1997 S90/960 B6304S, Misfire on 4&5 only. Topic is solved

[RickHaleParker]

Random misfire on 4 and 5 only, below 2000 RPM. DCT P0300, P0304, P0305.

Misfires only on 4 and 5 and only below 2000 RPM. Wrap up to 2000+ RPM and clear the codes, codes will not come back untill the RPM drops below 2000. You can also hear the misfires quit above 2000 RPM.


1. Compression test 180 PSI +-3 PSI on all six.

2. Sprayed either around intake manifold, no effect.

3. Swamped coil packs and plugs set 2 and 3 with set 4 and 5, no effect, misfire does not follow coil packs and plugs.

4. Checked electrical connections on coil packs 4 and 5. The rubber is deteriorated but I got the connectors on the pins of the coil packs. No effect.

5. Not a weak battery, just replaced battery and voltage is correct.

I thought about switching the Motronic power stage modules one and two (AKA ignition modules) to see if the misfires would jump from 4,5 to 2,3. Tight fit on the back side, would like to gather other ideas and options before I try that.

Anybody got some experience with these symptoms? Other theories?

Rick H Parker

[RickHaleParker]

Swamped positions of Motronic power stage modules one and two (AKA ignition modules), no effect.
Swamped position of fuel injectors 2,3 with 4,5, no effect.

[93Regina]

Other theories?

VOLVO ALL MODELS


ECM Programming
When replacing Transmission Module (TM) or Engine Control
Module (ECM), use Volvo System Tester to clear DTCs and reset adaptive
functions. Follow manufacturer's instructions and tester prompts.

After disconnecting battery or replacing ECM, drive vehicle
to enable ECM to relearn driveability. Inform your customer that they
may experience driveability different from what they are accustomed to
until ECM completes relearn function.
===============================================

I know nothing, but clear DTCs, and disconnect battery for a hour

[RickHaleParker]

Good luck in locating a Volvo System Tester.

Engine and transmission DCTs where cleared using Vol-FCR before posting this. Have done over 200 miles at highways speeds since.

[93Regina]

200 miles at highways speeds since.

I know nothing, but clean up the relevant grounds.

What is needed is a scope or automotive DVOM, to examine ground pulses (I assume) to each coil. I assume each coil is fed 12 volts, and ECM grounds coil.

[RickHaleParker]

The coil packs are on a common 12v buss. The grounds are pulsed by the ECM through the Motronic power stage modules.

I think I need to go back and do a full compression test, Static, Dynamic and Snap.

[[email protected]]

Could be lots of things. Possibly a vacuum leak causing lean running on 4 and 5? Bad intake manifold or manifold gasket? That is but one of many possibilities.

[RickHaleParker]

Intake gaskets are new. I Sprayed Either around the intake manifold looking for a leak, if there was a leak it would suck in the Either and the engine would surge.

Been busy, I might get around to doing a full compression test soon.

[jimmy57]

Do the ether test around the "tree" where all the vac lines attach aft of throttle. The conditions you describe sure seem to be air leak caused as the amount of leak becomes a smaller percentage as you speed up the engine and consumption goes up. Manifold vac goes down and the flow into leak spot also goes down effectively making a leak go away with larger throttle opening. When monitoring for air leaks on intake the fuel trims for idle will go to full enrichment while off idle may show almost nothing out of line.

[RickHaleParker]

Did the compression test today, Still working on an interpretation.

Barometric pressure 30.12 in, Tempture 71F.

Compression tests.

CYL: -----------(1)-------------(2)------------(3)-------------(4)------------(5)-----------(6)
Static:-------230 PSI--------215 PSI-------220 PSI-------210 PSI-------215 PSI------190 PSI.
Dymanic:--125 PSI 54%--120 PSI 56%---125 PSI 54%--100 PSI 56%---90 PSI 42%---90 PSI 47%.
Snap:------160 PSI 70%--150 PSI 70%---60 PSI 72%----140 PSI 66%--130 PSI 60%--120 PSI 63%.