Hard Stumbling Start- Where to start? Topic is solved

[Zeeko]

Hey all-

I think I've encountered my first issue with my newly acquired 2004 V70 2.5T with ~ 153000 miles.

Hard start- the car will crank every time and sound like it will start fine, but will very often sputter and die when I let go of the key when a normal person lets go of the key. If I hold it extra long- a little longer than normal- it will sometimes start okay. On second start, it always starts fine. No check engine lights.

The issue happens in the hot, warm and cold, but as winter has commenced, the problem has seemingly gotten worse. I'm not 100% sure where to begin- I've read quite a few cases of this- many of which seem to happen with 2004's.

I'm going to list a couple potential culprits I've found while searching, but I would be grateful for any words of widsom. Additionally, I do have a volvo vida/dice unit if anyone has suggestions on things to check...

Possible culprits:

1. fuel delivery- Fuel pressure sensor/pump? I will say that I have the made in belgium volvo that has the in-tank pump and filter, however, it has been changed at the dealership around 107K miles.

2. immobilizer antenna- i personally don't think this is the issue as it cranks fine every time, but I don't know what a bad key would actually do if used- if the car would crank fine but not start, etc.

3. Coolant temperature sensor- I've read that this part failing will cause the car to not know if the coolant is hot or cold when starting and can lead to issues... I will say that my gauge seems to be about 1/16" on the cold side after I've driven the car for quite some time and doesn't really ever hit perfectly straight vertical.

4. Spark/Coils- I just changed all of the plugs and coils and it didn't help / hurt the issue

Any thoughts?

[precopster]

Eventually it will code......my 2001 V70 T5 with 143k miles took about 1,000kms before it eventually coded with a faulty O2 sensor and with similar symptoms. It's such a guessing game with these and unfortunately your list only contains about a third of the possible culprits.

I'm more than just a little concerned about the temp gauge not reaching middle.

[Zeeko]

me too. I wonder if would be worth warming up the car as much as possible and then hooking up the vida unit to see what it's spitting out for temp.

[precopster]

It should range between approximately 88 and 105 Celsius when warm depending on ambient temps and load before measurement. Leave a/c off as the cooling fan will throw temps down. Between the above temperatures the needle should be in the middle. Fan comes on at 105 degC however it may not reach this in Autumn unless it's driven.

If temps don't reach the ranges above after a drive I would suspect a faulty thermostat. In your case it is integral with the sensor and not too hard too replace (though it's definitely a fiddly job requiring the right tools.

[oragex]

Without a code you are only in the guessing area, perhaps better not to replace parts too quickly, The new pump is a little suspect as these pumps very very rarely fail (althought less knowledgeable garages will replace them as a matter of habit). Is it sure the pump was replaced by a main Volvo dealer? Related to fuel delivery issues for these cars were the FPS and the PEM.

[93SCMax]

Are you sure your battery is up to snuff? You say it's gotten worse with the colder weather. The CCA (cold cranking amps) may not be enough to fire her off the 1st time, or needs more time. If you have another car with a similar battery post set-up, try exchanging the batteries and see if it improved. Also double check that your multi belt is not worn or slipping. If your alternator isn't spinning properly, that could contribute to a hard start.
I would also discount the fuel pump. Coolant temperature sensor would be my next target. I always put in a new one, and a new thermostat, when I change the coolant. If your's is original, it's overdue.
Good luck.

[Zeeko]

All right update-

The old battery was from 2012 and 600 CCA so I replaced it with an 800ish CCA... No change. However, I popped my obdII module on and went for a drive while monitoring- the coolant temp drops from about 80-90ish in stop and go to around 75-76 on the highway. It's about 30 degrees here. Is this bad? I also noticed the cat has been replaced in the past 50K miles...

@oragex- the pump was definitely replaced by the volvo dealer in town and i know they do good work/used Volvo parts.

[93SCMax]

I don't have any background concerning the coolant temperature drops, but that seems low on the highway. I'd expect pretty consistent temperature once the thermostat opens.
If your catalytic converter has been replaced, I'd want to know if the O2 sensors have also been replaced. Replacing the cats is unusual.
I'd change out the coolant temperature sensor and eliminate that as a possible source. Make sure you purge any air from the system. May want to look at your O2 sensors if the coolant temp sensor doesn't cure your conditions. Still surprised you haven't thrown a code.

[Zeeko]

Solved the starting issue- I switch to 91 octane (had been using 89 since buying the car about a month ago) and the problem cleared right up. I've had zero stumbling starting issues. I will be popping in a new thermostat to address the low temp issue though (that's another story).

[93SCMax]

Congratulations on the cheap fix. Glad you resolved your issue and posted the solution.
Others on this forum (with turbos) claim they run low test gas and don't have issues. My owners manual states minimum 91 octane and the only time in 16 years I ran low test, I had issues.