El Camino Central Forum banner

1 - 17 of 17 Posts

·
Registered
Joined
·
400 Posts
Discussion Starter #1
I was doing a friend a favor and just beginning to tow his 1975 Chevy Caprice with my tow bar. Got the tow bar hooked up and turned the rig around, went up a little hill and waited at the parking lot exit to begin our trip when the motor died. Tried to restart, engine fired a little but would not stay running. Pumped it twice to the floor and she fired a backfire through the air cleaner assembly (first time my EC ever backfired). Tried to start again, felt like it was running but dying when the starter was released. I was forced to call two tow trucks: one for me and a second for my friend with the Caprice.

The EC is now sitting in the driveway and I am readying my plan of diagnosis and attack for tomorrow. My intentions are to do as follows:

1.) Spray a little ether in carb and see if EC runs (and/or backfires);

2.) Use test spark plug and determine whether I have spark and quality of spark;

3.) Disconnect ECM spark control harness from distributor and view timing while starter cranks engine using timing light;

4.) Pull spark plugs and do a compression test

Please let me know your thoughts on whats wrong and what steps you think I should take to diagnose the problem.

PS My assistant was in my 85EC with me at the time it stopped running and he claims he accidentally bumped or tapped the computer (did not tell me this until the car had been towed back home). My understanding is that 85 EC will run (albeit in limp mode) without the computer thus it seems impossible that a bump to the ECM could set off such a chain of events. My 85 EC has 98k miles with the original engine.

PPS I am leaning to the problem being a timing chain but it stopped running at idle and every prior timing chain failure I have had has failed when starting or accelerating.
 

·
Deputy Director Region 18 Participating Member
Joined
·
6,292 Posts
well,sound like it "Jump" timing,look into the timing chain and check the distributor gear,also check the easy stuff like a bent rotor or the distributor cap. not properly fasten down,if you have points,check the point and condenser.make sure the wires are hook up.:dontknow::beer:
 

·
Registered
Joined
·
479 Posts
Like gilby said, check the easy stuff before you tear into more complicated stuff. Check your fluids, make sure your have spark and fuel, and go from there.
 

·
Premium Member
Joined
·
12,123 Posts
You might watch the distributor rotor while some one cranks the engine. If it doesn't turn smoothly, and jerks a bit, the cam sprocket/chain is likely failed. That's assuming the dist. cap & rotor are OK........dist timing will be retarded if the cam chain has slipped a tooth on the sprocket. Don't know if that year still has the plastic teeth on the cam sprocket....

Then again, it may be something we haven't even thought of!:smileyb:
 

·
Registered
Joined
·
400 Posts
Discussion Starter #8
Went out this morning to diagnose and disassemble my 85 EC (which came home Friday on a hook) as required. This morning I find that I also have a drop or two leaking from the weep hold of the water pump and a slow leak from the freeze-out plug adjacent to the left front of the block.

I started analyzing my no start/no run problem described in the first post. I shot some ether in the carb and the engine did not run. Next I used a test spark plug to test for spark and I found that we had beautiful strong spark. When I attempted to time the engine, I found that the timing marks were at 12 o'clock on the timing cover not at the more traditional 2 o'clock position. Making it practically impossible for me to see the timing marks from behind the water pump.

With the water problems, I figured I had to get down to the water pump and freeze plug as a minimum. So we removed all accessories and the radiator, then the water pump, harmonic balancer and timing cover. Timing chain appears to some slack but does not look like its in bad enough shape to skip time. So my plan appears to be as follows: i.) time engine currently; ii.) if engine is significantly out of time then we can assume that we have skipped time; iii.) it appears time to do the compression test.

Let me know where you would go from here.

The timing marks at 12 o'clock really irk me. I would like to change to 2 o'clock pointer (they are available in all the catalogues and on ebay) but I don't see in any reference as to what harmonic balancer to use. I believe my current 305 LG3 balancer is 6.75". Can the timing line be re-scribed at the two o'clock location and then zeroed with the adjustment on the pointer and a dial indicator on no. 1 cylinder. Any instructions on how to rescribe the 305 balancer.

If anyone has gone down this route I would love to hear from them about their experience.
 

·
Registered
Joined
·
591 Posts
since you have the timing cover is off check to see that the timing mark sprockets line up lower mark at 12 upper sprocket a 6 if they line up then i would do a compression check.if they don't line up a compression test is useless.
 

·
Registered
Joined
·
1,708 Posts
I am wondering if the outer ring of the harmonic balancer has move which is why the mark is not in the right place. I would look at a new one and see how it is marked.
 

·
Registered
Joined
·
400 Posts
Discussion Starter #12
I have the EC stripped down to the timing chain (as mentioned above and the chain is worn but the two dots still line-up). Tried to start the EC again today and again the engine is backfiring (the carb even caught on fire for a little while but no dam).

I just completed the compression test and all eight cylinders are in the 190 to 200 psi range. Making me believe what we really have is a bad ignition module. Its just that all the defective/bad ignition modules that I have seen in the past have caused a no spark condition. Has anyone else had a bad computer module that caused backfires.

Please let me know whether you agree with my diagnosis that the problem is a bad ignition module.
 

·
Registered
Joined
·
852 Posts
Did you check the gear on the distributor? sometimes the pin will shear and let it spin on the shaft a little completely messing up your ignition timing. it sounds like this might be your problem since the cam is still timed right and you have good spark, and its backfiring through the carb.
 

·
Registered
Joined
·
716 Posts
Cookpac ck the 2 wire plug on the dist. I believe its the speed sensor I had one on an 87 of mine with a bugered up connector i.e. intermitant connection and it acted about the same way you are describing Jim, God luck
 

·
Registered
Joined
·
1,663 Posts
I've only seen one chevy with the timing marks dead center under the water pump and that was on a California 1979 Camaro and it also requires a special waterpump,so the question I've got to ask is that the original engine?
Are you sure the outer ring on the damper hasn't slipped?On a new damper I like to take a straight edge and a scribe and scribe a mark across the face of the damper from about an inch on the inner out to the edge of the outer ring so that if it slips you can look at the scribed line see if the scribe is in line or misaligned.
 

·
Registered
Joined
·
400 Posts
Discussion Starter #17
goodcruiser

My 85 EC is originally of CA origin. Maybe that explains the 12 o'clock timing marks but I seem to remember seeing the same timing marks here in NJ on NJ origin chevys back in the 1980s. These 12 o'clock timing marks have a receptacle (a little sheet metal holder) attached to the timing mark indicator which is welded to the timing chain cover and is intended for a timing probe (early computer pickup of timing). This timing probe set-up was used from about the late 70s and, to my best memory, until the late 80s. As a result, the probes are no longer available, serviced or otherwise usable. Making it difficult or impossible to time the 12 o'clock timing mark engine with the factory timing marks. As a result, I have purchased a harmonic balancer cover for my 6 3/4" harmonic balancer from Speedway Motors. See http://www.speedwaymotors.com/6-3-4-Inch-Chevy-Harmonic-Balancer-Covers,1797.html

The harmonic balancer cover is keyed to the woodruff key in the crank snout. Thereby preventing any spinning of timing marks. Additionally the harmonic balancer cover is indexed for both the 12 o'clock and 2 o'clock timing positions. Making this conversion of timing marks much simpler. I plan to install the cover as soon as I sort out my backfire issue. The timing cover will require a new pointer to be attached to the timing cover bolts adjacent to the 2 o'clock position.

Finally, my motor is the original motor to the vehicle as proven out by the last 8 (or 9) of the VIN matching the serial number on the block pad behind the alternator. I am leaning toward my backfiring being caused by a bad bad ignition module.
 
1 - 17 of 17 Posts
Top