Spark only when grounded to frame

[williamsoa]

I don't know if this has happened to anyone, but I can't figure out how to correct the problem. For a few months now I could not get my car to start, I changed/replaced just about every thing that deals with the ignition. Today, I found the problem; I only see spark when I ground the spark plug to the frame. I found this out when I placed a timing light on the #1 plug and it did not indicate RPMs. When I grounded the spark plug to any where on the frame it produced a strong spark and the timing light registered RPMs. I am thinking I am missing a ground but all my grounds are where they need to be. I can ground the spark plug any where on the engine and it produces a spark and timing light registers RPM. . . except when it is in the engine. Can anyone help?

 

[jeremy1375]

I just want to clarify something. Your title says "Spark only when grounded to frame" - In which case you should clean or replace the engine grounding straps.

At the end of your post it says you get spark when it's touching the engine. Did you mean frame? If you did mean engine - did you check or replace the plug wire? Maybe there's a break in it. Also, did you check the other wires with the timing light?

 

[My1GLaser]

Stock coils in the stock location?

 

[williamsoa]

I apologize for the confusion; yes, the plugs will spark when I touch the frame, intake manifold or valve cover. The wires are good, I checked them with a multimeter; I have another set of wires and it is the same thing. I did check all the other wires with the light and it is the same result.

I have stock ignition; stock coils and PTU in the stock location.

 

[WOTDSM]

Check your grounding wires.

I'm betting you're having a ground issue.

Your coil pack could also be shot.

 

[SmoochDarling]

Well all that mean is either you have a poor engine -> frame ground strap, or your spark plugs are not making good enough contact with head to make ground. So check your ground locations and get new plugs too.

 

[jeremy1375]

I am wondering if the plugs are all fouled out as that would explain the problem. When the plugs are sparking outside of the engine, are you using a spare plug and leaving the plug in the engine?

If you are pulling the plug, is it wet or coated with black carbon?

 

[williamsoa]

Ok where to start; I used an external plug to check spark and I have taken the plug out of the engine and checked for spark...they both have spark. Next ground strap...I thought about that too; since I did relocate my battery to the back I cleaned the paint away from the rear shock tower to ground the battery. I have two coil packs so I swapped both of them and still have the same problem. The question about the fouled plugs; #2 plug was fouled and the others were wet with fuel as if they were not firing. I cleaned all plugs and the same thing happened; that is when I started testing with the timing light. I have had these a pack of NGKs for several years but only use the extra ones to test my car for spark. I do think it is ground....I checked them for voltage drop but nothing out of the ordinary.

I am going to run the battery cable to the front of the car and ground the cables going to the transmission and the starter to that; hopfully that will work.

 

[williamsoa]

SmoochDarling, I think you are right. For some reason, my spark plugs were bad. . . all 8 of them. They didn't have any visible damage so I do not know what was wrong with them. I did have one new plug though; I replaced it and cranked the car, sure enough, it registered RPMs on the timing light. Who would have thought $2.50 part would cause so much problems. I will check the rest of the wires with the same plug to see if everything checks out. Thanks everyone; I have plugs on order, as soon as I get them in I will let everyone know the good news. . . . I hope.

 

[williamsoa]

This is the result of the problem with my spark plugs. For some reason, internally the electrode is grounded to the body of the plug. I do not know how this is happening; it took me a while to figure this out because I thought (as you can see by my previous posts) it was my ignition system. I only found this out after replacing numerous ground wires and decided to test ground to the plugs. I noticed that the plugs would read 3 mega ohms . . . how can this be when it is supposed to be insulated. 2 of the 4 plugs had this reading, the others where of couse an open circuit.

Does anyone know a reason why this would happen; excluding dropping or crushing the plug. There is no external damage to the plugs.

 

[luv2rallye]

If the plug's insulator had a hairline crack (possibly on the inside where you cannot see) it would do that.

 

[williamsoa]

I guess I got a bad batch of plugs. Definitely takes trouble shooting to a whole other level.

 

[williamsoa]

It ended up being the ground cable from the transmission to the chassis. I checked the resistance on the cable and it was reading 2 ohms. I cut the cable out of the harness and stripped the insulation off and found that the copper wire had that green patina through the lenght of the cable. I bought a new length of 4AWG wire and soldered eyelet connectors to both ends. Now the car starts first time every time. That confirms I will have to re-wire the entire car this season.

 

[TSiAWD666]

Ugh, nice find and good update. I've had corrosion like this occur in two cars in the past two weeks preventing starting. Looking for corrosion in wiring is often the last thing people think of because usually the car was working just fine and all of a sudden it stops and so you think it's some catastrophic part failure rather than a gradual one (like corrosion). Everyone should inspect their wiring once in a while on these old cars!

 

[williamsoa]

Amen brother! This experience was painful but, I know how to troubleshoot every electrical part in the car now. As soon as I start the rewiring process, I will post that as well. I plan on keeping the wiring that is interior to the car unchanged but using a painless system for all my aftermarket electronics (a/c, gauges, controllers, etc.) and building an engine harness from scratch.