Timing issues on 425. Is my motor shot?

caddydave2001 · #1 (**permalink**) 09-06-09, 02:12 PM

Any help I can get is much appreciated. I have a 1979 with a 425 in it and its been shaking really bad at idle, so my buddy and I decided to time it this weekend. When we checked it, it was quite advanced compared to what it should be. So with his RPM/light gun, we timed the car at 23 degrees at 1600 rpms, just like the car recommends. After we got it all dialed in, took it for a test drive and the car wouldnt go over 20 mph unless I had it floored, and even then, it would lose power going up hill. SO took it back and the only way the car will actually drive decent is with 23 degrees at about 650 rpms (idle). Could this mean I have a distributer problem, the electronic module on the left side of the car is out, or is my motor shot?

We are going to do a compression test, and cylinder leak test in a week or so, but I was just wondering if this could just be a simple fix, or do I have to prepare for a rebuilt motor?

The car has always been a dog driving, but since Ive had carb issues from day one, I figured it was just dirty fuel. SO I rebuilt the carb, and put a new filter at the carb housing. Still though, the carb(after cleaning) only stays clean for about three days, and then it starts driving really bad. Something is fouling up that carb, so Im thinking I need a new gas tank, or perhaps the fuel pump is shot? Or is there another fuel filter somewhere that could be clogged?

bicentennialcadillac · #2 (**permalink**) 09-06-09, 03:12 PM

Have you checked your vacuum? Sounds a lot like broken lines or a bad vacuum break.

BRUCE ROE · #3 (**permalink**) 09-06-09, 04:38 PM

2 things to check. Make sure your timing chain is good. If its original, it should be replaced by now regardless of mileage. Those plastic teeth on the cam chain sprocket can fall off at any time at this age. The other thing is the cat converter could be blocking the exhaust. Get a newer monolithic style, which are legal and improve performance. Bruce Roe CLC # 14630

cadillac_al · #4 (**permalink**) 09-07-09, 10:52 PM

Don't these dogs require about 20 degrees of timing at idle anyway? How old are the plugs cap and rotor? How much vacuum does it have?

caddydave2001 · #5 (**permalink**) 09-08-09, 08:32 PM

Im not sure how much vacuum its making. I can feel pretty good vacuum on the line leading to the air filter. I had a full tune up done not that long ago, so most things should be fairly new. I can definately check into the timing belt and chain, because i bet they are definately original.

Where else could vacuum lines be? I have checked and replaced almost every line leading to the canister and the carb. I do have an issue which every once in a while, the ac vents go straight to the floor, and the car seems underpowered at that time, but thats about it. I know for a fact I still have issues with the carb. Could it be the vacuum is leaking out of the carb itself?

During the last few days, the car has been driving ok, but still feels quite sluggish, especially with the ac on. I know there has to be more power output and Im just not getting it. I just freaked when my buddy told me my motor might be shot. Anyone ever replaced the module that controls all this stuff? That lil black box on the left?

I will try everything posted here over the weekend and let you know. How can I know how much vacuum I have and how much I should have? Also, is there anything that typically fails on the vacuum system? My cruise works just fine, and I thought if there was a leak, it wouldnt work at all.

With the cat converter, I had the exhaust replaced but I was told the cat was still good. DO they make that big of a difference with performance?

steelybill · #6 (**permalink**) 09-08-09, 09:52 PM

The timing chain and sprockets are behind the front cover where the water pump is mounted. Don't know if that's a problem on yours. If the timing light shows the timing moving around on the balancer mark at idle., you likely have at least a loose/worn chain.
Another item could be some sticky valves intermittently. A pint of Marvel Mystery Oil might be a good idea added to the oil.
If your converter had been bad, they would likely have been happy to sell you a new one, so it's likely OK.
Don't know if your manual has info on vacuum. A vacuum gauge may be helpful. If the gauge is steady at idle, it's usually a good sign, but if it wonders around, you have something to look for.

cadillac_al · #7 (**permalink**) 09-09-09, 01:21 AM

Good vacuum will just rule out vacuum leaks and you can quit looking. Super low vacuum could indicate a clogged cat too. I wonder if the vacuum advance is working on the distributor?

Brother_B · #8 (**permalink**) 09-10-09, 12:16 AM

Although I am far from expert, I was thinking just like cadillac_al - vacuum advance at the distributor.

caddydave2001 · #9 (**permalink**) 09-10-09, 04:31 PM

How, and where do I check the vacuum? And perhaps the vacumm is the big issue, especially since there is a vacuum advance on the dist.

steelybill · #10 (**permalink**) 09-10-09, 09:44 PM

A handy tool for working on cars is a hand operated vacuum pump with the gauge on it. They are available at auto parts stores. With the hand pump, you could have the distributor cap off and apply vacuum to the canister, and see the movement of the plate in there.

Also, there are centrifigal (sp) weights under the rotor which sometimes get rusted to where they don't work. Take the cap and rotor off and inspect the guts of your distributor.

caddydave2001 · #11 (**permalink**) 09-13-09, 02:48 PM

About the guts on the distributer, we did notice that the metal arms under the rotor were very loose and a little rusty. Could these be worn out, and if so, would I have to replace the entire distributer?

Ill be doing alot of checking next week, after I get my hands on a vacuum gauge. Its been running pretty good lately, but still, it sounds like the motor is getting overworked, and still lacks punch. The timing just seems off, and it still shakes like hell under certain idle conditions.

steelybill · #12 (**permalink**) 09-14-09, 12:42 AM

There are after-market sets of weights and springs for your distributor, usually at auto parts stores. Not difficult to replace them, but if they are loose, they are likely working. I seem to remember something about a shim that belongs under your carb on that engine. Did it have one there when you had it off??
( I may be recalling the wrong engine ) Checking fuel pressure is always a good idea. The vacuum gauge set is usually made to check fuel pressure also...on some brands. You would have to remove the fuel line from the carb and check pressure there, while cranking the engine. Fuel pressure on a Q-jet should be 5 1/4 to 6 1/2 lbs, at idle, according to my manual.

daniel58 · #13 (**permalink**) 10-13-09, 02:45 AM

Just to add to the advice about checking fuel pressure. there is a second fuel filter in the gas tank on the pickup that could be clogged at times. This does sound to be more consistant, like a timing chain problem however.

caddydave2001 · #14 (**permalink**) 10-27-09, 07:56 PM

I think I found my issue for sure, but I cant for the life of me find a replacement part. Can anyone help??? Ok, there is the vacuum advance that's on the right of the distributor. I traced the hose down to an orange boot looking thing that has the vacuum hose going through it. This thing is broken off completely! There is a small shaft that is coming out of the block where the dist. attaches, and this boot pushes vacuum and as far as I can tell, it pushes this small shaft in and out. When i turned on the car, the plunger thats inside the orange boot pushed out but obviously being broken off, doesnt touch the shaft anymore. Does anyone know this part and where I can find it? This obviously has to control something, and Im positive that if this plunger assembly is supposed to be sealed, being broken off is what is causing my vacuum to leak and the car to drive like crap. Possible?

cadillac_al · #15 (**permalink**) 10-28-09, 12:05 PM

Just plug the vacuum advance directly to the carb until you can find that part if you think you need it. A lot of people threw that stuff away back in the day. Try plugging it into the vacuum port on the front side of the carb on the throttle linkage side and you should notice a huge difference.