3kelvin

This is a rather long tale of woe ... and one of those "why is my engine making that weird noise" questions. It is also very weird .... never ran into something quite like this before.

So .... I bought this 1992 Firebird (305 TBI) and when I picked it up it ran fine. Nice and responsive. Drove it to work ... no problems. Well, on the way home it began making hideous noises (rattling and squealing at low RPM) and eventually stalled out at a traffic light. Restarted with difficulty ... Just to be safe I had it towed back to the house.

Now, the service engine light was on ... hooked up my laptop and saw that I am getting a VSS (vehicle speed sensor) error, which made sense since the speedometer wasn't working. We traced some of the noise to the AIR injection pump, which sounded bad when turned by hand. (The drive belt was also splitting .... so confident that was an issue.) Replaced that ... rattling and squealing gone. But now I am hearing a clanging sound. A real loud one. And I hadn't heard it before ....

I isolate that to the passenger side rocker arm cover ... I can feel it vibrate. So I pop that off and everything looks fine. When I removed the rocker arm cover, I of course detached the 8,4,6 and 2 spark plug wires (passenger side). I started the engine ... no noise. Valve operation looks fine. Decent oil pressure. (Mess.) Now, I had discovered that the EGR control solenoid was just hanging loose right next to the rocker arm cover, so I theorized that was my culprit. Put the cover back on. No noise. Cool. So then I realized I had left the spark plug wires off and re-connected them.

The clanging noise is back! Take the rocker cover back off, and with all 8 cylinders firing I still get noise. So I start popping plug wires off one at a time ... I eventually demonstrate if I connect any ONE of the 8,4,6,2 plug wires back, the noise stays away. If I connect any TWO of the plug wires, the noise returns. The number of cylinders firing seems to be produce the noise ... not which ones are firing.

Stethoscope usage puts the origin at the noise at number 4 or possibly number 6 cylinders.

So ... what is this? Why would adding cylinders (power) cause this clanging noise to suddenly show back up? Is it a function of adding power? Or am I looking at actual detonation? If it is detonation, I would expect it to go away when I disconnected the offending cylinder.

Thoroughly confused. Thoughts appreciated!

torque_is_good

I would need to hear it in person. Don't let the number of cylinders connected be a distraction. You need to connect the plugs and locate the noise

I have no clue what a clanging would sound like in an engine. Is it a knock, a tap????

3kelvin

Thanks for the reply. At idle, this is happening about twice a second. If you took a ball peen hammer and tapped the head, you would get a similar sound ...

I gotta think this has to be valve train or rotating assembly related .... but I don't see why the number of connected plug wires matters.

Groan. Wimper. I think this is leading me towards removing the head. Well, before I do that I better measure compression and cam lift just to have baseline numbers. (Really hoping I don't have to replace the cam in this thing ... ) I should probably try adjusting valve lash first before I go tearing the engine apart, but I don't think that's it.

torque_is_good

I would need to be there. Some folks mistake an exhaust leak for a mechanical sound. You need to eliminate what it isn't in order to determine what it is. With the engine off, get a lit cigarette and slowly blow smoke around the header pipes (you don't still have exh manifolds do you?) or heaven forbid, around the restrictive stock, awful exh manifolds. pay attention to the behavior

then, with someone behind the wheel, have them hold the vehicle at around 1000 rpm's and again slowly blow smoke at the exhaust. look to see if the smoke is whisked away a bit. If so, you have a leak

AutoRoc

iTrader: (1)

Maybe a lifter problem, produces some werd sounds and can be intermittent. Watching the valvesprings and rocker arms would help but you said you did that already.

///DAN///

iTrader: (1)

on my old monte carlo the heat riser in the pass side manifold was flapping real bad , sounded like the motor was coming apart I tied it open and it went away.

3kelvin

Thanks, torque_is_good. Good suggestion and I will give that a try. (Just got this thing and it has **shudder** stock exhaust manifolds. Identical to what used to be on my 91 RS. They have to go ...)

3kelvin

Thanks also, Dan and Auto_roc. Valve action looks OK but I am still wondering about the lifters .... And the suggestion about the riser ... I hadn't even thought of that. I really appreciate the help ...

I'll be sure to let ya know what I find. Thanks again.

rough

Any chance you took out the plugs and checked them out? Maybe mixed up some wires ? or a wire?

ASE doc

I don't mean to be a sooth sayer. You have recieved some good input and hopefully you'll find something external causing the noise. Another external cause for what sounds like a rod knock is a cracked flex plate. That being said, the test you describe-pulling plug wires to isolate the noise- is the very test we use for locating a rod or wrist pin knock. By the sound of your test results, you've found a bad wrist pin(clanging sound) on either 4 or 6. Sorry.

3kelvin

Hi ASE doc ... the problem with guys that start with a phrase like "I don't want to be a sooth sayer ..." is that they often wind up saying the sooth.

No sign of an exhaust leak. Riser ... doesn't look like there is anything over there that could do this.

This is a very loud sound. I can feel the rocker arm cover vibrate in time with it. And like I said removing the rocker arm cover does not affect the sound. Something has got to be hitting ... and hitting real decisively ... Looked for external stuff and have found nothing that could account for this. Will keep looking for a while but I suspect you are correct ...

I've had the oil pan off a 91 Camaro and from what I recall the prospects for fixing this with the engine in the car look slim. Hard to get at the rod cap bolts and probably impossible to set torque accurately ... any thoughts/suggestions on that?

If I am yanking this engine, I am going to tear the whole thing down and rebuild it.

Thanks for your response, Doc.

3kelvin

Hi rough ... double checked the spark plug wires and they are correct. Base timing was a little off but correcting that had no effect on the problem.

So ... I tried something else. I increased RPM to about 1600 ... and the noise basically went away. I say basically because I think I am still getting a hit once every 15-30 seconds or so. When I remove plug wires, that has the effect of lowering idle RPM ... so this seems to happen in a fairly narrow RPM range.

I guess my question is ... does this support ASE doc's theory about the wrist pin?

3kelvin

OK ... I think I know what it is. On the suggestion of another friend, I stuck my head down near the oil pan. Deafening. Much louder than on top. His theory ... the bearing is gone and the rod is essentially cutting a groove in the crank. The sound I am hearing is the rod slamming into the crank now that enough clearance has been created to let it wiggle as the assembly rotates. Above a certain RPM, he claims, the effect is somewhat relieved ...

So ... it looks I'm looking at a rebuild or a new engine right away. Rats.

Thanks to everyone for their advice ...

ASE doc

Bummer. Your freind is right about rod bearing noise. It does change with rpms. I said wrist pin because you mentioned a clanging sound and can feel it in the valve cover. Rod bearing tends to be a deeper "knocking" sound. Either way, it sucks. Of course, rod bearing sucks much worse because it involves a total teardown and probably a new crank. If the bearing is gone or even badly torn up, be sure to thoroughly clean the block to remove all bearing material. Don't want it to end up in your new bearings.

Denis.V

According my experience, I vote for groove in the crank or mixed spark plug wires...


Denis V.

torque_is_good

what stinks here is most rebuilds consider re-using the crank. Hopefully the block is also salvageable. It might be time to also consider a long block depending on what machine shops charge in your area for rebuilds. Only you can make the cost/benefit analysis but can't do that until you have all the information.

good luck

servo2055chevy

You know. I have the same problem! I haven't gotten as far as you have with it by checking the egr and whatnot but. Its like a ticking, and I hear it from the passenger side of the engine. My oil pressure does hang low when warm, Never in the red though but the line above it. I use 10W-30 Oil. The oil pressure goes almost to the line above 30 on the oil gauge, but I still have the noise so I suppose it couldn't be an oil thickness problem... I was told it's coming from the bottom end of the engine and to use a thicker oil but I did that and It make little difference in oil pressure and that ticking is still there. Then I researched that the lifter rods are hollow on the inside for oil to come up to the valves and rocker arms and if that is clogged with sludge then thats why its ticking. So I have been using some seafoam in the engine oil to clean it out and nothing is helping. Thick, Thin oil, Cleaning. Help please. Also my pcv valve is popping up half way sometimes in the drivers side valve cover. The car used to burn some oil at startup but I have been using mobil one high mileage oil and it went away for the most part, but recently I have been burning alot of oil (no smoke) but Id have to add almost half a quart like every 2 weeks or so. and when I floor the car I smell burning oil bad (no I don't always floor it, I just wanted to see if the pcv valve would pop up after pushing it back in. Also I read someone posted on this thread about inserts for spark plugs?? what are they about? Thanks for the Help!
Also. I too was told it was an exhaust leak at that bank of cylinders by the header pipe

ASE doc

The anti foulers go in with the spark plug and surround the tip so that they are not so exposed to oil in the cylinder. They extend the life of spark plugs in engines with heavy oil cosumption.

To find an exhaust manifold leak, use a length of 5/8" heater hose held to your ear to trace the joint between the head and manifold. You will clearly hear a leak as you pass the end of the hose over it. Also, look carefully for cracks in the casdt manifold and check the joints between the manifolds and exhaust pipes.

3kelvin

Sorry I haven't gotten back to you guys. It has been a crazy busy few days, and a very close friend of mine has been having some serious medical issues. Again, I want to thank all you guys for lending me your knowledge and advice. I am looking at the whole range of alternatives ... the odds are I will probably rebuild the thing. Or drop in a 350. (Did that with my 91-RS ... kinda wanted the 305 'cause it is easier on gas. Decisions.)

I want to share one thing with servo2055chevy. Before I swapped my Camaro's original 305 out, I was having similar oil pressure gauge behavior. Engine was running great, but oil press was scary low after warm up. I was giving the engine a real short life expectancy at that point. But I thought I should verify the oil pressure with a mechanical gauge before doing something serious .... so I was going to remove the oil pressure sensor and screw in a hose for an oil pressure gauge I had borrowed. When I disconnected the oil pressure sensor, oil was all over the connector! The sensor itself had failed and was leaking, causing it to read low. New sensor, and suddenly my warmed up engine was reading around 15 psi/1000 rpm ... small block chevy needs at least 10 psi/1000 rpm, of course.

Oil pressure sensor is a cylinder that screws into the block on the driver's side, not far and from the oil filter.

I would check it out before doing anything drastic.

Again, thanks everybody. I will post my progress and anything else that might be useful.

servo2055chevy

Hey thank you. I appreciate that. I hope everything goes ok on your end too. Now is there any special tecnique to changing that sensor???

ASE doc

Allow me to interject here. Your 88 may be different from 3kelvin's 91. His oil sender in on the side of the block but yours is more likely below the distributor on top of the block at the rear of the intake manifold.

servo2055chevy

It's not... Atleast i'm pretty sure it isn't. I have seen it before on top of the oil filter. Unless it was the knock sensor on the opposite side of the block hahaha, i'm not sure. I will find it. What would it look like if it's under the distributor? And is it hard to get to and replace? and most important, expensive???
Thanks

InfernalVortex

iTrader: (4)

Some time between 88 and 91 they switched to an integrated oil pressure switch/sending unit above the oil filter. Before the switch they were separate units, and the oil pressure sending unit was beside the distributor in the rear china wall.

ASE doc

It wouldn't be the knock sensor. Knock sensor is midway between front and rear of engine, passenger side. If it's below the distributor, it's tough to get at. Almost better to pull the dist. Pulling the dist is no big deal for me. I do it all the time. Just remove the cap, mark position of the rotor on the base plate with a felt tip marker, and note movement of rotor as you lift distributor out. When your done with the oil pressure sender, Place the distributor with the rotor in the same position as it was after you lifted it out, and lower it into the hole. If you have it right, it will drop in the first time. You'll want to reset timing when you're done.