Volvo 460 1.8 Uneven cold idle and lower mileage

[Soren Nielsen]

Volvo 460 1,8 B18U gasoline, single point injection. Year:1995 198000km. Manual transmission.

I could use some opinions on what’s wrong with my car.

The problem occured after I had the gas tank removed in order to replace a leaking brake pipe.

1) When the engine is cold the idle is uneven
2) Hesitates on acceleration when the engine is cold – sometimes it feels like it’s about to die when I attempt to accelerate and I have to declutch to prevent it from dying. It normally helps to rev the engine beyond 2000rpm before slowly releasing the clutch in order to get the vehicle moving.
3) It spits out, what I assume to be, unburned fuel from the tailpipe when the engine is cold (it smells like gasoline and leaves black stains on my white wall)
I haven’t tested if it also spits out gasoline when the engine is warm.
4) Increased fuel consumption from app. 14km/l (33mpg) to 11km/l (26mpg)

1 and 2 resolves themselves after about 1 minute of driving and after that the car runs normal – besides from the increase in fuel consumption.

This is what I’ve done to try to locate/fix the problem
A) New spark plugs
B) Cleaned distributor cap / rotor
C) Tested all spark plug cables (removed all cables one by one while the engine was running and verified a change in engine noise)
D) Air filter inspected
E) Vacuum hoses inspected, tested for leaks using break cleaner
F) All connections to the gas tank inspected
G) Tested for fault codes – no faults found
H) New lambda sensor (O2 sensor), fuse for O2 sensor heater tested with multi-meter
I) New cold start sensor (coolant temperature sensor)
J) Added 600ml of Bardahl fuel injector cleaner to 1/2 a tank a gas and ran it until gas tank almost empty
(recommended by the guy in the autopart-store)
K) New Intake Air Temperature (IAT) sensor
L) MAP sensor tested with vacuum pump
M) Throttle position sensor tested with multi-meter
N) Injector tested with multi-meter (1,3 ohm measured)
O) Idle speed control actuator (ISC) tested
– app. 3VAC between pin 1 & 2 in idle
– pressure applied to springloaded rod = pin 3 & 4 shortcircuited
– no pressure on springloaded pin = pin 3 & 4 disconnected
P) Charcoal Canister Purge Valve tested to 30ohm
Q) Fuel system diagnosis performed – injector clicks, 13hz – idle valve clicks, 1hz – EVAP valve clicks, 2hz
R) New fuel filter

The car uses no fluids, besides gasoline.
The problem is very consistent – the car behaves the same every day.

Any help is greatly appreciated.

Thanks
Soren Nielsen

Topic

[Rudy Wilmoth]

🙂 Did you have this drivability problem before the gas tank was removed ? If you did not, I would return to the place that removed the gas tank and have them check their work. Something was altered when they did their work if the problem was not there before the repair. If you had the drivability problem before the gas tank was removed, then I am wrong and more research will be needed to be done by me about this.

[Soren Nielsen]

I removed the gas tank myself.
The problems 1-4 started happening right after this.

[Kylie]

maybe a faulty fuel pressure regulator?

[Soren Nielsen]

Thanks for your input.
I’ll take the fuel pressure regulator apart this weekend and clean it.
I’ll let you know how it turns out.

[Kylie]

Does your oil smell like petrol? Usually this is a pretty good sign that the FPR is playing up. Or pulling the vacuum line off of the FPR and seeing if that smells of petrol or if the car is running the petrol may bubble out of the vacuum plug if there is a hole in the FPR diaphragm.

[Soren Nielsen]

Thanks again.
I’ll look into the things you mention this weekend.

[EricTheCarGuy]

Yea, if the problem started after you removed the tank, that’s where you’ll likely find the issue. I was thinking something with the canister purge while reading your post, but I suppose it could also have something to do with the fuel pump or psi regulator as suggested. Also check for any pinched wires, vacuum lines, or connector issues that might have happened when the tank was reinstalled.

Keep us posted on your findings.

[Soren Nielsen]

I have tested the canister purge (EVAP) valve (see P and Q in my first post)
The fuel system diagnosis was performed by means of the small diagnostic box mounted behind the left-side strut tower in the engine compartment. I could hear the EVAP valve clicking so I suspect it’s ok.

I can’t find any pinched wires, hoses or connectors. I even lowered the tank a second time to do a visual inspection, but everything looked ok.

I’ll see if I can get a hold of a fuel pressure gauge to test the fuel pump pressure.

Thanks for your input.

[EricTheCarGuy]

Just because a valve ‘clicks’ that does not mean it’s OK. I’ve seen this in the past with evap valves. The only way to really check them is with smoke. I’ve had valves click that actually leaked. EVAP diagnosis can be a pain I know, but it’s often almost impossible without a smoke machine of some kind. Also, the canister purge is not the only valve in the system. That said, checking the fuel pressure is a great idea.

Keep us posted on your findings.

[Soren Nielsen]

I just finished disassembling, cleaning and reassembling the fuel pressure regulator.
Everything looked fine as far as I could tell. See attached photos.

I didn’t have the nerve to remove the membrane in fear of tearing it to pieces.

My oil does smell like petrol.
I don’t see any way of removing the vacuum connection to the FPR.

The fuel pressure test is still pending as I need to find some hose fittings suited for the job.
I already have the gauge and a Tee-fitting.

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[Kylie]

Yes, well, it will be interesting to see the results of the pressure test.

Could be leaking injector/s? Again, just because it is clicking doesn’t mean that it is not faulty.
Does it seem like the car is flooded when you’re trying to start it?
Does the uneven idle smooth out if you feather the accelerator?
Does the exhaust smell petrolly?
Have you had a rise in petrol consumption?
Also, do an engine compression test, just to be sure.

[Kylie]

The info on these sites may help also:

http://www.fuelpumpu.com/news-all-you-need-is-a-fuel-pressure-gauge-to-get-you-started.aspx

http://www.autotap.com/techlibrary/diagnosing_misfires.asp

I was just thinking that it might pay to check the coolant temp sensor also.

[Soren Nielsen]

Does it seem like the car is flooded when you’re trying to start it?
Now that you mention it. Yes, it takes a few seconds before it fires when it has been standing for a while.

Does the uneven idle smooth out if you feather the accelerator?
Yes, if by feather you mean push the accelerator slightly.

Does the exhaust smell petrolly?
Yes, see 3) in my initial post

Have you had a rise in petrol consumption?
Yes, see 4) in my initial post

Also, do an engine compression test, just to be sure.
I’ll see if I can get a hold of the required tools.

I already replaced the coolant temp sensor. See I) in my initial post.

One more thing that I’ve noticed.
If I disconnect the coolant temp sensor, the green lambda triangle in the dashboard turns on – the car enters limb mode.
This pretty much eradicates problem 2) “Hesitation on acceleration” and makes the car much better to drive.

I’ll be sure to study your two links.

Thank you for your patience and perseverance. Much obliged.

[Kylie]

No worries, Soren.

Cars are such a headache lol.

It might pay to have another look at your MAP or MAF sensor?

The sensor itself can cut in and out during operation. So checking it with an ohmmeter with engine off and key in the “on” position may not necessarily uncover a malfunction. You can try to back probe the connection, try unplugging it and starting the car and see how it behaves afterward OR if you can afford to maybe replace the part.

The car should go into limp mode if you unplug something.
http://www.grego.ca/limp.htm
Though the fact that it improves the performance of the car is curious…and might be worth investigating further.

[Soren Nielsen]

I’ll have another look at the MAP sensor this weekend.
The readings from the MAP sensor were as follows last time:
0 = 4,8V
-100mBar = 4,28V
-200mBar = 3,77V
-300mBar = 3,26V
-400mBar = 2,7V
-500mBar = 2,2V
-600mBar = 1,7V
-700mBar = 1,17V

This time I think I’ll run a wire from the MAP sensor to the dashboard and monitor the signal with my multimeter while I drive.

What do you make of the oil smelling like petrol?
Do you think it’s simply due to the car running rich?

By the way, this morning and this afternoon the car started right up (not flooded).
I’ll keep an eye on this from now on.
The hesitation and jerking on acceleration with cold engine was still present though.

[Author]

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