97 NA850 troubleshooting, no codes, out of ideas

waynej · Post by **waynej** » 31 Oct 2011, 10:04

Tried to monitor injector pulse width but the "pulse width/%duty cycle" function on my meter is no longer working. I used a millivolt scale to get comparable readings at different throttle positions. Was raining so couldn't drive with meter on windshield- just revved engine in garage. Reading 39 at idle, engine would go to 3500 RPM and no higher with a reading of 300, this was with about 50% throttle. Slowly increased throttle to 100% and injector reading stayed at 300 and sound of engine changed greatly even though RPM was still at 3500. Sounded very weak! The ECU must be limiting the max fuel flow for some reason.

Changed cam position sensor(I have a parts car not a big bank account) and took it for a test drive. No improvement, will go to 2500 RPM in 2nd with light throttle. With full throttle will only go to 2000 with very strong surging, almost like the key was being turned off and on very quickly. Will try to get time to change crank sensor this evening.

Post by **jblackburn** » 31 Oct 2011, 10:15

Have you ruled out any possibility of a big air leak or related sensor?

Intake manifold freeze plug loose perhaps (behind power steering pump)? Bad/crimped gasket on the intake manifold?

waynej · Post by **waynej** » 31 Oct 2011, 11:58

Yes I have checked for vacuum leaks and fixed 2 and it sounds like Andy has done extensive vacuum leak checking. It seems to me that a vacuum leak would cause a rough idle and we both have very smooth idles. A big enough vacuum leak to cause this serious a problem would mean it couldn't idle and maybe couldn't even start. I thought the most likely sensors were MAF and O2 but Andy has replaced those with no results. I see the online parts sellers are showing an altitude sensor. I don't know where it's located, can anyone point me in the right direction?

Someone in this thread said it had to do with under hood temp not engine temp. That sounds at least partly correct as the problem is worse on hot days. There must be something besides under hood temp. In the early stages it takes an hour or 2 to show up and it should only take 20 or 30 minutes to raise under hood temp. In the latter stages (just before death) it takes 1 or 2 minutes on a cold engine ( 40 to 50 degrees where I live) and on an engine that been off 5 minutes it takes about 15 to 30 seconds. This would be about the time it takes to go into closed loop which would indicate an O2 sensor, but that wasn't it.

waynej · Post by **waynej** » 31 Oct 2011, 13:30

Does anyone know where the grounding point for the ECU is? On the Djetronic (71-73) there are similar problems when the grounding points get corroded. I have searched for grounding points on the 96 850 and fine none. I checked my parts car (93 850) which is partly stripped and easier to see things. I see some in front of the battery but nothing near the ECU and on the 96 the points by the battery are not being used.

Checked the voltage at the injector plugs while disconnected from the injectors. On + side 14 volts at all 5. ON - side 7 volts on #'s1 to 4 and 4 volts on # 5. Does anyone know if Volvo is firing more than one injector at a time? If they are being fired separately I should not get that much voltage at ground. If they are firing more than one at a time it would be possible to get that much depending on what type of solid state switching device they use to pulse the ground. Maybe someone out there would have time to see what voltage you have at the injector plugs ground side. The engine idles fine while unplugging one injector at a time.

Post by **misha** » 31 Oct 2011, 13:46

waynej wrote:...The engine idles fine while unplugging one injector at a time.

I think that it should change idle speed while you doing that.It should act the same or similiar as you disconnect spark plug wire....engine should develop misfiring.

I can't figure out why it acts the same while you disconnect injector plug,it should misfire.

waynej · Post by **waynej** » 31 Oct 2011, 13:54

It does lower the RPM for a second but the ECU opens the IAC so it idles smooth while the voltages are checked with no danger of stalling.

waynej · Post by **waynej** » 01 Nov 2011, 17:31

Replaced crank sensor-no improvement.

waynej · Post by **waynej** » 06 Nov 2011, 22:09

[quote="div4scpro"]next bit of data:
no rattling sounds or any loose pieces falling out, don't know if a converter can be failed in the middle without
evidence at either end. can a converter's condition be definitively determined removed from the vehicle? [/quote]

The newer cats are the dual catalyst type. In the rear section the catalyst is on a ceramic matrix which sometimes disintegrates after thousands of heating and cooling cycles. In the front section the catalyst is on a metal matrix which never seems to break down. Since the ceramic portion almost always goes first at the front it is very likely that it would look good from both ends even if it was bad inside.
Whacking mine hard while on the car produced no rattling. When I got it off very hard shaking produced a very small rattle. A bad cat can come and go to some extent. When most of the disintegrated material is laying on the bottom the problem isn't as noticeable. When much of the material get pushed up against or into the honeycomb that's downstream from the bad area you have a serious flow restriction.