NEED HELP! 1986 720 Battery Shorted Out Against the Hood. Now Has Bad Engine Miss.....

[Yinzer]

Just did a Compression Test. The results are as follows:

 

Cylinder #.............(1).........(2).......(3)........(4).

Exhaust Side........185........185......180.......185.

Intake Side...........180........180........70........85.

 

Exhaust Side has AC Delco 41-629

Intake Side has  NGK BPR6ES

 

 Plug readings didn't look horrible front two bit black with carbon. Back two tannish.

 

 Blown head gasket ???

 

 What say you ?

[datzenmike]

Each cylinder has two spark plugs so you only need to do one of the plugs.

 

I see cylinder 3 and 4 on the intake side were extremely low. (which is impossible) Probably because they are hard to get at. Go with the exhaust side numbers. Average is 183.75 which is near perfect.

 

The head gasket would not blow just because the battery shorted to the hood.

 

 

 

 

Can you access this idle mixture screw???

 

 

I assumed this screw would be sealed off like the factory ones are. If the screw is accessible turn it in gently till it bottoms out, counting the turns so it can be put back in the same position. Sorry for this, but remove the idle cut solenoid and with the mixture screw out, spray into the idle cut hole.... expect spray to fly out the idle mix hole. Now spray the idle mix hole and hopefully it sprays out the idle cut hole. Now bottom out the idle mix screw and turn out the number of turns you recorded earlier.

 

 

See if that helped.

 

 

Also your vacuum advance is not connected to the carburetor base. Makes me wonder where it is connected.

[Yinzer]

27 minutes ago, datzenmike said:

Each cylinder has two spark plugs so you only need to do one of the plugs.

 

I see cylinder 3 and 4 on the intake side were extremely low. (which is impossible) Probably because they are hard to get at. Go with the exhaust side numbers. Average is 183.75 which is near perfect.

 

The head gasket would not blow just because the battery shorted to the hood.

 

Can you access this idle mixture screw???

 

I assumed this screw would be sealed off like the factory ones are. If the screw is accessible turn it in gently till it bottoms out, counting the turns so it can be put back in the same position. Sorry for this, but remove the idle cut solenoid and with the mixture screw out, spray into the idle cut hole.... expect spray to fly out the idle mix hole. Now spray the idle mix hole and hopefully it sprays out the idle cut hole. Now bottom out the idle mix screw and turn out the number of turns you recorded earlier.

 

 

See if that helped.

 

 

Also your vacuum advance is not connected to the carburetor base. Makes me wonder where it is connected.

 I'll check all out tomorrow after work.

 

 Would a backfire blowout a head gasket perhaps ??

 

 Average 183.75 PSI in a truck with 195,xxx seems unusual. Makes me think the engine was replaced not long ago. The block is blue. Is that OEM perhaps ?

 

[Yinzer]

Just took a quick look. I can access that mixture screw. I'll clean out that circuit tomorrow.

 

 Also, I don't see or feel ANY vacuum ports to the distributor's vacuum advance...but I do see a wire attached to it.  Weird....

[datzenmike]

 

Vacuum advance is the plugged port on the right not too far from the mixture screw. Should be hoses and hard lines to the distributor. So some genius pulled all the hoses off thinking he was 'de-smogging' this engine.

[Yinzer]

1 hour ago, datzenmike said:

 

Vacuum advance is the plugged port on the right not too far from the mixture screw. Should be hoses and hard lines to the distributor. So some genius pulled all the hoses off thinking he was 'de-smogging' this engine.

Yea, the PO did all that when he installed the new carb.    

 

 I need to find a pic of a Z24 distributor with that vacuum port. I cant find a port anywhere on this truck.

[datzenmike]

It's round sort of cone shape and mounted on the out side of the distributor. There it is with a hose on it.

 

[Yinzer]

6 hours ago, datzenmike said:

It's round sort of cone shape and mounted on the out side of the distributor. There it is with a hose on it.

 

 

 

 Mine doesn't have that. NO hose or nipple for one. It does have a WIRE attached that runs into a wiring harness and goes to ??. I'll post a pic. I know... ALL vacuum advances I've ever seen look like your pic.

[powderfinger]

2 hours ago, Yinzer said:

Mine doesn't have that. NO hose or nipple for one. It does have a WIRE attached that runs into a wiring harness and goes to ??. I'll post a pic. I know... ALL vacuum advances I've ever seen look like your pic.

This might have been an 86 with the z24i that someone put an aftermarket carb on. I have read you can do that and leave the crank angle sensor and the truck will run fine. I went ahead and replaced mine with a standard distributor and rewired it.

Edited March 13, 2023 by powderfinger

[datzenmike]

Oh lord....

 

Did not know it would run but all the Z24i carburetor sensors are needed by the ECU under the front seat to set the advance.  

[Yinzer]

Ok, couple updates.

 

 The vacuum advance/retard appears to have HAD a nipple. Seems to have been broken off and left a nub in it's place. Why ?? Who knows. Definitely NO vacuum hose attached anywhere. I added RETARD since I've read that these can also be used to RETARD ignition timing while decelerating to help control emissions.  ??

 

 Update on Cylinder #3 and #4 Intake Compression readings. I repeated Compression testing on both. #3 is at 100 psi and #4 is at 60 psi. All other cylinder readings are between 180-185 psi.

 

See Updated Chart Below....

 

Cylinder #.............(1).........(2).......(3)........(4).

Exhaust Side........185........185......180.......185

Intake Side...........180........180......100........60

 

 I'm not able to keep the engine idling below 2500 RPMs to clean out the idle Solenoid and Mixture screw while running.

 

 I also "tried" to do an Engine Block Leak Test. Didn't work. I need to go watch some YouTube videos and repeat that tomorrow.

[datzenmike]

Clean the idle cut solenoid and mixture screw holes with the engine off.

 

12 minutes ago, Yinzer said:

 

 Update on Cylinder #3 and #4 Intake Compression readings. I repeated Compression testing on both. #3 is at 100 psi and #4 is at 60 psi. All other cylinder readings are between 180-185 psi.

 

See Updated Chart Below....

 

Cylinder #.............(1).........(2).......(3)........(4).

Exhaust Side........185........185......180.......185

Intake Side...........180........180......100........60

 

 

 

 

How is it possible to get two different compression readings on the same cylinder????? Each cylinder has two plugs, they would read the same.

 

Clean the idle cut solenoid and mixture screw holes with the engine off. Also try plugging the idle cut hole when spraying onto the idle mixture hole.

[Yinzer]

3 Videos.... Two of distributor and One engine starting and stalling out.

 

26 minutes ago, datzenmike said:

Clean the idle cut solenoid and mixture screw holes with the engine off.

 

 

How is it possible to get two different compression readings on the same cylinder????? Each cylinder has two plugs, they would read the same.

 

Clean the idle cut solenoid and mixture screw holes with the engine off. Also try plugging the idle cut hole when spraying onto the idle mixture hole.

1) Will do.

 

2) Great question. I have no idea.  I did retest the Compression test on BOTH #3 and #4 Intake cylinders today.

 

 I'm still NOT seeing any milky oil on the dipstick. Absolutely NO smoke of any kind out the exhaust pipe.

 

[Yinzer]

How does one post up videos on this site ??  Uploading to YT is very time consuming. I have a couple videos taken of my engine starting, running and stalling out.

 

   

[datzenmike]

Any chance some plug wires were mixed up?

 

What do the plugs look like?

[Yinzer]

12 minutes ago, datzenmike said:

Any chance some plug wires were mixed up?

 

What do the plugs look like?

 No chance the wires are mixed up. The engine started and ran great before the shorting out incident.

 

 The plugs looked a bit carboned up but not excessive IMHO. Probably from missing the past few days. The front ones were more tan. Non were wet with oil or coolant. 

[Yinzer]

What's the possibility the timing chain jumped time ??

[Yinzer]

24 minutes ago, Yinzer said:

What's the possibility the timing chain jumped time ??

 

[datzenmike]

 

 

1 hour ago, Yinzer said:

What's the possibility the timing chain jumped time ??

 

Never heard of it happening. There is a tensioner to keep slack out of the chain.

 

One tooth is 9 degrees of cam and 18 crankshaft degrees. Would it even start? 

 

 

I see after it stalls that it only starts after you pump the gas several times. That's very informative. That tells me that no gas is getting through to the idle circuit.

[Yinzer]

I'll clean out the idle circuit after work today.

 

I also plan to redo the Compression testing as well. If I have the time today.

[datzenmike]

 

Here is a Z series combustion chamber. Intake spark plug to the top and exhaust to the bottom. It's a mystery to me how #3 and #4 can have different compression readings between these two spark plug holes.

 

Perhaps the threads are damaged and the spark plug seals but the compression tester does not? Is it a screw in type tester or the kind with the rubber tip you push against the hole to seal?

[Yinzer]

10 hours ago, datzenmike said:

 

Here is a Z series combustion chamber. Intake spark plug to the top and exhaust to the bottom. It's a mystery to me how #3 and #4 can have different compression readings between these two spark plug holes.

 

Perhaps the threads are damaged and the spark plug seals but the compression tester does not? Is it a screw in type tester or the kind with the rubber tip you push against the hole to seal?

 It's the screw in kind. I'm going to redo the Compression test when I get the time. I'm real curious about this as well.

 

 Found the problem!! I'll post in the next Reply.

[Yinzer]

The truck is FIXED ! For the most part. Turns out it was a HUGE vacuum leak. 

 

 Apparently when it initially backfired (after the Pos battery post hit the underside of the hood) a bolt (PLUG) shot out of a large vacuum hose under the carburetor. Although I re-inspected all the vacuum hoses/plugs, I obviously missed this one. I was very hard to see the end since it was buried a bit.

 

 I flushed out the Idle circuit/solenoid and mixture screw very thoroughly right before I found the unplugged hole.

 

 Anyways, the engine is still dieseling/run on AFTER I turn the key OFF.

 

 I need to go back and do a full tune up to smooth the engine out.

 

 A HUGE THANK YOU to DAZENMIKE for all your help! I'm very grateful. My wife is too since I don't have to tear the engine apart and spend 100s of $$ ! Lol !

 

 Here's a short video of the engine staring and running as it is right now.

 

 

[Stoffregen Motorsports]

Nice

[Thomas Perkins]

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