Slight hesitation upon initial acceleration 2003 V70 Topic is solved

[kallekula]

Did you get it sorted?

[unggthat]

Nope! Only thing left in the fuel system is the pump...possibly it is slightly weak? Other than that, I'm just not sure what's left to look at!

[jonesg]

I'd spend a bit of money on Vida instead of more parts.
Haynes isn't bad but tends to be generalized whereas Vida is specific.
Fuel pressure sensor has to be OEM, the cheapo ones are known to fail right from the box.
From reading here over the yrs , fuel should be 45 lb or 3.10 bar.

Yes, vida will do fuel trim graphing.

[unggthat]

Spent the morning trying to get my VIDA/DICE to work...old computers and sketchy software=no go. I had it working a few years ago but hadn't needed it since and the computer takes 10 minutes to load on a good day...

However:

I'm now almost positive it is the fuel pump/anti-flowback valve. Finally got my identical car to run (transmission replacement and broken wire on the crankshaft position sensor, etc.) and checked fuel pressure readings. My fuel pressure gauge reads a super steady 3.8 bar on that car. On the other one (with this hesitation, etc.): 3.7 with a strange constant wiggle. I think the flowback valve is bad, causing the pressure to constantly be varying and since the pump is constantly cycling, the pressure is doing all kinds of fluctuating. Cold starts have been getting worse--I checked and the rail pressure after an hour was basically gone. So I think I've FINALLY discovered the issue here. Fuel pump arrives tomorrow. Sure, I could just install an inline valve, but at almost 200k miles and only a little over $100, I'll just put in a pump and everything. I'll post back after it goes in!

Noteworthy: These cars both have DENSO engine management. My Haynes manual must be incorrect or else they used different pressure in European cars (it's a euro copy of the manual). US-spec DENSO cars should be 3.8bar, according to my car that has worked perfectly for 7 years.

[abscate]

I think the 2003 mirrors the 2005 spec

Fuel Pressure (Key On Engine On) 375-395 kPa (54.3-57.2 psi)
Fuel Pressure (Key On) After 20 Minutes 200 kPa (29 psi)

[jonesg]

Spent the morning trying to get my VIDA/DICE to work...old computers and sketchy software=no go. I had it working a few years ago but hadn't needed it since and the computer takes 10 minutes to load on a good day...

However:

I'm now almost positive it is the fuel pump/anti-flowback valve. Finally got my identical car to run (transmission replacement and broken wire on the crankshaft position sensor, etc.) and checked fuel pressure readings. My fuel pressure gauge reads a super steady 3.8 bar on that car. On the other one (with this hesitation, etc.): 3.7 with a strange constant wiggle. I think the flowback valve is bad, causing the pressure to constantly be varying and since the pump is constantly cycling, the pressure is doing all kinds of fluctuating. Cold starts have been getting worse--I checked and the rail pressure after an hour was basically gone. So I think I've FINALLY discovered the issue here. Fuel pump arrives tomorrow. Sure, I could just install an inline valve, but at almost 200k miles and only a little over $100, I'll just put in a pump and everything. I'll post back after it goes in!

Noteworthy: These cars both have DENSO engine management. My Haynes manual must be incorrect or else they used different pressure in European cars (it's a euro copy of the manual). US-spec DENSO cars should be 3.8bar, according to my car that has worked perfectly for 7 years.

Vida has probably expired, just reset the expiration date in the registry to 2030.
Yagger has a video showing how to do this in detail, worked for me.

[unggthat]

Ugh, thanks for the tips. I went through all of that (twice now) and it simply stopped loading VIDA--it will say "Starting" indefinitely. Not sure what I did, because it loaded fine before this but just wouldn't log in. If I was smarter on the tech side of things I'm sure I could figure it out...thanks for the tip though.

[unggthat]

Well, well, well. It was the fuel pump. Or fuel filter or anti-flowback valve. Or some combination of the three. I have a metal tank--the whole process was actually quite simple. So now I have an entirely new fuel system! The idle has smoothed out just like every other whiteblock car I've owned. It starts happily. Hesitation gone. Thank you all for the help--this has been a longer saga than I had hoped, but it didn't end up costing TOO much in the end. Have a good weekend, all!

[jonesg]

Thats probably how a mechanic would do the job, renew everything to eliminate returns.

[unggthat]

Well, the plot thickens. So the hesitation upon acceleration is largely gone and the idle is smoothed out mostly. I really thought I had it all going. But it doesn't always start. Kinda grumbles and feels like it might not start, but only sometimes. Usually on a cold engine, but not always. Still no codes, even when it sometimes stalls after starting up and running for a few seconds. Sometimes it'll get going and then die as you start to reverse. Takes a while of cranking to get it back going again.

One complicating factor--did a proper compression test. Engine warm, WOT. All cylinders were at 130. I know this is low...these engines are usually in the 160s-170s, even with high miles. I'm surprised, given that this car had an extensive service history at Bass Auto in PA...

So now I'm wondering if these issues are due to the low compression. Though why would it usually start fine?

This car is totally befuddling me. I've never had a car defeat me so much. And it only has 186k miles! I usually BUY them with more than that!

Not sure if any of you have places to look now--what could cause stallout without any codes?

Thanks!

Nate