94 850T check engine light while accelerating

[henrysin44]

...That would definitely explain why my headlights would be dim until i started driving.

You had a good luck that your battery was in good shape.
Since you ran a car with low voltage charging system...i would suggest to remove negative battery terminal for a few hours in order to reset car's management system and all bad things it could catch because of low voltage.

After that,perform a re-learning procedure for ecu and check voltage output on battery terminals.
Re-learning procedure:
http://www.volvotips.com/index.php/850- ... rocedures/

I'll give that a try, your probably right especially sense the CEL was on only during load.

[henrysin44]

...That would definitely explain why my headlights would be dim until i started driving.

You had a good luck that your battery was in good shape.
Since you ran a car with low voltage charging system...i would suggest to remove negative battery terminal for a few hours in order to reset car's management system and all bad things it could catch because of low voltage.

After that,perform a re-learning procedure for ecu and check voltage output on battery terminals.
Re-learning procedure:
http://www.volvotips.com/index.php/850- ... rocedures/

Gave it a try but unfortunately im still getting a CEL under load only....this is weird....car starts faster now though

[erikv11]

Number one hypothesis here is knock under load. I'm not sure how to track that down but some ideas are to make sure the engine is not running lean, that the knock sensors are connected and mounted, that you are using proper octane fuel.

[henrysin44]

Number one hypothesis here is knock under load. I'm not sure how to track that down but some ideas are to make sure the engine is not running lean, that the knock sensors are connected and mounted, that you are using proper octane fuel.

Just got back from a 10 day road trip and the CEL is still doing its thing. Ill check for vacuum leaks and start filling up with premium (been using regular ever sense the pandemic started). I put new copper spark plugs (runs a little smoother) and double checked the big 3. Really hoping to solve this one

[scot850]

Never run a turbo on regular particularly under load or on the highway. Quickest way to get burnt valves.

Have you tried swapping in used knock sensor? How worn is the distributor shaft? I'll have to go back through this long thread to see what parts you have swapped out.

Neil.

[henrysin44]

Never run a turbo on regular particularly under load or on the highway. Quickest way to get burnt valves.

Have you tried swapping in used knock sensor? How worn is the distributor shaft? I'll have to go back through this long thread to see what parts you have swapped out.

Neil.

Good to know! I knew it wasn't a great thing to do but I don't want to get burnt valves. I haven't swapped the knock sensors, but wouldn't faulty knock sensors store a code? What do you mean by distributor shaft, cam shaft? I replaced the distributor cap and rotor last summer and everything looked good.

As an update I gaped my new plugs at 0.26 (from 0.28) and filled my empty tank with premium, now the check engine light only comes on during WOT and almost WOT, or if not in the appropriate gear.

[scot850]

Have you changed either the cam or crank sensors in the recent past?

If your distributor shaft (the shaft with the rotor arm on it) is worn it can accelerate the wear on the rotor arm causing spark drop off or damage to the distributor cap.

Have you checked inside the distributor cap recently to make sure there is no moisture or oil from a leaking cam seal in there?

Neil.

[erikv11]

The knock sensors rarely, rarely, rarely go bad. However the wire to them can be come frayed, so it is definitely worth checking the connections. Since they never go bad I have no experience with or reading about knock sensor codes but yeah, I too would expect a bad one to set a code.

Neil's point about ignition parts is a good one, especially since plugs may have made a difference. What is the vintage on the plug/coil wires? They have a date code stamped on them.

[henrysin44]

The knock sensors rarely, rarely, rarely go bad. However the wire to them can be come frayed, so it is definitely worth checking the connections. Since they never go bad I have no experience with or reading about knock sensor codes but yeah, I too would expect a bad one to set a code.

Neil's point about ignition parts is a good one, especially since plugs may have made a difference. What is the vintage on the plug/coil wires? They have a date code stamped on them.

Ill take a look, the OEM plug wires came from a pre coil pack V70 T5 at a scrap yard, they look quite good in and out but that could be the weak link as every other ignition component, besides the coil, is new.

Today i finally got around to installing an exhaust, it was just a down-pipe prior, and with the car now quiet i was able to notice the light comes on when it hits max boost, and when that light comes on the boost pulls back a few PSIs, something i didn't notice when the car was insanely loud.

[henrysin44]

Have you changed either the cam or crank sensors in the recent past?

If your distributor shaft (the shaft with the rotor arm on it) is worn it can accelerate the wear on the rotor arm causing spark drop off or damage to the distributor cap.

Have you checked inside the distributor cap recently to make sure there is no moisture or oil from a leaking cam seal in there?

Neil.

Well the engine has about 366K on it so i wouldn't be surprised to find oil in the distributor cap, ill give it a look.