ultimatefighter

Hi all. I am having problems with my 1992 Z, 305TPI. If the bypass wire is plugged in the car won't start, if it does, it spits and sputters then dies within seconds. Now, with the bypass unplugged, the thing fires right up. What could cause this?
Also...the engine runs smooth all the way up to 2500 RPM, anything above that, it spits and sputters and shakes and knocks. All sorts of weird sounds. Basically, under a load it has no power and misses and pops, etc...anybody have any ideas?
Thanks

jermdm

Sounds like a bad ignition module or esc module. If it runs ok with the wire disconnected, check your timing to see if its spec. Check for engine codes. Just got to start checking things out.

ultimatefighter

It has a brand new ignition module. It doesn't run OK with the wire unplugged, but is driveable. It still has the same symptoms, but WILL start with it unplugged. I have also checked the timing 100X and it is dead on 6* BTDC. Also, the thing that is puzzling me>>>>and frustrating, I put the code reader on it and I only get a code 12. That is why I am lost. I can drive the thing to the store, like it is in limp mode. But, as soon as you give it anymore gas, it spits and sputters and misses.
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BTW.....New plugs, cap, rotor, coil, and ignition module.

ultimatefighter

If it is the esc module, would I need a new computer?
Thanks!

JP86SS

iTrader: (1)

If you get code 12 (No distributor Reference Pulses) with the engine running the problem is the pickup coil in the distributor.

ultimatefighter

I didn't know you were supposed to check the codes with the engine running. Manual says to check with ignition on, not running. Which then a code 12 means the diagnostics are working? Should I check the codes while the engine is running with the code reader?
Thanks for the replies.

ultimatefighter

Can I check the codes off a plug in reader when the car is running, and get different results??????
Please help. It will soon be too cold to ride my motorcycle.

titchener

Ultimate-

I just had a similar problem with my '91 Caprice. After a few web searches I turned up some claims that running ok with the EST wire off and running poorly with it on is the sign of a weak signal from the distributor, meaning likely a bad pickup coil, cracked magnet, worn distributor bushing or other internal distributor problem.

I yanked mine out and it was a rebuilt unit (strike one). On this one it had a ton of shaft endplay, almost 1/8". When running the engine pushes the shaft up, on this unit that meant the center pole pieces were only partially (about 2/3's) overlapped with the outer magnet ring.

That alone can make the signal weaker, and this unit also had an aftermarket low buck looking sensor coil. I replaced the sensor coil with an AC one and added shim washers to bring the endplay down to around 0.015", which makes the pole pieces line up correctly with the magnet.

This fixed my problem, could have been either the pole piece misalignment or a bad sensor coil. The coil measured ok, around 800 ohms and infinite from either terminal to the distributor body, but apparently the coils can still act up when hot even if they measure ok. You can measure the sensor coil with the distributor in the car, just disconnect it from the back of the spark module.

Even if the coil measures ok, I'd still pop your distributor out and take a look for problems with it. Sometimes you'll see enough corrosion to cause problems with either the magnet system or the sensor coil.

www.gmpartsdirect.com has the best prices I've found on real GM parts for these distributors. The sensor coil is only around $13., if you have any doubts about it I'd replace it. Also check for too much slop in the upper distributor bearing, there should hardly be any play at all, too much and it can cause contact of the inner magnet and outer pole pieces, if you see any of that the bushing is definitely shot.

Good luck, and post back how it works out-

Paul T.

ultimatefighter

Man, I soooo much appreciate all that info T. Thanks alot. Will replace the pick up coil and check shaft end play tomorrow. Might just pick up a new dizzy.....don't know yet. Thanks again and I'll report back.

titchener

A little more on shaft endplay- the factory spec is apparently 0.015" to 0.090", which is pretty loose (mine was even over that at around .125").

But for best performance you want it to be on the small end, around 0.015". If it gets up around 0.090" or more, as in my case the magnet pole pieces stop lining up well and your signal gets weak.

Also some claim that too much endplay leads to variation in the timing, since as the shaft moves up and down the rotor moves back and forth, but I'm not sure that really happens, I think when the engine is running the shaft is always pushed up against the thrust washer.

Unfortunately its hard to find distributor shims for these units, they have a skinnier shaft than the older chevy ones, its around .427" compared to around .500" for the earlier chevy ones, and most the of the shim sets you find will be for a .500" shaft. I don't like using the bigger shims as they'll flop around on the shaft too much.

Chevy used to sell a shim set in the smaller size but the last time I tried to order it they said they weren't available any more, but if anybody has a supplier or a live part number for these smaller shims, please fill us in.

Paul T.

ultimatefighter

Thanks alot for the input. You were right on with the coil pick-up. Fixed it, and now she's barking again. Revs right up with no miss. Funny thing is, now my tach is acting funny. Checked all the wires,but.....just happy to be back on the road.

Thanks alot for all the replies!!!

ultimatefighter

Well, it ran execellent for a couple runs. Now its doing the same thing accept in a lower RPM range. When I kick it in, it runs out smooth. So, I unhooked the EST wire and it runs fine that way. Now what??? It just does it at cruising speeds! Idles perfect. Start perfect.

titchener

Is the tach still acting funny? If so that could be a sign that something else is still wrong.

Except for reduced power, does it run without missing with the EST wire disconnected?

If so that's still likely a sign that something is wrong in the ignition system.

Are you sure your timing is set correctly? When the EST wire is unhooked the timing is retarded a lot, so if its set too high this makes the car run better.

Was there a lot of corrosion in your distributor when you changed the pickup coil?

Also when you replaced the spark module was their corrosion on the pins? If so the connector part could still have a lot corrosion on it causing a bad contact, if you're not sure pull it off and look closely inside it with a flash light.

RBob

iTrader: (1)

You could be fighting more then one problem. Have the injectors been replaced? By now about every 3rd gen with Multec's have to be bad.

RBob.

ultimatefighter

Funny thing is, the tach jumping went away. I rechecked the timing after tightening the dizzy all the way and it is dead on 6* BTDC. I took it out for a little spin and it smoked the tires and barked in 2nd. Then, the next day it goes back to almost the same symptoms. And yes, it does run without the EST wire hooked up, just lack of power, but no misses. All the way through the powerband. There wasn't alot of corrosion when I changed the pick-up coil. I will look closer at the pins though. The bad thing is, I have already thrown alot of money (to me any ways) at this thing and can't afford a fuel pressure gauge to check the fuel at the rails. $40 for something I will probably never use again. That's just me, I'm poor! LOL. Is there a way to check the injectors without expensive of fancy equipment? Thanks alot!
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BTW....if this helps. This whole time before the pick-up coil, the check engine light was constantly on. Then it went away until I unplugged the bypass wire on the way home from the store to see how it would run. I know that's why it came back on. Might help, might not.

ATX-Iroc

try switching the wires that go to to the module around. if you got them mixed up the est would be retarding your timing instead of advancing.