Author Topic: Diagnosing a "miss" - fuel or electrical? (Read 6132 times)

_Russ_ · « **on:** October 13, 2012 - 07:52:51 PM »

So my Challenger has been giving me some trouble lately, even needing a tow home a few weeks ago.

Here is what happened on the day it was towed home: (excuse if this becomes a little long winded)

Driving to work in the morning, everything is fine. Starts fine, cruises through suburbia @ 40mph fine. Then I hit the Freeway. Sitting on about 65mph everything seems OK until I come to the first hill. Give it a bootfull to get up, and it "misses" a couple times. There is no backfiring, no popping from the carb. Just a few of what a l like to call "kangaroo hops". I back off the throttle, get it up the hill and it seems to be OK again. Does it again up the next hill - but that's it. Never again on the way to work.

On the way home, same thing, except this time backing off doesn't help. First steep/long incline and it starts again. I try to back off, but this only lasts 5 seconds and it starts again. I pretty much kangaroo hop the entire hill at 50mph (must have looked hilarious to other commuters!). Does it sporadically for the next few miles, then the engine quits.

Fortunately it happened at a decent spot on the Freeway with little traffic, so I was able to get it off to the side and out of the way without causing an accident. Sat there for about an hour waiting for the Tow Truck - and in that time it wouldn't run again. I did a quick check over everything under the hood - every lead/connection - electrical & fuel. It would crank, but die immediately.

Got it home, left it over night. Next morning I went out and it fired up first time - without a problem - but decided not to drive it until I figured it out.

Thought it may have been an ignition problem. Heard/read a lot about the same problem others had with the culprit being a failing ignition coil. I swapped out the coil yesterday and took it for a spin - same result. Fine around town. Hit the Freeway - and the first hill I came to? Kangaroo time! Managed to get it home unassisted though - always a bonus.

The reason I initially suspected the ignition was that about 2 months prior a mechanic had serviced it - filters, plugs, leads and given it a tune up - but I always felt it didn't run quite right after that. Can't explain it but it felt different. Not sure if it's pertinent, but after the tune up, talking about the timing the mechanic stated he removed "about an inch of advance".

Here's a basic rundown:

- Fine around town at 40mph.
- Initially fine on flat Freeway @ 65pmh (approx 2700 rpms)
- Starts missing on inclines under acceleration around 70mph (3000-4000 rpm range)
- Always happens under load. Never happens during idle in Neutral/park, regardless of revs.
- Replaced both Ignition coil and Orange Box on firewall - no change.
- Air filter is covered in fuel (only just noticed this). It's filthy. Should have been cleaned last service.

Car specs:

Engine: 383 Magnum
Trans: A727 TF
Carby: Holley 650 Double Pumper
Ignition: (Electronic) Mallory Coil. Mallory Unilite Dizzy (Mechanical advance).

Any clues as too what I should be looking at?

I'd really like to try and figure this out on my own before taking it to a pro, and would appreciate any & all help.

Thanks for your time,
Russ

dodj · « **Reply #1 on:** October 13, 2012 - 08:20:51 PM »

Too much advance?
Check your total advance at 3000 rpm. About 36*?

PlumCraZRT · « **Reply #2 on:** October 13, 2012 - 10:54:06 PM »

Quote from: dodj on October 13, 2012 - 08:20:51 PM

Too much advance?
Check your total advance at 3000 rpm. About 36*?

That would be my thought as well. Leave the vacuum advance disconnected.

Did he play with your power valve or jetting?

tman · « **Reply #3 on:** October 13, 2012 - 11:37:41 PM »

Im kinda thinkn fuel level in the bowls. Its occuring on incline where the fuel level is going to either the back or front of the fuel bowl. Level too high or low........ If you are not having problems during load on level, then it sounds like fuel delivery. Just a possibility.

PlumCraZRT · « **Reply #4 on:** October 14, 2012 - 02:37:02 AM »

Quote from: tman on October 13, 2012 - 11:37:41 PM

Im kinda thinkn fuel level in the bowls. Its occuring on incline where the fuel level is going to either the back or front of the fuel bowl. Level too high or low........ If you are not having problems during load on level, then it sounds like fuel delivery. Just a possibility.

That's a good thought.

I was assuming it's something with timing and the vacuum advance, since you would see extra load on an incline.

tman · « **Reply #5 on:** October 14, 2012 - 03:00:32 AM »

You also mention air filter covered in fuel. You mean dirty with something or was it soaked with fuel. Needle valve may be defective allowing fuel to go places it doesn't belong. Another possibility. See where your fuel bowl level is after running the car for a bit.

_Russ_ · « **Reply #6 on:** October 14, 2012 - 05:14:00 AM »

Quote from: tman on October 14, 2012 - 03:00:32 AM

You also mention air filter covered in fuel. You mean dirty with something or was it soaked with fuel. Needle valve may be defective allowing fuel to go places it doesn't belong. Another possibility. See where your fuel bowl level is after running the car for a bit.

Soaked in fuel. It was pretty much everywhere. The base of the air cleaner was lined in it. Would have been a good tablespoon full on there.

Put a paper towel on the top and it soaked it up around the top ring of the filter.

GranCuda1970 · « **Reply #7 on:** October 14, 2012 - 08:28:16 AM »

I agree with dodj timing issue!

Chryco Psycho · « **Reply #8 on:** October 14, 2012 - 11:25:59 AM »

have you done a compression test ?
I wonder if you are getting pressure back through the carb with a bad intake valve pushing fuel up into the air cleaner . I would say it has more to do with load , when the engine has to work harder it starts to backfire , could be ign related as well .

BS CUDA · « **Reply #9 on:** October 14, 2012 - 11:32:18 AM »

I had a similar issue. I was running an Edelbrock HP mechanical fuel pump and removed the regulator to clean up under the hood as Edelbrock stated the regulator is not required. I to questioned electrical or fuel. I too would end up with sputtering at cruise / under load as well as lower speeds on hot days and engine dying with fuel sitting in the air cleaner base. Mine would eventually start again with throttle down and I made it home by keeping the RPM way up in a lower gear thus seemingly useing the fuel. I figured mine out finally by warming the car up fully and then in the garage revving it up and holding the secondaries wide open and it eventually it would start puking fuel out the breather tubes as the pressure was too great for the needle and seat to hold the fuel back. Just an idea from experience but sounds like a similar issue. Once I reinstalled a proper regulator - No more issues. I have since installed an electric pump and bypass regualtor to eliminate boiling fuel as well on very hot days.

tman · « **Reply #10 on:** October 14, 2012 - 03:58:37 PM »

All suggestions from everyone are good. But BS explanation is getting more to what I was referring to. A little dirt on the needle and seat could be the problem. If you have been running the same setup for a while (fuel pump/carb) with no problems and now you are having this problem, could be fuel delivery. Checking timing is easy since the mechanic messed with it. Put the timing back to where it was before the mechanic. Not that hard to do a tune up with electronic ignition. So when you mention he did "leads" not sure what that is. Is that ignition wires? "inch of advance" what does that mean in "degrees?" Sounds like a lot.

Chryco Psycho · « **Reply #11 on:** October 14, 2012 - 04:04:29 PM »

Check the gap in the dist too electronic needs a .008 gap between rotor & pick up , make syre the rotor & cap are in good condition , ign wires could be bad too you can check them with an Ohm meter , should have 7-20k ohms resistance .

_Russ_ · « **Reply #12 on:** October 14, 2012 - 10:25:09 PM »

Quote from: tman on October 14, 2012 - 03:58:37 PM

All suggestions from everyone are good. But BS explanation is getting more to what I was referring to. A little dirt on the needle and seat could be the problem. If you have been running the same setup for a while (fuel pump/carb) with no problems and now you are having this problem, could be fuel delivery. Checking timing is easy since the mechanic messed with it. Put the timing back to where it was before the mechanic. Not that hard to do a tune up with electronic ignition. So when you mention he did "leads" not sure what that is. Is that ignition wires? "inch of advance" what does that mean in "degrees?" Sounds like a lot.

Yeah sorry mate. ignition "leads" are spark plug wires.

I have no idea what he meant by "inch of advance". Have been trying to figure it out ever since he said it. The only thing I can thing of is, like you say, he was referring to the distance change between the degree marks on the pulley - which would be a rather significant amount. If that's what he was referring to, it would be close to a 10� change.

Idle timing is set at 12�. Unsure of advance & total timing. Little awkward checking it on my own.

I have been running the same set-up since I bought the car 2 years ago. Over 20,000 miles in those 2 years, including 3 interstate road-trips - and this is the first problem it has ever given me. It never felt right after they messed with it. Might be a simple coincidence. Might not.

Before I start playing around with the carby I'm waiting on a couple Holley rebuild/tuning books to arrive. It's a part of the car I have no real hands-on experience with

Just want to be sure I don't bugger things up.

Thanks to everyone for their input. Anything else comes to mind, please keep it coming.

I'll update as things advance.

_Russ_ · « **Reply #13 on:** November 13, 2012 - 03:13:33 AM »

Bit of an update on this.

Had the Challenger Dyno-tuned. The advance was way off. I won't use the exact words the mechanics used regarding the previous mechanic's "effort" at timing it, as I'd probably get banned - suffice to say it's in my best interest to never give them my business again! haha

Anyways. What was discovered:

- Fuel filter was blocked. Couldn't even blow through it. Reason being ...

- The fuel inside the filter and what immediately poured out the lines was filthy. Looked like chocolate milk - and that's not one bit of exaggeration. It was putrid. For consistency, I only ever use fuel from 1 company, and always BP Premium 98 Octane. No crappy Ethonol based junk goes near my car. My guessing is the tank has crap in the bottom from over the years, and was disturbed and loosened a couple months back when it was removed whilst replacing the trunk floor. Shame I didn't have the common sense & foresight to inspect it and get it cleaned then.

- Voltage drops. There is a a 1 volt drop from the fusible link attached to the inner fender. There is an almost 2 volt drop from the firewall side of the fuse-panel (not sure which wire exactly. Need to get it pin-pointed). So that's about a 3 voltage drop in total.

- Spark Plug Wires / Leads suck. These were bought and installed by the previous "mechanic". I never liked the feel of them (felt cheap and plasticy). New guy says they're not good enough, won't be able to handle the load, and will give way sooner rather than later.

- Valves were too tight - He said they were too tight and readjusted them.

So where did that leave me? As I said in my initial post, the morning after it quit on me, it started right up without hesitation - this made it hard to pinpoint the problem.

After the dyno-tune? Ran like a dream for 2 days.

The initial stutter/miss was gone. The thing drove beautifully. All RPM's, all gears, all speeds up to 90MPH. Didn't miss a beat. Uphill; downhill; idling; cruising; fangin' - never ran better. Literally. Hadn't ran & sounded that good in the 2+ years I've owned it. I was a happy dude.

Then Sunday morning came. Went on a cruise for a couple hours. Did about 300km, then 2km from home and ... nothing. Driving up the street and the engine quit. No stuttering/hopping/missing. Just driving along and .. nothing. Radio was fine. Wasn't an entire electrical shutdown. Just the engine. Stopped cold.

Sat for half an hour waiting for the towie to arrive. Same as the first time - would crank, but not fire-up. Got it home, tried for a few hours - same thing. Next morning? Fired right right up. No problem.

This is all it could do the day it quit:


www.youtube.com/watch?v=PvOJEhLS5NQ

My summation is the initial problem I had was two-fold. 1 was the timing/advance causing the stuttering/hopping/missing on the freeway. This was fixed with the dyno-tune.. The 2nd problem - the engine quitting - is something else. First thing I'll be doing is cleaning the fuel tank; changing the spark plug wires; replacing the fusible link wire; pinpointing the firewall/fuse-panel voltage drop.

Any thoughts?

PlumCraZRT · « **Reply #14 on:** November 14, 2012 - 01:44:30 PM »

Quote from: _Russ_ on November 13, 2012 - 03:13:33 AM

My summation is the initial problem I had was two-fold. 1 was the timing/advance causing the stuttering/hopping/missing on the freeway. This was fixed with the dyno-tune.. The 2nd problem - the engine quitting - is something else. First thing I'll be doing is cleaning the fuel tank; changing the spark plug wires; replacing the fusible link wire; pinpointing the firewall/fuse-panel voltage drop.

Any thoughts?

I would check the fuel bowl to see if fuel is getting there. My guess would be the filter is clogged again. Get a new tank (instead of cleaning the current one) and new filter. Replace the wiring, etc as time permits.

Author Topic: Diagnosing a "miss" - fuel or electrical? (Read 6132 times)

_Russ_

Diagnosing a "miss" - fuel or electrical?

dodj

Re: Diagnosing a "miss" - fuel or electrical?

PlumCraZRT

Re: Diagnosing a "miss" - fuel or electrical?

tman

Re: Diagnosing a "miss" - fuel or electrical?

PlumCraZRT

Re: Diagnosing a "miss" - fuel or electrical?

tman

Re: Diagnosing a "miss" - fuel or electrical?

_Russ_

Re: Diagnosing a "miss" - fuel or electrical?

GranCuda1970

Re: Diagnosing a "miss" - fuel or electrical?

Chryco Psycho

Re: Diagnosing a "miss" - fuel or electrical?

BS CUDA

Re: Diagnosing a "miss" - fuel or electrical?

tman

Re: Diagnosing a "miss" - fuel or electrical?

Chryco Psycho

Re: Diagnosing a "miss" - fuel or electrical?

_Russ_

Re: Diagnosing a "miss" - fuel or electrical?

_Russ_

Re: Diagnosing a "miss" - fuel or electrical?

PlumCraZRT

Re: Diagnosing a "miss" - fuel or electrical?