MGB 70 MGB runs rough - sputters & backfires esp. cold

[RickB]

A while back the hose to the oil pressure sensor blew a leak & oil got all over that side so the distributor and everything over there got pretty much soaked in oil.

I have no idea if this is related to that, but it has started running rough, especially when cold. This started showing as reluctance to start at all when cold. It eventually did start but then sputtered and popped especially if I tried to drive it before warming up a lot.

What I tried:

Pulled plugs, cleaned them. All but #1 appear to show a overly rich mixture while #1 was just about right for plugs that were replaced a little over a year ago.

Removed blue snap together wire connectors the PO attached to lengthen the wires to the coil and the side of the distributor.
Put on a new female connector for the wire on the side of the dist and made a better connection for the coil.

Noticed the top of the coil seems a tad bit loose - is this a problem?

Opened up dist cap & made sure contacts were clean, scraped off a bit of scale from the aluminum contacts inside & shined up the edge of the rotor.

Screwed in the adjusters on the carbs and then opened them up 12 faces each. Tried running, still pretty rough. Opened them up one face at a time on each down to 16 and it was just getting worse, ran them back up to ten and it seemed to smooth out there. Adjusted idle.

After this the car ran & drove good, lots of power & no backfiring. (it was warmed up)

This morning, back to sputtering and popping.
Until it warmed up - then it ran pretty smoothly.

I plan to check the timing next. Any other thoughts?

 

[jlaird]

Think I would replace that coil. Heat makes it get larger and could make the connection inside better.

 

[Mickey Richaud]

How's the dashpot oil? Maybe go with a little lighter weight oil to lessen the damper resistance?

 

[RickB]

How's the dashpot oil? Maybe go with a little lighter weight oil to lessen the damper resistance?

I will give that a try, I had some motor oil handy and put that in - about the same time these troubles started.

Jack - good point, I'll see if I can locate a coil.

 

[RickB]

I replaced the motor oil (20-50) with 3-in-1 oil (I had some in my kit) and it acted better. Not all better, but after a few minutes it straightened out. Might be due to sitting out in sunshine all morning versus nearly freezing night time start up.

I'll see about replacing the 3-in-1 with MMO later today and see what that does for it.

 

[RickB]

I drove it in again this morning, it was sputtering and popping worse than ever.
Here is the strange twist to the story:

I was turning it around in the road to take it back home and it died (right in the middle of the road in the dark on a hill).
When I started it back up it ran perfectly smooth and I drove it in to work and all was fine, until I got to the end of the offramp off the freeway.
Then it started sputtering again.
Noticing the fuel seemed low I pulled into a nearby station and put in a couple gallons. Started back up and it ran smoothly the rest of the way to work!

I find this to be very strange, but I don't understand what's going on.
Ideas? Help?

 

[WA1KWA]

Bad gas?

Colin

 

[RickB]

<div class="ubbcode-block"><div class="ubbcode-header">Quote:]Bad gas?[/QUOTE]

I shouldn't think so, that tank was from Costco gas. I got a few gallons from a different source (Shell) this morning and we will see how it is this afternoon.

Starting it up in the work parking lot was pretty embarrassing yesterday.

When it runs right it idles at 1000 rpm and runs up in 4th gear to 6000+ rpm. Fortunately there were no troopers on the road this morning... :wink:

 

[Jagboy69]

When was the last time you had the gas tank off the car? Either your gauge is lying or you have crud in your tank. I'd pull a fuel sample in a clean glass jar at the carbs. Let it sit for a couple of minutes and look for water. You probably have been over this already, but check your electrical connections at the fuel pump. Do you have another fuel pump you can try by substitution? Might be worth trying, it only takes 5 minutes to swap it out. Something is cutting off fuel, be it blockage, Water, LUCAS, something is causing you to not get fuel momentarily. Hence the sputtering, dying, farting and lying. ;-)

Jason

 

[RickB]

Thanks Jason, when it happens it does kind of feel like it's either momentarily losing spark or fuel.
Weird that it just kicks in and runs right after a while though.
That part really has me puzzled.
I will look at the wiring at the pump.
I have an electric pump (Facet) I could put in temporarily, I'll try that and see what happens.

Didn't mean to say it only took a couple gallons to fill it, the gauge is ok - I just chose to stop at about 3 gallons.

 

[RickB]

I sprayed out the distributor with carb cleaner and it started and ran good for about 10 miles. I got to the top of the hill (where highway 18 intersects with I-90) and then it started up again. Why it waited until it was warmed up this time I can not say. I pulled off to the shoulder and let it run a bit then it seemed better and I was able to drive home.

I'm going out to put the Facet pump on it and see what happens.

 

[Jagboy69]

Rick, we'll nail this issue sooner or later. Look for things that happen at the same time. For instance, "every time the car turns left" or "every time the car is not on level pavement" or when it's reached a certain temperature. This is about the second time I've noticed in your posts you were either turning around, at the top of a hill or coming to a stop I think you said. I have seen ignition coils crap out after getting hot. If it's still the same after you switch the pump, then it's got to be ignition. The next time your out, stop at an autozone and buy a 12dollar coil. I did this once to isolate a problem I was having on the Jag. (I returned it later)

Does anyone think a condenser could cause this? I know when one is going south, the car will run like crap. See Misfires OR
Other ignition stuff here

 

[RickB]

Thanks Jason,
That's why this one is so strange.
Generally it's been after the car has sat for hours and is 'cold'.
It started popping & missing when I first started out from my parking spot.
It got worse as I went, then I either turned it off or it died and then it started up and ran right.

This time it was warmed up, I had been driving uphill, then the road leveled off and the popping & missing started up again. I pulled over and it straightened out and I drove home.

I just ran it with the Facet pump installed and it ran OK for about a 10 mile round trip.

The real test will be tomorrow morning.

 

[dklawson]

Before you invest in a new coil or other new parts, have you checked your float valves yet?

The symptoms you describe (like the car having this problem at the top of the hill) sure sound like fuel starvation. The HS2s on the Mini have given me fits where they would sometimes stick shut even when the valves were clean. When this happened the car would loose power, stutter, buck, and backfire. I got tired of getting out and hitting the float bowls with chunks of 2x4 and eventually replaced the float valves.

If you can stop safely when the problem is happening, it might pay to switch the ignition off and coast to a stop... then look in the float bowls to see how much fuel is there.

 

[Billm]

Rick
To me this really sounds like a fuel problem and I think that you need to run a 12 volt light bulb from the fuel pump up into the car so that you can see that there is power to the pump (I will bet that you see it go off and on often). Bill in Kelso just had the same symptoms last summer and found a wire that had been ready to break for a long time and finally did.
Bill

 

[RickB]

Thanks Bill, I probably should have gotten under there today and looked. You may be right it might just be a wire.

 

[RickB]

Yesterday I put in the Facet fuel pump to see if I was getting proper fuel delivery.

The additional fuel pump did not fix the problem.
This morning was not as bad as yesterday, however it was not good.

This usually happens when the car is started after sitting a while, yesterday afternoon was the exception. Yesterday it ran great at first then after a good hard run between Issaquah and Snoqualmie it started having trouble at the flat area where Highway 18 meets I-90.

Where it always happens is at home first thing in the morning.
The conditions are:

5:00AM it is dark and about 35F.
Engine starts, but runs rough with or without choke on.
Pull onto street and it starts missing, if I give it more gas then it will pop and sputter.

I let it idle a minute, then I can go a bit farther.
Getting up to speed, about 30 mph, if it starts to pop & miss and I give it more pedal it will backfire.

Pull off the road, turn engine off, wait a minute, start engine and pull away.
Rinse & Repeat.

Eventually (every day) it has straightened out and ran good enough to drive it to work. This is at Interstate highway speeds, then I get off the highway and drive about a half mile on surface streets about 25 mph to the office.

This morning it missed a few times on the freeway, but nothing bad.

Maybe there is a stuck valve in a float chamber, I will take them apart tonight.

I removed the inline fuel filter and put the facet pump in its place. The filter had no restrictions to flow.

 

[jlaird]

Did you replace that coil with the loose top yet?

 

[RickB]

No Jack - I've been all over the place on this one. Can I just get any coil from the local Autozone? What fits? They won't have this in their computer will they?
I'll check PartsAmerica.com and see what they have.

 

[RickB]

Maybe I'll pop the coil off my MGC & put it on here just to rule that out (or in).
I guess I could also use the one from my Midget. That's actually easier so I'll try that one.

At lunchtime I pulled the tops off the float bowls.
Looks perfect in there, still clean too thanks to the filter I put in after cleaning them last time. The valves are operating correctly.

One of the backfires blew a 2 inch hole out of the bottom of the muffler.
The car is a wee bit too loud now. :wink:
The muffler was rusty, so the metal was weak.

The cap & wires are relatively new, all bought this year.
I'll keep looking and checking all the suggestions as long as you all want to keep giving them or until this is fixed.

Just a weird thought: My tach is dropping out randomly, just drops like a rock to zero then pops back up etc... that couldn't be a factor here could it?
I've found that when it doesn't work I can tug on the white wire that comes out the back and it starts working again.
I'm reaching for anything here...