My Dad and I are still trying to get his 86 to run after the broken valve spring. While changing the spring we had to turn the engine over w/o the distributer installed so we lost track of where everything should be when back together. We followed the book's instructions for putting it back together and it won't run - we also had to replace the MAF relays and now it runs really rough.

The big "If" we have is that there are 2 marks on the balancer a deep one and a shallow one about 45* apart. We used the deep one for the reference for the distributer and valve adjusting and when the distributer is installed pretty close the engine will not run at all and occasionally backfires on cranking (exhaust I think). We got the engine to run (poorly - but it did run) when the shallow mark was close to 6*.

Question 1: Why are there 2 marks?
Question 2: Which one should we be using? We used the deep one on my 90 and it runs great.

It kinda sounds like I am answering my own questions here but I need someone smarter to step in before we re-adjust everything for the small mark.

Please Help!

Dale

 

If the damper is for a 400, it may be marked for a different timing pointer location. I would buy a piston stop and a timing tape and eliminate all future problems, once and for all. Good luck, and...

RACE ON!!!

 

Here's another way. You can try the "finger in the #1 spark plug hole" or "rolled up paper towel in the #1 hole" trick.

Remove the #1 spark plug. Stick your index finger in the hole and have your Dad bump the engine. When you feel pressure building the #1 piston will be on the compression stroke.

Now look down at the harmonic dampner and one of the two grooves should be closing in on the TDC mark on the timing tab. That'll be the one to use as reference when setting the initial timing.

If you're alone, just roll up a piece of paper towel and stuff it into the spark plug hole; when it blows out during bumping, the piston will be approaching TDC on the compression stroke.

Mark that groove with some fingernail polish to be able to later distinguish it from the other one.

Now that we've identified which groove to use, the problem then becomes whether the timing tab on the timing chain cover is the correct one for the dampner you're using.

If your dampner is of a non stock diameter, you'll need to get a timing tab designed for the diameter of the dampner you're running.

Be sure to disconnect the EST wire when you're setting the initial timing to 6 degrees BTDC and clear the error code by disconnecting the battery after you're done. A code will set when the ECM detects the engine running with the EST disconnected.

Hope this helps.


[Modified by JAKE, 3:53 PM 4/17/2004]

 

OK, we used a wood dowel and a finger in the hole to find TDC - it was the big groove. We got it to start and timed it to 6* BTDC (EST unplugged and at 7-800 RPM) but it runs terrible.

We put the vacuum gauge back on and while running it is violently jumping from 3-8in. Cranking vacuum is jumps from 0-1in.

Now what did we mess up? Here is a link to what we did before http://forums.corvetteforum.com/zerothread?&id=771612

Please Help

 

I forgot to mention that I plugged off all vacuum lines (Power Brakes, EGR, HVAC) and ran a known good line directly to the FPR and it still acts the same.

 

If you can get it to run, with it running pull a plug wire off. If the RPM's don't change then something with that cylinder is wrong. You may find 2 dead cylinders and have crossed up a plug wire somewhere. Or maybe something with the injector with that cylinder is goofed up.

At least you will find out which cylinders are giving problems.

 

There could be one (or more) different causes for this; it's just a matter of tracking it down by checking everything. Yep, you've got to start over, from the beginning and check everything again.

Don't take ANYTHING for granted (like I read some guys post words to the effect "I know that - such and such - is okay; blah, blah, blah." You must re-check everything; the magic fairy isn't going to visit your engine over-night and repair the problem.

You didn't mention it but after setting the intial timing, did you shut down the engine, disconnect the battery, plug-in the EST connector and start it back up?

If so, the timing mark on the dampner should now be near the top of the scale on the timing cover tab. If it isn't, either the EST is not connected or the ECM (computer) is bad. I had a failed computer once that prevented the ECM from taking over the ignition timing.

Connect your timing light to each plug wire one at a time and make sure each one shows a steady flash.

Double check:

Plug wire(s) are not connected to the wrong cylinder

All vacuum lines are either blocked off or connected; there's one under the
Throttle Body on the driver's side that sometimes gets missed. TPI engines are very sensative to vacuum leaks.

All sensors are connected; MAF, IAC, TPS, engine coolant at front of manifold, air temp sensor underside of plenum near distributor.

Disconnect the MAF connector and see if the idle improves, if it does, the MAF is bad.

One of the lifters could be tightened too much (excessive preload); this will cause a terrible idle. This a very common problem with those who haven't screwed on these suckas for a long time. There's a procedure I posted on this Forum in the Tools section that gives a step by step that I've used since Hector was a pup. There are other ways to do it, each to his own I say.

Look for any spark jumping from the plug wire(s) to ground; a darkened garage works best. Also, listen for little "pops" that can indicate ignition spark jumping to ground.

Keep us posted. Hope this helps.

Jake

 

Update - We followed your advice and double checked the valve adjustment and found one that had way too much preload. That solved the problem of the jumpy vac. pointer but now the gauge reads a steady 8in at 800 and will not run without some gas pedal.

We also disabled the spark and Dad blocked the TB with his hand while I ran the starter. When I stoppped, the car held 5in until the hand was removed - this leads me to believe that there are no signifcant leaks in the intake system. We did the same thing to the 90 and it held 4in. Does this make sense?

Some of our books mention that a low vac reading can be caused by late timing. We set it to 6* per the label. Should a 383 with a 219 cam (I think) be set different or would it not make enough difference?

We're getting closer...

 

6 degrees of initial timing advance is the base (stock) setting. You can play around with that setting to see if you get better performance by increasing it.

If you go much above 10 degrees you'll begin to get a lot of spark retard and knock counts. You won't be able to tell, though, without a ScanTool, Diacom or some other program that can log that data.

I have no idea about the "hand over the TB while cranking the engine" etc. Never heard of that as being a test procedure for detecting intake leaks.

The engine should pull much more vacuum at idle with a 219 camshaft. It should be 12" at the minimum and probably more.

The late timing indication that you see on the vaccum gauge should be ignored. It's meant for stock setups, not performance camshafts. A performance camshaft will not pull enough vacuum at idle to move the needle out of "late ignition timing" area.

Where are you taking the vacuum reading from?

You didn't mention anything about timing after the engine has run for a few minutes. The ECM should be taking over the timing and the timing should advance up to about the 20/24 degree range once it does. This would put the harmonic dampner mark up at the top of the scale.

If the timing is remaining down in the 6 degree area at idle, then it's the EST connection or the ECM that's not allowing the timing to be controlled by the computer.

Remember, I believe I wrote about how the timing circuit in my 86 died a few years ago and the timing could not be controlled by the computer. I discovered the problem when I swapped in a friend's ECM and the engine perked up like you wouldn't believe.

The other things still much be checked.

Disconnect the MAF to see if the engine running improves.

Check and adjust the TPS voltage setting

Re-Set the IAC using the paper clip in the A&B terminals of the ALDL

There should be instructions of doing this in the "TOOLS" section on this Forum.

I'll try to help you guys out as best I can, but I do need to know the specific details of what you've done or tried. Without knowing, I can't make relevant suggestions.

Jake

 

Sorry it took so long to respond but the car is running again. Turns out when I replaced the power and burn-off relays, I got them messed up. I discovered this when I would unplug the MAF the computer would not throw any codes. We also bought a new MAF that made little difference.

Now for the next hurdle. It has an irregular/intermittent miss accompanied by loud exhaust popping. This happens mainly under load but it does pop at idle a little.

I noticed that one of the AIR tubes in the header has a small rust hole (cheap LPE coating). I think this might explain the popping but what about the miss?

Thanks for the help!

Dale

 

The miss could be simply arcing of one of the plug wires to the exhaust manifold or valve cover.

Do a dark garage check with the engine idling and check each wire, one at a time, for signs of a spark jumping to ground.

Spark plug boots that are close to the exhaust manifold are a common spot for this to happen.

Spark plug wires should be separated by at least 1/4" - more is better. Use wire separators or fashion separators out of plastic tie wraps (cable ties) to maintain clearance between the wires.

The next thing I'd check would be the spark plugs. Check them for proper gap and look closely to see if, perhaps, one had gotten cracked during installation. You should see a tiny hairline crack in the outside porcelain if it's cracked.

Also check that they are properly tightened.

Jake





[Modified by JAKE, 9:18 AM 4/29/2004]

 

Do you still only have 8 in of vacuum? Something is wrong there if you do. As Jake mentioned, it should be well over 12....more like 16. You sure the valves are not too tight. I once tried TPIS' suggestion of three turns preload and it ran like you descride. Went back to 1/4 turn and it was fine. Do all the cyls have compression?

Good luck.....sounds like you are at least making progress

 

You're right, Ralph.

8" is still too low. If it's still at or even near 8" something is still amiss, unless you guys are running a very long duration camshaft.

What cam's in the engine?

Try plugging the exhaust leak with some JB Weld.

Jake





[Modified by JAKE, 10:30 AM 4/29/2004]

 

I just went out and checked and the car is pulling 13in at 900 or 14-15 with the HVAC/Cruise vac line off. We let it idle for quite awhile to get it to drop down and it never popped. I put a hand vac pump on the AFPR and it doesn't hold vacuum very well - the stock one on my 90 doesn't hold either but it leaks about a third as fast.

As far as the type of cam - I have no idea. The only info I have says it is a LPE JL2 cam. It may still be that or not - I dunno.

I really do not want to do another compression test because the entire exhaust system/headers/starter/cluctch slave must be taken off. The miss is not nearly as bad as it was with the broken spring.

Could the miss have been from fouled plugs? They did look pretty carboned up from running rich with MAF messed up.

 

I didn't know your plugs had fouled out; a fresh set of plugs is the order of the day.

Jake

 

The car runs again! Or at least as well as it did when we bought it.

We put a can of GM Top Engine Cleaner in the tank (1/4 full) and ran it for a few miles and the miss cleared up.

I'll probably post a new topic later trying to fix the rest of the problems but I need to get more data first.

Thanks for the help everybody! If it wasn't for the Forum - this car would never leave the garage.

Dale