About to Push it Into a Lake... AFM/Idle/Stalling Issues

[Deepa]

Gentlemen I'm at my wits end here, any help or direction would be extremely appriciated, willing to investigate anything/everything.

I purchased a '92 SC400 a few months ago, car looked good, ran okay and was generally clean. First things first, I did a full tuneup (caps/rotors/plugs/wires/fuel filter/air filter.) The car ran great, strong, no CELs. No problems. On go the 19's, Konis, Pro kits, Recaros, etc. I'm happy.

About 4 weeks ago a buddy asks to borrow the car to run errands as he sold his to go work in the UK for a year. No problems, trustworthy guy, etc. Well in the first 15 minutes he sideswipes a GMC Safari at about 30 kmph, pushing in my passenger fender, bending the rim, and scraping the door. He said he stopped, exchanged info and then as he was pulling away (fender cutting my new rubber) the car just died. He started it up and drove a few feet and it died again. Had the car towed to another buddy's shop.

So, I show up the next day, crank it a few times and it will start, but the idle is crap, lots of misfires, low idle and very slow to rev, only revs to 1800, won't go anywhere in drive, stalls right away. A quick look around and notice there's next to no gas in it. Great. So I go get gas, throw in 25l and no change.

I did a few hours of reading here and the AFM looks suspect. I unplug the AFM and the idle smooths out, but not much, maybe 50% better. At this point I go get a used AFM, plug it in, no change. I figure I probably got a bad one and order one from the States. Three weeks later I get the AFM, stoked I can drive again, plug it in, same issue.

One thing I did notice was that the car ran only slightly better with the AFM unplugged, others advise the car runs fine without, albeit a little rich. Does not drive well at all without it either, won't rev up accelerates with much trouble, getting to 40 kmph is impossible.

I did check for spark and fuel pressure is good. I tried a spare ECU that was working well in the previous car. Also tried both ignition coils. No changes here. I also tried pulling codes, all I got was 29 for a bad sub O2 sensor, I replaced both, no solutions here. No other codes in memory, but that 29 still pops up after a reset. When I took the fender off, I looked for any damage to wiring, didn't see any. Didn't see any unplugged/broken connectors either.

If you've read all of this, thanks again, and please HELP MEEEE!! I've posted on other sites that I frequent but no help available it seems. If anybody is wondering why I don't just go through insurance, the reason is that the other driver apparently didn't care about a new dent in work van and didn't want the hassles. So I hear at least.

 

[och]

Sounds more like your ignition is bust. Usually one of the ignition coils die, and then the car will run on four cylinders, and run like crap.

Unplug the coils one by one, see if it runs on one of them, and replace the other one.

Also, see if your cats are glowing red, if so thats defenately the coil.

 

[Deepa]

That was quick, haha.

I had tried a spare pair of coils and didn't see a difference so ruled it out. Could it be both the afm and a bad coil? Now that I think back, I didn't unplug the afm with the new coils so I don't know if there was an improvement.

Is there a way to test both, bearing in mind that the car only idles for 30 seconds or so at a time?

Another thing I was wondering, is it possible that when my boy swiped that van it shook something loose causing something to ground out or a short from the impact? Anything that's known to be fragile?


Thanks, and btw, whatever happened to your issues? Read about them while searching.

 

[och]

That was quick, haha.

I had tried a spare pair of coils and didn't see a difference so ruled it out. Could it be both the afm and a bad coil? Now that I think back, I didn't unplug the afm with the new coils so I don't know if there was an improvement.

Is there a way to test both, bearing in mind that the car only idles for 30 seconds or so at a time?

Another thing I was wondering, is it possible that when my boy swiped that van it shook something loose causing something to ground out or a short from the impact? Anything that's known to be fragile?

Oh, my bad, missed out the part in your post where you said you replaced both coils.

In any case, you could have got some weird short or pinched fuel line from the accident, or maybe there was a connector/sensor that was on its last breath and the accident shook it up. That wont be easy to find.

I would still start to see if the car is running on all eight or only four cylinders, by trying to start it with only one coil connected. If it runs on one but doesnt run on another, that means you're running on 4 cyls. If it runs on both, yet even worse than it is running now (twice worse) then you are running on eight cylinders, and it would be a good time to inspect timing belt and distributors.

Thanks, and btw, whatever happened to your issues? Read about them while searching.

Absolutely nothing happened to them, they persist. :banana:

In fact my other car is acting up as well now

 

[Deepa]

Okay, so I pulled out the coils and inspected them again, one has a crack along the bottom, so I replaced both and cranked the car. It started up stronger, seems less of a misfire but only about 30% better. Still idles crappily with the AFM UNPLUGGED and refuses to smoothly rev up. Still dies when I plug in the AFM.

Trying to source an AFM now. :worried:

 

[och]

I doubt if its the AFM. Its just that your ECU sends more fuel to the engine when the ECU is unplugged, because its in open loop.

Sounds like the car is starving for fuel. Check you fuel pressure. I know you said in your previous post that you checked it, but did you check it with a fuel pressure gauge? Because fuel pressure in our car is suposed to be pretty high, around 40-50psi?

 

[spf_lexus]

when I supercharged mine I unlocked quite a bit of fuel flow when I replaced a neglected fuel filter... engine revved much more freely w/ much less hesitation. Mine was an extreme case tho, it looked like black oil coming out of the filter, worth a try.

 

[Deepa]

I was thinking about the gas I found on the plugs before, that it may have been because the coil was screwed and not because the car was running rich like I had originally assumed. I will check the fuel pressure again to see if its within spec.
I did a search and learned about the dual speed pump, I have a spare unit and was gonna try that as well.

Thanks again for the help bro, all good advice so far!

 

[Deepa]

when I supercharged mine I unlocked quite a bit of fuel flow when I replaced a neglected fuel filter... engine revved much more freely w/ much less hesitation. Mine was an extreme case tho, it looked like black oil coming out of the filter, worth a try.

I had done that as preventative maintenence a few month ago, but thanks, any thing is worth looking at for me right now.

Along those lines though, did you find the stock fpr to be troublesome?

 

[spf_lexus]

nope, don't even have it anymore... used to run a rising rate FMU, and the stock one just wasn't needed.

I suppose the rubber diaphram inside yours may have failed? I spent 6 months chasing a bad misfire on mine and found it was fouled plugs all along.

 

[Deepa]

So... it turns out the timing belt had jumped 4-5 teeth.

I had checked the timing marks when I first started looking for the problem and I must've done something wrong because when I checked it the other day, it was way off.

After fixing the timing belt and some new plugs, the car runs very nice.

Any ideas how this might have happened? The tensioner was replaced when we did the timing belt.

 

[spf_lexus]

If the belt had some slack it could have jumped teeth, otherwise i would be interrogating my builder or the last guy that wrenched on the T-belt. If the tensioner is torqued to spec there should be no way for it to jump. Only freak accident way that I can think up would be tensioner bolts coming loost allowing belt play... but thats a far streach. Did you re-use an old belt? Sometimes the marks get worn off and the process of installing the belt over passenger side pulley can cause slack of a few teeth.

Good to hear it's sorted... drives like silk no?

 

[Deepa]

Well I'd be blaming me in that case, haha.

I replaced the belt, tensioner and idler bearing and the car was running perfectly fine before this incident.

Car runs great again (aside from an exhaust leak now,) just hoping this isn't something I need to go through again anytime soon.

Thanks again for the help you guys provided.