Mechanics

HARD TO START; HESITATES; AFTER WARM-UP, RUN

1998 Volvo V90

Engine Performance problem
1998 Volvo V90 6 cyl Two Wheel Drive Automatic 208000 miles

For some time, the car is ahrd to start. If I push on the accelerator normally, the engine acts like it wants to stall. If I push on it very slowly, it will acclerate. After about 20 minutes, the engine starts to run rough. If I turn the car off at this point, it will not crank until it has cooled off completely, several hours. I have a code reader which shows live data. It says that the rear heated O2 is faulty. I replaced it and the scanner says that it is still faulty (bad ECM?). The scanner shows the timing is 9 degrees advanced. It is a distributorless ignition, the ECM controls the timing. After the warm-up, the timing starts to jump sometimes to 12 then back to 8 or 9, then maybe to 15 and back to 8 or 9.
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Graychap
April 4, 2010.



Hi
How recent is tune up? Any recent repairs? How many miles on Timing belt? Has fuel pressure been checked? Needs to be 42.6 psi
Let me know
Thanks for donate

Docfixit
Apr 5, 2010.
Don't know last tune-up. Bought car at 208000. Car was running fine. Wife hardly drives it, spent a lot of time idling in driveway, battery died once or twice between cranking. I just bought fuel pressure tester, haven't used it yet. Changed fuel filter, little bit of stuff came out of it. Don't know timing belt, previous owner appears to have had car serviced at Volvo dealer regularly (all Volvo OEM stuff, even spark plugs).

Tiny
Graychap
Apr 5, 2010.
What I suspect is that you could have a faulty mass air flow sensor and would recommend that you actually take it in to a shop for proper diagnosis. Here is a description of the mass air flow sensor operation.

The mass air flow (MAF) sensor transmits a signal to the engine control module (ECM) about the intake air mass.

This information is used to calculate: injection period
ignition timing
if the engine cooling fan (FC) needs to run-on.
The mass air flow sensor consists of a plastic housing containing a connector, electronic circuitry and an aluminum heat sink. The mass airflow sensor measuring device is a heated film mounted in a pipe which is cooled by the intake air to the engine. The heated film consists of four resistors: The mass air flow sensor is supplied with battery voltage and has separate power and signal grounds. The signal from the sensor varies from 0 Volts to 5 Volts depending on the mass of air passing. Voltage increases with air mass.

Since working temperature is relatively high (170 °C (338 °F)), and the flow and temperature sensitive resistors are mounted on the side of the hot film, a burn-off function is not required.

The engine control module adopts substitute values if the mass air flow sensor signal is missing or faulty.

The mass air flow sensor is located between the air cleaner (ACL) cover and the fresh air intake.
.

Most of the time the mass air fow sensor will not post a trouble code but can give you the symptoms you are experiencing like your hard start, hesitation and even at times stalling out when slowing down or coming to a stop. This sensors can be pretty expensive, maybe $300-$400 from the dealer and would strongly recommend buying one from there. That is why you should take it in for proper diagnosis. Also can you post the oxygen sensor code you got? If the mss air flow sensor is faulty this could be related or it may not? But you also need to reset the adaptations in the engine control module. You can do this by removing the engine control module out for a couple of minutes. That way you reset your fuel trims back to 1.0

JIS001
Apr 6, 2010.
I put a test guage on the schrader connection at the fuel rail, started the engine and got 10psi. Is that enough? Chiltons says it should be 43.5psi.

Tiny
Graychap
Apr 18, 2010.
No, that is too low. In the rear right next to the fuel filter is another test port. Install gage to see what you rear back there also. If you get the same thing make sure you have plenty of fuel. If you have fuel in the tank with the same readings then your pump is failing.

JIS001
Apr 19, 2010.
Same pressure at other test connection. Now, I've got to figure which fuel pump is correct. I see a wide range of prices, from $65 to $365. I see one at autopartswarehouse. Com for $95 that says direct OE replacement.

Tiny
Graychap
Apr 20, 2010.
I bought and installed a new fuel pump. I now have 36psi at the fuel rail. The car starts fine, runs fine. We drove it around for over an hour a couple of days ago, no problems. Lesson learned- 'misfire' code? Check fuel pressure.

Tiny
Graychap
May 26, 2010.