sudden loss of power (92 ka24de)

[aradapilot]

I drive a 1992 240 with a ka24de bone stock, save for high-flow injectors. 120k on the block and 20k on the head. she ran absolutely flawlessly until monday, when on the way home from work (~80mph on highway) I noticed a significant loss of power and more irregular engine noise, chugging, like a misfire. When I got down to normal road speeds there was significant shaking, and my idle bounces between 500-1000 where before it held a perfect 750. Stalled once at idle. The motor shakes like a bastard at idle. Also there is now a distinct rattle coming from the motor, especially from 1000-2000 rpm

Also, when holding a steady throttle under no load...i.e. in neutral revving to 3500, it will not stay there...drops to 3000 or even 2500 with no change in throttle, then comes back up to 3500.

ECU throws no codes. plugs, wires, injectors, fuel filter I've changed recently. O2 sensor went a while back and was an easy fix, but it shouldn't have gone already. ECU test on the O2 sensor gives only 2-3 blinks per 10 secs as opposed to the 5 that are expected.

One thing I noted is that this started about 30 miles into a new tank of gas from a no-name station I stopped at when almost empty the night before. Am I just running on bad gas? I threw 2 cans of drygas into the tank, but I've only burned about a quarter of it so far as I haven't driven much since this started...but I've never had contaminated gas before and don't know the signs aside from what I've seen posted here which looks similar. If so, what sort of damage am I looking at? will that o2 sensor need replacing? new tune up? or is there another thing that might be wrong? Just surprised that this came about all of a sudden after thousands of miles of perfect running.

here is a (bad quality) recording of the rattle noise: http://www.zeropride.com/0618081823.wav

thanks for your input...

[Bboy/dorikun88]

The rattling sounds like it could be a loose timing chain as for the sudden iraddic shaking of the engine and unsteady idle ive never heard of fuel doing that to an engine unless worse case scenerio is the a/f mixture in your combustion chamber predetonated and put a hole in the top of your piston wich might explain the rattling from the engine. Id say get a compression test done on your engine to eliminate that possibility then check for any possible vaccum leaks and go from there. Good luck bro hopefully its not as bad as i think it might be.

[aradapilot]

oof. that would not be good. but if the piston's destroyed why would it vary so much? here's to hoping that isn't the case.

I've got a compression gauge somewhere, i just need to dig it out. I'll have to do that test tomorrow...big storm came tonight and I don't have a garage to work in (rain into cylinders is not a good idea).

would any damage like that have been noticable? like a loud bang or whatnot? seems like blowing a steel plate wouldn't be peaceful...and this problem just developed over the course of 20 miles or so.

haven't removed a head in a long time. would rather not have to, i'm probably rusty on the details.

[1slowS13]

maybe it is bad gas. i had a buddy of mine fill up a whole tank from a no name station, drove home fine. the next morning, he went to work and his car started acting up. it ended up just being bad gas and a dirty strainer on his fuel pump.

[aradapilot]

that's what I'm hoping. I need to find a way to get rid of 12 gallons of gas then, fill it with 93 to dilute the rest of it, swap fuel filter...maybe run some injector cleaner through to be safe. I just don't know how to get rid of so much gas without running it through the car, and that seems like a poor idea at this point. I'd rather not risk preignition damage any more than i have to.
and pouring it into the driveway in a crowded jersey suburb seems like trouble...

[aradapilot]

so i drained the tank (hotwired fuel pump, hooray) and put in 10 gals of premium. should offset what was left in there. swapped in a new fuel filter and new plugs, the old plugs were (suddenly) dirty as hell but they fired when i tested them. also compression gauge showed ~175psi in all cyls. didn't have time to put any miles on it last night after this, but this morning i took her to work (30mi?)...marked improvement, but still not perfect. seems like that 4th cyl kicks in at higher rpms, then will stay going for a while when i drop them, then after a bit it goes back to how it was, then back to good, etc.the rattly noise is worrying me...though i'm thinking it could be the timing chain guides? wasn't that a common issue in ka24de's? is this possible and if so is it a case of 'fix this or the chain breaks' or is it just an annoyance?
so what could be left wrong with this...maybe a bad O2 sensor? could that cause an issue like this? it looks like an easy replacement, right out in the open.

[los_inc]

check your injectors they might be clogged to shit
-los