joe350

My base timing with the EST wire unplugged is about 6.5* BTDC. As I rev the engine up slowly the timing retards to about 5* BTDC and then at a certain RPM (unknown, but probably between 3-3.5k) quickly jumps up to about 14* and sticks there until I lower the throttle. I suspect a loose timing chain to be the culprit for the first problem but I have no idea why it would suddenly advance in timing with no computer controlling it. Possibly a bad distributor? Please I need advice on this one as my experience is low in this field. Also I'm pretty sure the loose timing chain would cause my roughness of idle, but I would like someone who has experienced this to chime in and give me their opinion.

Thanks

iroczracer07

iTrader: (2)

The timing chain could be the problem, but the bushings in the distributor have also been known to cause the timing to go all over the place. I would pull the distributor and check that before I tore down the motor to check the timing chain. Usually timing chains jump a tooth when they're worn out, which causes the rough idle. Sometimes they even snap, causing a no start condition. Distributor bushings cause irregualr timing shift when they're worn out. So my money's on your distributor.

Vader

I'll second that. The timing should be flat with the EST disconnected. Look for axial play in the distributor as well radial play. The shaft may be climbing the cam gear if oil pump resistance is changing under load and the oil pump drive is worn/rounded over.

Besides, HIS money is on your distributor, and it might just be enough to buy a replacement bushing set.

joe350

With 120k miles on the engine, I suspect both timing chain and distributor playing a part in this matter... mostly because I've checked or replaced almost everything else. So to check the distributor should I look for it to move in any way with the hold down clamp on, or take it out and check it that way? I know a new distributor cost about 100 bucks. Would replacing just the bushings be that much cheaper/easier?

joe350

Initial tests on my distributor do not reveal any play but I don't want to damage my cap. I suppose I'll remove it soon and check it more thoroughly.

I'm trying to look at my rough idle issue objectively but thereis always the factor of wanting what you think the problem is to be the problem. I really think that this unusual timing issue combined with my vacuum flutter (fluttering between 19.5-20.5 or so in/hg at idle) indicates valve train issues, most likely a worn timing chain. I also know that there is always the possibility of multiple problems... which I have had in the past. I've been dealing with bad idle issues for about a year now and I just want it to be done with.

Damon

Are you using an MSD box or similar? Some timing lights don't work accurately if used with a multi-strike ignition box. The problem seems to be that sometimes they fire the light on the first strike, sometimes they fire it on the last strike of a multi-strike sequence and often there will be an abrupt change in timing reading when the box switches from multi-strike to one big wollop (around 3200 for an MSD). One of those little things I've seen so many times I can spot it instantly. But if you've never seen it before it can drive you bonkers.

joe350

Nope, 100% stock engine.

Guest

The distributor module adds some timing at a higher RPM, thats why you're seeing 14.
New plug wires? Plugs? Grounds ok?

iroczracer07

iTrader: (2)

Thanks a lot Vader!

joe350

I've checked or replaced nearly everything in the fuel injection system and ignition system. The distributor itself is the only thing I have not replaced in the ignition system. I've checked for vacuum leaks and cleaned everything out. So you are saying that the distributor will add timing by itself with no input from the computer?

Also, timing is a bit jumpy with the EST wire connected. I don't see why this would happen. Basically it jumps between approximately 16-20* BTDC at idle. Is this normal? With the wire connected it varies by about 1/4 degree each way from 6.5* at idle and slowly retards to about 5* as I increase throttle until it suddenly advanced to 14*. Could this difference in timing be causing my rough idle? I don't think its the problem though because my idle is still rough with the EST unplugged.

How loose does the timing chain have to be to cause rough idle?

How bad does the distributor have to be to cause rough idle?

Basically, I really don't want to replace one or both and have them not be the problem.

iroczracer07

iTrader: (2)

a worn bushing will cause the timing marks to jump back and forth while you're trying to set the timing. a chain usually causes a severely rough idle or a no start if the chain has jumped too much or broke.

88305tpiT/A

iTrader: (2)

The module inside the distributor adds a fixed amount of timing (like 10 degrees or so) at a fairly low rpm. I think its around 900 RPM where this 'jump' in timing happens with the EST unplugged. plugged in the module takes input from the ECM and converts it into advance. It usually jumps around a bit like you describe.

The not so stable timing you describe with the EST unplugged is probably slack somewhere in the system between the crank, timing chain, camshaft, distributor gear, or pickup coil.

joe350

Even still, the slightly unstable timing wouldn't hurt my idle. I'm worried about this being a symptom of another problem. The idle is rough, but not extremely rough. The car was still running with two injectors shorted, a bad fuel pump, and whatever the problem is now all at once.