Engine Knock / Ping - Toyota Nation Forum : Toyota Car and Truck Forums

jamesjk · 03-24-2006, 04:42 PM

Hey all, this is my first post here. Thanks in advance.

I just bought an '87 corolla (4A-LC) to drive to the park and ride and after owning it a few weeks it developed a nasty engine knocking pinging sound all of a sudden. I have had two of my mechanically enclined friend listen to it and they all agreed with my assesment that it was pinging and not a berring or other mechanical failure.

I replaced the timing belt because it was due for a new one anyway, but that didn't help. The timing is spot on: 5 degrees BTDC with the vacume hoses disconnected from the distro and 13 degrees with them connected. I'm using 89 octane fuel and I performed a full tune up about a week before this started happening: oil, plugs, cap, rotor, filters, pcv valve.

The sound is only produced when the engine is under load. If it's out of gear and you rev the engine, it doesn't make any bad sounds. However, if you accelerate at all when driving it make the sound... the harder you accelerate, the louder the sound gets.

Can anyone think of any other reasons why an engine would knock like this? Carb issues?

Thanks!

igorien2k · 03-24-2006, 10:39 PM

it might be running lean. so yea carb

***REN69*** · 03-24-2006, 11:35 PM

bad plugs/wires causing cylinder misfire maybe. I had that problem before, one of my wires was grounding due to having a cut on it and basically would make my car run on 3 cyl.

jamesjk · 03-25-2006, 11:19 AM

I guess I could get a new set of plug wires for pretty cheap. I hadn't even considered that. If it was running on three, wouldn't it smell like gas? As for the carb, any way to confirm the lean theory?

jamesjk · 03-25-2006, 07:31 PM

I got new plug wires, but that didn't make any difference. I think I'll take them back. I'm starting to think it may be a problem with the carb. Maybe it's the accelerator pump? I've heard that you are supposed to be able to see a jet of fuel when you turn the throttle, but I can't see anything. Anyone know where exactly this jet is visible inside the carb?

Flashmn · 03-27-2006, 12:25 PM

A dead accelerator pump wouldnt cause a lean condition all the time, it would only cause a bog when you quickly floor the accelerator.
I doubt it would be the carb if anyone hasnt messed around with it. Secondly, listening and hearing pinging isnt easy, its very likely to think its pinging even if its not.

jamesjk · 03-28-2006, 04:36 PM

I read in another post that a stuck open or malfunctioning EGR valve can cause knock. The more I think about it, you're right about the pump.. that would only matter in bursts. I still think it's running lean because it doesn't do it when the choke is on when the engine is cold. As soon as the choke opens (not choking) it starts doing it. Since the choke richens the mix, I think it is counter-acting the issue. I'm going to check the EGR. Maybe I could try rigging the choke on to test my lean/rich theory?

jamesjk · 03-28-2006, 11:37 PM

Well... the EGR is totally clogged with carbon deposits. It is so clogged that I cannot even burrow a passage through the carbon. What happens when these things clog up? It can't be ideal, but could this really be responsible for the knocking and poor performance? $150.00 for a new one. Maybe I can find a salvagable one at a junk yard.

Psycho_rolla · 03-29-2006, 03:19 AM

sounds exactly like what i had i was running 98 octain in my corolla with the new motor the fuel prices blew out and ened up using 90 octain insted i jus ajusted the timing on the car till it didnt ping any more under load

Cheers
Ben

jamesjk · 04-05-2006, 01:12 AM

I gave in a took it to a machanic. It turns out the carb has been running lean which has burned up the exhaust valve in the #2 cyl. Now that cylinder only has 30 psi (instead of 150). The lean mix and dead cylinder are causing the ping / no power.

Now I have to decide if I should:

a) Scrap it / sell it for cheap
b) Engine swap
c) Rebuild it

What engines can you swap with the 4A-LC FWD ?