Suddenly, car sounds like a lawnmower, loss of power

[Explodicide]

I was putting along going about 15 miles an hour (on the interstate in rush hour, so lots of 10-25 mph cruising) when all of a sudden I went to accelerate, and I noticed my engine was shuddering quite a bit. The exhaust also sounded much rougher, like a lawnmower, and I noticed a severe drop in power.

When leaving the car at idle it won't stall, but it it idling a little lower, sometimes hovering around 500 RPM. The RPMs don't fluctuate, they stay mostly consistent. After I parked it, I checked the exhaust a little more carefully, and it seemed to be blowing out some very fine blueish smoke. Maybe, it might just be because I had left it overnight and had just started it up.

I was afraid that I'd blown something in the head or the engine, so I tested compression, but all cylinders tested at a consistent 180 (*whew*). I just moved across the country, so I don't have all my tools / jacks, so I can't jack it up to check the exhaust, but some research indicates that it might be a hole somewhere in the exhaust.

The car is a 1990 body with an S13 DOHC motor swapped in, manual. It was running perfectly fine up until this happened on Friday. No CEL light codes before or after. All help is appreciated.

*EDIT* turned out it was a bad fuel injector in my #4 cylinder.
Modified by Explodicide at 6:05 PM 8/1/2009

[MisteenoMike]

SR or KA?

Since you already checked compression and it was fine (luckily) it's either an exhaust leak (less likely) or one cylinder isn't firing (more likely).

Does it shake more than normal? (Sitting in the car do you notice more vibration) If it does it's more likely that you're down a cylinder. (Exhaust leak creates more noise but not vibration)

We can offer more suggestions/solutions when you narrow it down...

[YuNg1's_240sx]

SR or KA?

The car is a 1990 body with an S13 DOHC motor swapped in, manual.

[kool-aid54]

I think your timing chain jumped a tooth. I don't recommend driving it too much. Mine did the same and I sold it and the guy didn't fix it and wound up throwing a rod. Anyway, I bet you cam is off a tooth. Just pull the cover and see if the gear lines up with the mark on the chain.

[MisteenoMike]

Uh, Yung.....

You do know both the KA24DE and SR20DET are both DOHC, right?

[slinds14sr20]

Check all plugs, you may have had one come apart, check the plug wires too.

[TroubleBound]

You can test if it is a cylinder misfire by removing all the plugs one at a time. When you remove the plug the car will run much worse if that cylinder was ok, if it doesnt run worse then that cylinder was misfiring. Could also try unhooking the cat converter if its clogged it could do what your describing. Itll be loud but if it runs smooth you knows thats your problem. Just some ideas..

[MisteenoMike]

You can test if it is a cylinder misfire by removing all the plugs one at a time. When you remove the plug the car will run much worse if that cylinder was ok, if it doesnt run worse then that cylinder was misfiring.

Once you do that and figure out which cylinder isn't firing, then you need to figure out if it's the plug or the injector that's not doing it's job on that cylinder.

[YuNg1's_240sx]

Yeah I do know that. Im assuming that if anyone were to have an sr swapped in, they would say sr. Not trying to argue or anything but just saying. It sounded kind of off to me.

[kool-aid54]

bluish smoke sounds like not enough spark to burn all the fuel. So my vote is a cylinder is not firing.

[liquid_cool]

you might have blown your head gasket......remove sparkplugs one by one after running your car for 5 mins max...if you notice a wet look on a plug when you pull it out..you may have blown the gasket...that would definitly make you shudder as coolant would turn to steem and vapor lock the piston on the compretion stroke..to much of this will bust or bend a rod in no time...good luck

[Explodicide]

Yeah, it was really shaky. It would shudder noticeably while idling, and it you could still feel it even at higher RPMs.

Turns out the injector on cylinder #4 wasn't firing. I replaced it with an autozone compatible, and it runs fine. The only thing is now, the car is idling at around 1,500 RPM

Is this because the ECU was compensating for the loss of one cylinder, or something? I'm going to go drive it around the block and see if the RPMs come down. If that it doesn't change, I'll reset the ECU and try again. I'll post the results.

Thanks for the help, guys.

*EDIT* Yeah, after running it around the block, the idle RPMs came back down to around 800. Smooth as can be.
Modified by Explodicide at 6:04 PM 8/1/2009

[MisteenoMike]

Glad to hear it. Hope our troubleshooting suggestions saved you at least a little bit of time hunting the culprit!