polarity your fuel pump and back-flush any crap.

Check your lines from filter to engine bay for damage/crushed/pinched spots.

Thanks man!

Side note.
Replacing fuel line from filter to hard line in rear fender.
Never heard of one failing. I assume because no real heat cycles like in engine, but it’s pressured and 37 years old right?

Crumpler wrote: ↑Mon Apr 24, 2023 9:26 am Never heard of one failing. I assume because no real heat cycles like in engine, but it’s pressured and 37 years old right?

That’s pretty much my logic at this point: 28 to 46 years old. So, if I’m “there” it goes.

Um, I don’t plan on being up side down, but what about this check valve coming off the linear expansion tank? Anti-roll valve some one said once.
Replace? I would expect any check valve to be shot by now, pessimistic?

Crumpler wrote: ↑Mon Apr 24, 2023 10:45 am Um, I don’t plan on being up side down, but what about this check valve coming off the linear expansion tank? Anti-roll valve some one said once.
Replace? I would expect any check valve to be shot by now, pessimistic?

Should be easy enough to test. IIRC, it’s a stainless ball bearing in a sleeve. Russian engineering not German engineering. (i.e. doesn’t work very well, but is hard to kill.)

New fuel pump, filter, strainer, sender, fuel line, and r/r cradle. Going jump fp relay in the am and confirm no leaks and normal pressure on the rail.

Hello everyone from Madrid, I am the happy owner of an 87 5 speed S4, I just registered since I found it to be a very interesting forum from which to learn a lot, I came across this thread and exactly the same thing happens to my car, too I had considered installing a fuel cooler but I have a doubt about which one and how to install it. I imagine that on the return line, I would appreciate opinions and a solution to the problem, thanks in advance.

javiherdepa wrote: ↑Thu Dec 07, 2023 6:50 pm Hello everyone from Madrid, I am the happy owner of an 87 5 speed S4, I just registered since I found it to be a very interesting forum from which to learn a lot, I came across this thread and exactly the same thing happens to my car, too I had considered installing a fuel cooler but I have a doubt about which one and how to install it. I imagine that on the return line, I would appreciate opinions and a solution to the problem, thanks in advance.

Why do you think you need an additional fuel cooler? You already have one you know, right?

Yes, it has the original fuel cooler, but just like what happened to my partner, my S4 had the air conditioning removed and I would like to see an alternative to the fuel cooler for the air conditioning system.

It should be said that both the pump, internal tank filter, external filter etc etc etc were put in new ones as well as an internal cleaning of the tank, the polarity change of the pump was also done but it was of no use, that's why my interest in the Possible installation of an extra fuel cooler.

My s4

javiherdepa wrote: ↑Fri Dec 08, 2023 8:17 am … but just like what happened to my partner, my S4 had the air conditioning removed and I would like to see an alternative to the fuel cooler for the air conditioning system.

Ok. But *what symptoms* do you encounter that make you think you need one?

Millions of cars don’t have a fuel cooler and get by just fine.

Well, just like the colleague in circumstances of, for example, passing the annual technical inspection here called ITV in which a lot of time is spent waiting with the vehicle started, there comes a time when, due to the heat generated, the fuel pump begins to hum and The engine has an unstable idle, which under normal circumstances does not occur.

Have you done a fuel pressure leak-down test?

of course, correct fuel pressure values ​​both with the engine started and stopped after more than 30 minutes, pressure regulator, imposed shock absorbers etc etc etc all new, the problem appears in the conditions mentioned in my previous message and when not Provide the car with an air conditioning system by which the fuel is cooled when it returns to the tank.

Since my replacement of the fuel pump, I have not heard any humming. I have not had any dyno testing since, but I have had several track days in moderate heat.

Glad to hear we have a kindred spirit in Spain.
Beautiful country. And I remember pretty impressive Touring roads.

My plan to place a cooler would have been in the return line under the car, one of the in line models.
This was an example:

https://www.speedingparts.com/p/fuelsys ... -48cm.html

Worf is typically right however. ;)
Probably a solution looking for a problem.

Isn't it a bit risky to locate that cooler at the bottom of the vehicle?

Crumpler wrote: ↑Mon Dec 11, 2023 3:41 pm Probably a solution looking for a problem.

Or treating a symptom, not the disease.

javiherdepa wrote: ↑Tue Dec 12, 2023 5:08 pm Isn't it a bit risky to locate that cooler at the bottom of the vehicle?

There are already fuel lines on the bottom. Obviously, though, it might be a good idea to provide a shield for it and to make sure it’s low profile. There *might* be room on the return line where it follows the curve of the rear seat well. I’d need to take a long look at that.

Of course, the very obvious place to put it is on the firewall.

All that written, Crumpler has potentially solved his problem with a new main pump. Note also that his problem was on a dyno, with a supercharger and presumably not in the arctic. Huge power, huge heat soak, no airflow.

I can well understand why a fuel pump might not like that life.

A stock? 928 idling for 30 minutes, stopped, while waiting for inspection? If the pump is audibly distressed by that then I think fuel cooling is treating a symptom. If it’s 43°C outside then, yeah, a fuel cooler will help.

Since your fuel system holds pressure for 30 minutes, then the next data to be reported would be the idling engine coolant temp reported by the TEMP-II sender (NOT gauge sender) and the ambient temperature associated.

If your 928 isn’t stock then you need to give us details.

Yeah, I tend to see only the pressured fuel lines as fire risks.
This was low profile enough that you would hit main frame rails first. But yeah, there is no free lunch, so to speak. ;)
Conservative has not been the mainstay of this particular build.
You should stick with Worf, he will keep you out of trouble.

My s4 has 928motorsport intake spacers installed, ken chips, 24lb injectors, gt intermediates, rmb, bmc air filter, optimized fuel tank outlet with larger diameter, new fuel outlet tank filter, 044 pump (with the original pump also had the same problem).