S70 rough running then stall [Sensor electrical plug corrosion] Topic is solved

patcal · Post by **patcal** » 23 Nov 2021, 11:02

I was driving home Friday night in my 98 S70 GLT. It was driving fine in stop & go traffic. All of a sudden the idle gets very erratic. I thought it was going to stall but it never did. When I put it in neutral, it did the same thing. Real rough running. When I gave it gas to around 2500 rpm it settled a little. All the while creeping about 1-15 mph. After about a mile of this, it returned to normal & ran fine all the way home. There were not any codes when I ran for them on Saturday morning. It started & ran fine as it always does. Any thought on this? I am saving to do control arms & inner tie rods for my S60. So today finally died on me. Started to do the same thing, then stalled & she's done. Threw codes for multiple misfires on all cylinders. There seems to be fuel in the rail but I have no idea if it's enough. I have a fuel pressure gauge coming tomorrow. I tried jumping the relay with no success. Any thoughts?

Post by **erikv11** » 23 Nov 2021, 12:42

Could be fuel, compression, spark or timing.

Fuel you've started to look at. I'd definitely look carefully at the fuel pump relay and the fuel pump, however. That's still a top suspect at this point.

Timing problem seems unlikely. Same with compression.

Looking at spark: I'd pull the distributor cap and inspect carefully. How is the rotor? Is there any condensation or oil in there? While you're at it how ore the plugs, but a dist/rotor problem would make more sense with the symptoms.

Other less likely possibilities regarding spark: check the plugs for spark; could be a sensor crapped out (crank sensor or cam sensor, even throttle position sensor for that matter).

patcal · Post by **patcal** » 23 Nov 2021, 13:05

erikv11 wrote: ↑23 Nov 2021, 12:42 Could be fuel, compression, spark or timing.

Fuel you've started to look at. I'd definitely look carefully at the fuel pump relay and the fuel pump, however. That's still a top suspect at this point.

Timing problem seems unlikely. Same with compression.

Looking at spark: I'd pull the distributor cap and inspect carefully. How is the rotor? Is there any condensation or oil in there? While you're at it how ore the plugs, but a dist/rotor problem would make more sense with the symptoms.

Other less likely possibilities regarding spark: check the plugs for spark; could be a sensor crapped out (crank sensor or cam sensor, even throttle position sensor for that matter).

Thanks for the response. Is there a way to actually test the fuel relay? If I have spark at the plugs, can I rule out the cam & crank sensor?

Post by **erikv11** » 23 Nov 2021, 13:40

Yep, bad cam sensor or bad crank sensor will give a no-spark condition.

Test the fuel relay by removing it and "jumpering" the socket with a wire or paper clip. E.g. https://www.matthewsvolvosite.com/forum ... hp?t=18663 but you can find many posts here if you want to read more about that method. Basically put in a bypass and if that fixes the problem then you need a fuel pump relay.

patcal · Post by **patcal** » 23 Nov 2021, 14:20

Well I have spark out of the coil. I pulled a plug & tried to see but it's too bright out & I was alone. Jumping the fuel relay made no difference. Like I said, I do have fuel in the rail but not sure if it's correct.

Post by **abscate** » 23 Nov 2021, 19:03

Pull off the distributor cap and let’s see pictures of the cap and rotor. Spark at coil won’t be useful if it doesn’t make it to the spark plug

Example of shot parts….

patcal · Post by **patcal** » 23 Nov 2021, 19:17

Thanks. Will check that in the morning.

Post by **abscate** » 24 Nov 2021, 05:06

You will need a longish 3mm hex key to get those rotor bolts off, bit of an oddball size

patcal · Post by **patcal** » 24 Nov 2021, 10:28

Well, I didn't get very far. The fuel pressure gauge has all these fitting but not one that fits the shrader valve on my car. On top of that, I broke one of the nipples on the vacuum tree just by lightly bumping it. My son is going to come over later to help me check for spark while cranking.

Update: Got fuel pressure gauge to work. 45PSI which I think 43 is specified. Also, I have spark at the plugs. Good white spark. Also notices fuel in the spark plug holes so I know the injectors are working. Unhooked the MAF sensor & still no start. Not sure where to look now. Timing maybe?

patcal · Post by **patcal** » 26 Nov 2021, 09:55

Well, kind of a final update. The timing belt is fine. Actually looks real good. The compression however is bad
#1 - 145
#2 - 195
#3 - 125
#4 - 105
#5 - 65.
I didn't do a wet test cause I am so bummed. The question is even with that compression, wouldn't the car try to start? I think she's done for.