98 S70 GLT Misfiring Under Load Topic is solved

ferocity02 · Post by **ferocity02** » 09 Dec 2019, 11:57

For the past year or so my 1998 S70 GLT has be misfiring under heavy load, typically at high speed (60+ mph) when going up a hill. The issue is worsened when there are a lot of people and/or luggage in the car. The misfire causes a flashing check engine light and a consistent vibration. Driving around town and idling the car sounds great and healthy. It will misfire with 87 or 91 octane.

We went on a ~400 mile road trip this weekend with I'm guessing 3-5 total minutes of misfiring resulting in the following codes:

EFI-451 Misfire emission level cylinder 1
EFI-453 Misfire emission level cylinder 3
EFI-454 Misfire emission level cylinder 4
EFI-455 Misfire emission level cylinder 5
EFI-543 Misfire emission level from at least one cylinder
EFI-545 Misfire with TWC damage from at least one cylinder
EFI-553 Misfire with catalytic converter damage cylinder 3

I have replaced the plugs with new copper plugs, wires with new Bougicords, the cap, rotor and coil with new Bosch units, the TPS sensor, knock sensors, and cleaned the MAF sensor and throttle body. These did not fix the issue.

Within the last 20k miles I've replaced the pre-cat O2 sensor, fuel filter, battery, air filter, PCV system, water temp sensor, and a variety of vacuum lines that were falling apart.

There's not much left to blame, but I'm thinking it could be:
Vacuum leak
Bad MAF sensor
Bad injector
Low compression/bad motor

jkaspar · Post by **jkaspar** » 10 Dec 2019, 08:31

MAFs are usually good for about 100k. If its original, I would replace it. On my P2 cars, I chased something similar at around 100k and in the end, I’ll just replace plugs, coils and MAF at 100k from now on (If I ever get one thats sub 100k, or take my SR to 200k).

Also, did you make sure the plugs were gapped properly?

ferocity02 · Post by **ferocity02** » 10 Dec 2019, 16:30

The MAF is original with 204k miles on it. Is there a test procedure? Are there any good aftermarket options, or do I need to go with OEM?

Plugs were gapped.

Post by **Clemens** » 11 Dec 2019, 16:40

2 things:

there is no alternative to the original MAF (should be Bosch, I think). others will throw codes.

the spark plugs on turbo cars need to be Volvo. others may be problematic even though some people get decent results with cheap plugs.

Klausc · Post by **Klausc** » 12 Dec 2019, 12:58

Spark plugs need to be copper core, just like the Volvo plugs, and gapped to .028

The only MAF test is to unplug it, then start the engine. You could try a MAF cleaner and see if that helps.

I would get a compression test, it will at least give you a baseline.

A really good code reader can tell you why there are misfires.

rasense · Post by **rasense** » 12 Dec 2019, 14:56

I was having similar trouble with my tuned 98 R at WOT. I didn't throw parts at it, but I decided to put new plugs in. I use NGK Coppers and checked the gap on the new ones and the old ones. Came gapped incorrectly out of the box---0.031 when they should be 0.028. I'd suggest taking a look at that. My car is running great again.

Post by **RickHaleParker** » 12 Dec 2019, 18:03

ferocity02 wrote: ↑09 Dec 2019, 11:57 EFI-451 Misfire emission level cylinder 1
EFI-453 Misfire emission level cylinder 3
EFI-454 Misfire emission level cylinder 4
EFI-455 Misfire emission level cylinder 5
EFI-543 Misfire emission level from at least one cylinder
EFI-545 Misfire with TWC damage from at least one cylinder
EFI-553 Misfire with catalytic converter damage cylinder 3

Under load only. I would start with the Charged Air pipe, leaks under pressure.

Possible source

defective spark plugs, ignition cables, distributor cap/rotor, ignition coil or flywheel/pulse wheel
blocked/leaking injector
uneven compression
leakage between cooling system and cylinder
moisture, flashover in ignition system HT side
intermittent open-circuit , intermittent short-circuit to ground, intermittent short-circuit to voltage supply, contact resistance or loose connection in ignition system low-tension side, in injector circuit or fuel pump (FP) circuit.
engine oil level too high
air leakage
fuel pressure and residual pressure.

Fault causes not included in the fault-tracing process, but which may still post a diagnostic trouble code (DTC):

fuel stoppage
water in spark plug wells
contaminated fuel or incorrect fuel
repeated cold starting where the engine coolant temperature (ECT) is not allowed to reach operating temperature between starts.

ferocity02 · Post by **ferocity02** » 18 Feb 2020, 15:11

Well, I think the issue was indeed the spark plugs. I installed Bosch 7955 FR7DC+ plugs and gapped them to 0.028". Went on a 500 mile road trip and the engine didn't skip a beat. There were numerous situations where the car would have normally misfired.

These plugs were gapped to 0.032" +/- 0.001" out of the box, so I had to shrink all of them.

The plugs that were in the car before were NGK BKR6E. I measured their gap at 0.033" +/- 0.001" (I must have not gapped them upon install). I guess that was enough to throw off the engine.

These turbo motors sure are picky about plugs!!!

Post by **RickHaleParker** » 18 Feb 2020, 15:52

ferocity02 wrote: ↑18 Feb 2020, 15:11
The plugs that were in the car before were NGK BKR6E. I measured their gap at 0.033" +/- 0.001" (I must have not gapped them upon install). I guess that was enough to throw off the engine.

These turbo motors sure are picky about plugs!!!

BKR6EQUP or BKR6EIX?
For both NKG specs the gap at 0.028 for a 1998 Volvo 2.4L".

Found this on the NKG website:
"While most NGK spark plugs are pre-gapped, there are instances where the gap requires modification."

Anybody care to advocate the pre-gapped myth?
A plug maybe pre-gapped but it does not mean the gap is correct for your application.

ferocity02 · Post by **ferocity02** » 18 Feb 2020, 19:53

Neither, I think they were NGK 6962.