1995 850 Intermittent misfire at idle / accel.

jnitschke123 · Post by **jnitschke123** » 12 Dec 2015, 09:25

The ignition coil looks like an original part. What tests can be performed to check out the performance of it?

Post by **erikv11** » 12 Dec 2015, 11:06

IMHO coil failure is super rare, but testing things is usually a good idea.

What the heck is that MAF? I have only ever seen 4-pin connectors on an 850, looks like that is only 2 pins, and I have not seen the MAF housing molded into the air box like in your 9161031 box. Is there a part number on the blue plug? I am confused about that; it is the right location for a MAF though. OK, this must be a 10 valve car; e.g. https://www.matthewsvolvosite.com/forums ... =1&t=62034. So that wuld be a Siemens MAF, you don't want a Bosch disregard that.

The recent tune up by a used car dealer could raise a red flag, although if they know Volvos then maybe they know what to buy. But, the wires must be Bougicord, the cap and rotor must be Bosch, there are more options on the plugs but it is easy to screw up there too. I would definitely look under the cap make sure there is no moisture or oil from a blown cam seal.

For the MAF test, you have to test the car under conditions where it might stutter. I.e. unplug it and drive around. Best to not unplug and/or replug it while running, do it with the car off. Very strange that it didn't turn on the CEL, are you sure that bulb is functional (check when all the lights turn on when you turn the key)?

You seem to have ruled out the CPS wiring, good to cross off the list!

jnitschke123 · Post by **jnitschke123** » 12 Dec 2015, 12:04

Yeah, I'm positive that it is a 10 valve car since it doesn't have '20-valve' lettered on the plastic spark plug cover.

I check the plug wires and they are bougicord. The cap is a bosch part. The plugs are Volvo OEM plugs and they look brand new.

Is the CEL the light with the green triangle and the weird symbol? If so, it does not light up when I cycle the key. The car is OBD 1, would this be why the light doesn't go on? Maybe OBD 1 850s didn't have the weird symbol light as part of the diagnostic system yet.. idk

Post by **abscate** » 12 Dec 2015, 18:35

No CEL on OBD 1 I'm guessing.

A coil tester looks just like your old coil, except it's new.you bolt it in exactly where your old coil is now.

( seriously it's tough to diagnose a miss in a coil without RR). Maybe someone here in Canada has a spare you can swap out to test ??

jnitschke123 · Post by **jnitschke123** » 12 Dec 2015, 23:47

The ignition coil could be a possible culprit. The dealer where I bought it from probably (hopefully) has some spare ignition parts for a 10-valve. I have an appointment to bring it in on Thursday. Fingers crossed that it acts up for them!

I've narrowed it down to these parts that may have gone wrong, listed in order of what I think it is to what I think is less likely:
-Cam Position Sensor failure
-Mass Air Flow failure
-Ignition Coil breakdown
-Fuel pump relay failure
-Throttle Position switch failure
-Dirty fuel injectors

I'm also going to check the OBD 1 diagnostic unit that is located under the hood to see if there are any codes stored there. I'll give this a shot tomorrow and update the post as necessary.

As an aside, I am getting about 450 km per tank in mostly city driving using Mid-grade (89) octane fuel. Is this right about average?

Cheers!

Post by **erikv11** » 13 Dec 2015, 01:59

Yes, retrieving codes is step 1!

99 out of 100 times when the CPS goes, the car will not run. It gives a no-spark condition. Otherwise those are all reasonable items on your list.

It is free to pull the distributor cap and check inside it for moisture and/or oil, as would be present with a blown rear cam seal. Very common, especially if the PCV service history is not so steady. A blown rear cam seal will usually give multiple misfire codes, but not always. Worth a look since otherwise the ignition parts checked out A-OK.

Fuel economy sounds about average, yes.

jnitschke123 · Post by **jnitschke123** » 13 Dec 2015, 14:42

Okay, I just pulled some codes from the OBD 1 diagnostic port under the hood. It returned these fault codes:
- 121 - MAF sensor signal
- 521 - Front HO2S Preheating
- 243 - Throttle Position sensor (TPS) signal

Here's the bit that confuses me: Since my car doesn't actually have a MAF sensor (10-valve engine, siemens engine management) and uses a combination of a MAP sensor (near the radiator) and an air temp sensor (where the MAF sensor would usually be) to measure engine air flow, should I suspect that these parts have failed or have a bad connection?

Post by **misha** » 13 Dec 2015, 14:55

It's not a Maf....it's Air Temperature Sensor(air thermistor).
10 valve cars have totally different sensors because they have different engine managements than 20v cars.
This car doesn't have Maf...it have MAP sensor instead of Maf.

Check Map sensor's connector and it's vacuum line.
http://www.volvoforums.org.uk/showthread.php?t=39003

jnitschke123 · Post by **jnitschke123** » 13 Dec 2015, 15:43

I know that, thats why I said, "Since my car doesn't actually have a MAF sensor (10-valve engine, siemens engine management) and uses a combination of a MAP sensor (near the radiator) and an air temp sensor (where the MAF sensor would usually be) to measure engine air flow..."

Post by **misha** » 13 Dec 2015, 15:58

It's not measuring air flow,it measures temperature of air which is coming into engine.That's why it's called air temperature sensor.

My previous post wasn't reply to your post.....it was for erikv11 post,but while i was posting both of you allready replied.

1995 850 Intermittent misfire at idle / accel.

Re: 1995 850 Intermittent misfire at idle / accel.