: engine knock after hard acceleration? olds 307



cadillac kevin
12-07-10, 04:39 PM
my name is Kevin and I have a 1986 fleetwood brougham. I call it a beater due to the body damage, but its really not that bad, just all original (and I mean ALL original) I have been having a problem with the engine. It will drive down the street fine, but if I floor it or accelerate hard (secondaries open) getting on the highway, I start having issues with the engine knocking or "dieseling" (sounds like a diesel truck). The odd thing is, that I only hear it coming out of the tailpipe. I should also note that if I make a right turn doing more than 20 mph, I will get a knock from the tail pipe that lasts anywhere from a minute or so with octane boost until an unknown length of time thats really long without octane boost. without octane boost, I could park the car after it knocked, wait from 5 minutes to half an hour, restart, and still have a knock. I have had the car wound up to over 85 on the highway (during an acceleration test) and the car accelerated great, but the second I left off the throttle and reapplied at partial throttle, I got a loud knocking out of the tailpipe. The engine still performs ok (as good as a 307 can) and still has stock performance times, but like I said, whenever I accelerate hard or come out of a hard right turn (even feathering the throttle) the engine knocks and keeps knocking. once this did lead to the car dying (was knocking for a long time (probably about 5 to 10 minutes) very loudly, even during idle, started running incredibly rough after I floored it again to keep from getting a red light ticket, then had no go at all and started sputtering or surging forward under coasting. at that time, I pulled off into a parking lot, and let it idle for a minute, during which time it was running incredibly rough, until I shut it down (engine would have died very soon anyways) I had it towed to my mechanics, offloaded off the truck, and when he fired it up, it first wouldnt turn over first time, then second time, black smoke came out of the tailpipe and it ran rough and gave off smell of unburnt gasoline for about 20 to 30 seconds, then it stopped spitting out black smoke and started idling fine. That only happened to me once, and hasnt since (after that I put octane booster in it, which greatly diminished the duration and loudness of knocking, although it still knocks, but only after hard acceleration or if accelerating out of a right hand turn) I think the EGR valve is bad, but I dont think thats all thats bad.
Also, I get absolutely horrible mileage under normal driving conditions. I drive 16 miles hiway at 60mph and 5 miles on the street at 35 to 40 mph a day and average under 13 mpg. the best I ever got was 14.5 mpg per a full tank, and that was before the problems started happening. I asked my mechanic, and he said that its an old V8 so mileage will never be great, and about 15 combined mileage should be about what I'm getting. I've even tried feathering it everywhere, doing 30 on the streets and 55 on the hiway with no hard starts or stops and no romping on the throttle, and I got 13.5 mpg. Is there something wrong with the car or do I just have no clue how to drive a V8? my dad says I probably drive it "wrong" hnce the bad mileage. Also, I have driven the car hard (letting the secondaries open up, doing 75 down the highway and 40 on streets and laying in the gas when the light turns green (instead of coasting about 10 feet then accelerating) and got less than 1 mpg worse
Has anyone experienced anything similar out of their 307 olds motor, and what can be done to make it stop knocking (I've tried about every octane booster I could find). I really hope its nothing serious. I know the EGR valve is bad, which I will be replacing over the weekend, but is there anything else I should look into fixing? At the current time, a new engine is not an option since I'm still fixing what 25 years of no maintenance (oil was added to because of leaking valve cover gaskets, and that was it until I got it) thankfully it only has 65xxx miles, but I've got one hell of a running tab repair bill.
sorry for the long long post but I figured I'd lay out all the problems I have had with the engine to the best of my ability so hopefully something can be diagnosed)

sven914
12-07-10, 10:43 PM
It sounds like you have severe engine ping. Pinging is caused primarily by improper combustion; more specifically pre-detonation. Pre-detonation occurs when you have carbon deposits on the heads of the cylinders, which glow red hot. The carbon deposited will prematurely ignite the air/fuel mixture causing an erratic idle and a knocking sound.

Get a can of Sea Foam (http://www.seafoamsales.com/) motor treatment and pour it down the intake while someone revs the engine. That should take care of the carbon buildup, but to be safe, pour another can into an empty tank and then fill it with medium grade fuel.

Other things that can cause engine ping are an inadequate cooling system, over advanced ignition timing, a malfunctioning EGR valve, a partially blocked exhaust, engine vacuum leaks, and improperly routed vacuum hoses (especially the ones that go to the knock solenoid).

cadillac kevin
12-07-10, 11:51 PM
It sounds like you have severe engine ping. Pinging is caused primarily by improper combustion; more specifically pre-detonation. Pre-detonation occurs when you have carbon deposits on the heads of the cylinders, which glow red hot. The carbon deposited will prematurely ignite the air/fuel mixture causing an erratic idle and a knocking sound.

Get a can of motor treatment and pour it down the intake while someone revs the engine. That should take care of the carbon buildup, but to be safe, pour another can into an empty tank and then fill it with medium grade fuel.

Other things that can cause engine ping are an inadequate cooling system, over advanced ignition timing, a malfunctioning EGR valve, a partially blocked exhaust, engine vacuum leaks, and improperly routed vacuum hoses (especially the ones that go to the knock solenoid).
thanks for the help.
I will say that the engine always idles great. its quiet and maintains the same rpm at idle. I'm not sure if this means anything, but when I first start the car, it idles high until I drive for a bit and hit the brakes, at which time, the idle speed drops to normal. It idles high enough that I can go 15 to 20 mph with no accelerator input, but once I bring the car to a complete stop for a couple seconds, it stops idling high.
I am replacing the EGR valve, and associated hoses this weekend. I know for a fact the EGR valve is bad. I also need to clean out the passages. I'm pretty sure the engine probably has vacuum leaks because, as I said above, everything is original. all the rubber parts are 25 years old and ready for replacement. I'm 95% sure the ignition timing is also stock (like I said, nothing was done to the car mechanically until I got it. all original worn out parts)
also, how do I check for partially blocked exhaust?

also, my transmission vibrates in the first 3 gears, and shifts take forever. I have had the trans completely flushed (old fluid was black and almost like syrup), have added lucas oil trans fix (worked for a while), and the fluid is still a light red. Its not the torque converter solenoid. I just had that fixed this weekafter about a month of increasingly worse problems with occasional loss of power to rear wheels in 4th gear and horrid violent vibrations at both hiway and street speed rendering 4th gear useless) When I got the transmission flushed, for a couple months it drove like a cadillac should- silky smooth during acceleration and perfectly quiet quick shifts, no noticable vibrations or loud shift noises. but after a few months, it started making a slight vibration, and is now quite noticable, especially if you knew what it used to feel like. 4th gear is still a very smooth ride, but the first 3 gears- not so much. btw, it has a 200r4

sven914
12-08-10, 05:21 PM
The high idle is normal being a carburetted engine. About 30 seconds after a cold start, you need to punch the throttle all the way down, really fast to disengage the fast idle cam. Driving with the fast idle engaged can cause problems with your transmission and differential.

The ignition time may need an adjustment to bring it back to stock specification. There are a few whats to test for exhaust back-pressure. You can take a back-pressure gauge and find someway of tying it into the exhaust system before the catalytic converter (the O2 sensor or AIR check valve would be your best bet) or you can use a vacuum gauge and monitor the reading during idle. I would recommend the vacuum gauge because that will give you the best indication on the health of the engine.

As for the problems with your transmission; you cannot diagnose issues with a gearbox until the engine is operating correctly. Everything the engine does directly effects the transmission, and can cause it to malfunction. Third gear is direct drive, which means the transmission is no longer multiplying torque; every turn of the engine is directly transmitted to the rear wheels.

NYCOUPE
12-12-10, 08:10 PM
I tried that Seafoam and some other cleaners and my ping went away after i started using better gas.

Caddy75
12-12-10, 09:20 PM
Its funny you mention all this, my '76 FWB has made a metallic rattly noise on even light acceleration for 2 years/4000 miles when its up to temperature. If you put it in park though and rev it there is no rattle. The timing has reset to where it should be (it was off a bit) and it initially appeared to diminish a little but now its back to previous rattle.

Tried disconnecting EGR valve but that made no difference. It runs on unleaded 91 fuel, idles and starts great and apart from the rattle runs great. Fuel use is 12-13 MPH highway with high AC use. No coolant issues and no foul smoke from exhaust. Also checked throttle linkage and it wasn't that. A little camera thing was inserted into one of the cylinders thru the spark plug hole and there is carbon

At the risk of speaking too soon, it hasn't caused any other problems, so isn't it just a benign thing, one of those annoying little rattles that doesn't mean much? I don't know waht else could be causing it?

cadillac kevin
12-12-10, 09:50 PM
I checked my EGR valve, and it works fine. there is a ever so slight knock at idle, but only after the fast idle is disengaged (and thats probably because of revving the engine for a second to disengage the fast idle.) I havent had any drivability issues because of it recently. although I soon realized that if it starts knocking on the street, I can let off and it will go away after a while. if it does it on the highway, I'm pretty much screwed because if I get off the highway when its knocking, it will only get worse (at least for many minutes, unless it decides to go away. I havent had the knock make the engine die since I used octane booster for a month and a half.
I will be using sea foam after I replace the plugs and wires (original wires and POS champion plugs) I figure I'll change them out in order to ensure a better spark before I clean out the carbon. I'm sure the engine is full of carbon since it had the original plugs in it for 25 years.

deVille33
12-13-10, 08:34 AM
At the risk of speaking too soon, it hasn't caused any other problems, so isn't it just a benign thing, one of those annoying little rattles that doesn't mean much? I don't know waht else could be causing it?

Detonation will cause pitting on the tops of your pistons and cause burn through the aluminum, which will give you a dead cylinder.

Caddy75
12-13-10, 04:04 PM
How do I know if it is actually detonation?

sven914
12-13-10, 06:05 PM
^Detonation usually gets worse as the engine reaches operating temperature. Most of the other noises will go away after the engine had warmed up for a few seconds. Also detonation is one of the only engine noise effected by ignition timing. So clean the induction with Sea Foam, reconnect the EGR (that stops detonation), and see if the problem goes away.

cadillac_al
12-13-10, 07:29 PM
It sounds like a possible burned valve to me (usually #8). I would do a compression check before sinking any more money in it.

Caddy75
12-15-10, 08:19 PM
With detonation though, isn't it common to see chipped porcelain and other damage to the spark plugs? None of my plugs are showing any damage or issues at all.

cadillac kevin
12-15-10, 09:45 PM
with my caddy (which as noted above has bad detonation under heavy acceleration), the spark plugs weren't chipped. my caddy had the original spark plugs in it (65xxx miles/ 25 years) until 2 weeks ago. there was no chipping of the porcelain or other damage other than excessive wear from 25 years of use (abuse.) mine were rusted, tarnished, covered in oil (car had 2 leaking valve cover gaskets) , and 1 plug was burnt, but they were intact and still working (elfin magic I guess) .