Spark plug wire question. (Fixed it!)

[langester]

I have been trying to get my engine running for the last 3 weekends. I have done just about everything I can think of. Everything is new, distributor, plugs wires, rebuilt carb, etc. Not a complete rebuild, it is a low mile 89 5.0 H.O. that I converted to carb, used the same cam and just cleaned up the heads and installed new valve seals. I did install new rings, bearings, oil pump and timing set.
So today I decided to check my plug wires, they are Carquest premium 8mm wires, I am running an HEI (gm) style distributor.
I checked the wires with my ohm meter set at 20k range, here are the numbers I got.
1- .98
3- 3.94
7- 1.4
2- .78
6- 4.89
5- .96
4- 1.41
8- 1.09
Wires 1 and 5 are the shortest and 4 and 8 are the longest. I think the 3 and 6 wires are what is causing my problems by seeing the numbers but I am no expert on the subject.
I am hoping someone here can shed some light on the subject for me.

As always Thanks in advance!

 

[gr8scott]

So, converting to ohms:
1- 980 ohms
3- 3940 ohms
7- 1400 ohms
2- 780 ohms
6- 4890 ohms
5- 960 ohms
4- 1410 ohms
8- 1090 ohms

Not the best wires, but the engine should still run. Have you tried verifying spark?

 

[langester]

Thanks for the reply. The engine runs, at high rpms it runs great, on the low end at idle it starts to spit back through the carb intermittent and then dies. It will start right up but then repeats the spitting after a short period. If I raise the idle fairly high (1000rpm or so, I don't have a working tach) it doesn't happen. I have checked the timing multiple times, I swapped carbs and even rebuilt the second carb again. I have replaced the coil, module and distributor cap, and spark plugs. All new fuel line, new filter and fuel pressure regulator. I have tried setting the timing from 0 - 20 Btdc and nothing seems to help. When I saw the difference in the wire readings I was hoping it might be them. I will get another set and give that a shot.
I have never had an engine act like this, I am kinda stumped at this point.

Edit: I forgot to add, I am running a GM style HEI distributor, Motorcraft plugs gapped at .050, and Edelbrock 1405 carb.

 

[oldiron]

All classic symptoms of a vacuum leak. Backfiring/popping thru intake and carb have in my experience been either an overly lean condition (vacuum leak) or incorrect timing/firing order. The part where it runs great at WOT is the giveaway for a vacuum leak/lean.
Greg
edit: You are running the HO firing order aren't you?

 

[triracer67]

I purchased a used motor and PO insisted it was HO, and spark plugs wires were placed in HO firing order. It ran, but, had a bad back fire. After much trouble shooting, I checked firing order on rocker arms and discovered it was standard 302. New firing order solved all the problems. It always ran, the difference is firing order in middle plugs...

 

[gr8scott]

edit: You are running the HO firing order aren't you?

He did post his resistance readings 13726548, so he probably is.

An easy way to check firing order is to remove plugs 1, 3 and 5. It helps to have a remote starter. Leave key off, unplug distributor. Plug the #1 spark
plug hole with your thumb. Bump starter until you feel pressure from #1 cylinder. The next one with pressure will either be #3 (HO firing order) or
#5 (302 firing order). If your firing order is correct, then I'm with oldiron, vacuum leak.

Also, those Carquest premium wires aren't very premium. I run Taylor ThunderVolt 8.2mm Spark Plug Wires (rated at 40 ohms/ft)
and I just measured a 42" wire at 133 ohms, which is much lower than your shortest wire.

 

[oldiron]

Good catch gr8! I completely missed that. ;D
Greg

 

[DirtDonk]

Reduce your plug gap langester. While GM used gaps up to .055 and even .060 from what I've heard, our Fords don't like that gap even with a GM ignition.
Now, normally that would have more effect under load and at higher rpm's, but each engine and tune is different and might change that dynamic.

I would reduce it to at least .045" and start there. Maybe even go overboard and back to .042" perhaps, but that's probably not necessary as there are lots of Ford owners running HEI with .045 and no issues that I recall.

And yes, lengths aside, those wires seem VERY inconsistent in their readings. Find out what their ohm rating per-foot is if you can, and verify they're within spec. Then if not, go back and talk to the seller.

Paul

 

[langester]

Thanks for all the replies. I am running the H.O. firing order. When I got the engine it still had the fuel injection on it and was a tag that said 5.0 H.O. so I assumed thats what it was, it is a roller cam. I tried the other firing order and it wouldn't turn over at all.
I had my Buddy come by this evening and we tried another set of wires I had laying around, it didn't change a thing (they were old so they might be bad as well). I have tried to look for a vacuum leak several times, sprayed and sprayed and nothing seems to change the idle. I checked around the carb and all around the intake.
We fired it up and started pulling plug wires, there were 3 that didn't seem to make a difference wire on or off. I am going to try another set of new wires and see what happens. My Buddy seems to think it might be the cam going bad, which would not surprise me since I cheaped out and didn't put a new one in. My bad for sure.
I have no idea what cam is in the engine, whatever was stock for either a Crown Vic or a Mustang. The guy I got it from couldn't remember what car he got it from.
If anyone has any other ideas I am open to anything at this point.
I appreciate all the help!

 

[langester]

I will also try the pressure check on 3 and 5 to verify I have the correct order. I never thought to check it that way. Thanks for the heads up on that gr8scott!

 

[ared77]

"I tried the other firing order and it wouldn't turn over at all."

That seems odd.?:?

 

[langester]

Everything about this is odd to me. I will double check everything again, I am famous for screwing stuff up here lately. Hopefully Friday I can get a chance to check everything out. I will post up when I get it going or burn it to the ground! Ha!

 

[Pa PITT]

Sounds to me like you've got my luck.
I was going to say put in a couple of new Spark Plugs on those bad hole..& iF YOUR Sure I'm wrong on that then just swap hole with some good hole & the bad holes.
See if your issues move to different holes .

 

[langester]

Pa PITT, thanks for the reply! I will try that as well. I had Autolites in it at first, I put a set of motorcrafts in for the second try, you never know with todays parts thats for sure.

 

[Rustytruck]

A cam going away should show on a vacuum gauge or a compression test. bad ignition problems will show on a vacuum gauge too.

 

[langester]

Thanks for the reply!
I am going to do a compression test Friday, I need to rent a tester. I have had a vacuum gauge attached the entire time, max I can get is 13.5, I am at about 6500ft elevation. Stock cam in the engine, not sure what the cam is. It runs but seems to have a miss, vacuum stays steady until it starts coughing up through the carb at idle then dies out. What should I be looking for on the vacuum gauge to tell for sure?

 

[oldiron]

Around 20 for a stock cam. You have a mechanical issue somewhere orrrrr, wait for it.....a large vacuum leak. Smoke test would narrow it down.
Greg

 

[Rustytruck]

A steady vacuum needle if there is a miss the needle will pulse with the miss. a twitchy needle is usually a fuel mix issue. a cam or valve issue will show as a large drop and jump up of the needle. look up reading a vacuum gauge any time spent there to understand a vacuum gauge is really worth the effort. one of the cheapest diagnostic tools out there but the one tool that tells you the most information on the health of your engine. a high steady reading is a healthy engine. the more the needle the worst shape the engine is.

 

[B RON CO]

Hi, if you did all the ignition work and still have the problem you should be aware that when guys use an aftermarket aluminum intake manifold that it is somewhat common to have a vacuum leak at an intake runner, sucking oil out of the valley. I know Edelbrock has a very thick gasket set for the intake manifolds. You cannot find this kind of leak by spraying carb cleaner because the leak is under the intake manifold. Many guys will use threaded rods to help guide the intake home to help prevent the gaskets from shifting. I hope this is not your problem, but it is something to think about. Good luck

 

[langester]

Vacuum holds steady until the carb starts getting the backfire. If I bump the idle up the vacuum holds and it does not backfire through the carb.
I didn't think about an internal leak at the intake. I did use studs in the heads to keep the gaskets from slipping. That doesn't mean it didn't happen for sure. I will check out the other tests and see what happens, worst case i will pull the intake and see what I find.
Thanks for the replies, I appreciate all the help. This thing is driving me crazy!