Engine stumble while accelerating

I did a search for stumble and came up with some stuff to try but I still have a stumble.

Just yesterday on the freeway I noticed the car was missing every once in a while on my way to work. On my way home from work it missed more and more. The car starts just fine cold or hot and idles good too. I can rev it up while in Park and I don't think I hear the stumble or miss. When I go down the road the engine stumbles and misses. If I nail the gas pedal it really stumbles and backfires.

Here's what I've done: Bought new spark plugs, plug wires and fuel filter. One year ago it got a new cap, rotor and points. I tried to check the plus side voltage of the coil put my multimeter has a blown fuse.

I did notice when I hold the brake and push the gas (while at a stop) the lights dim/flicker when the car stumbles. Could this be a sign of a failing altenator or does this sound like other issues? Sorry this is so long. I just need to resolve this this weekend.

 

Sounds like a air/fuel ratio problem, if it was ignition it would run rough at idle also. First two things I'd check would be is the choke opening all the way, or is the fuel pump operating up to snuff. You can just look at the choke but you'll have to have a fuel pressure gauge or another pump to try.

Dave Berry

 

The choke looked all the way open and the air filter is brand new. If I did get a fuel pressure gauge, what psi should I expect?

 

You know I'm not really sure with a stock pump, which I'm guessing you have, around 4 to 5 psi at idle maybe. Hopefully someone will chime in here that really knows. ou:

Dave B

 

how old is the coil? its sounds like you have a bad coil to me

 

As far as I can tell the coil is original. Is there a way to check it with a multimeter? I was trying to check the positive side to see if it was receiving the correct voltage but should I be checking the negative side to see if it's sending correctly instead?

 

mark from what you say it is missing only under a load ok os that tells us thatit is either thethe vacumn advance moving in the dis causing a short of some kind///this is easy to check remove the hose from the dis and plug it//if the problem is still there that eliminates that/ thencheck the cap and rotor for cracks /// another easy check it to have someone run the car in gear at nite you look at the plug/ cap and coil as they put a load on the eng like brake torquing if it misses you should see it ok/////if that doesnt show anything then it could be fuel////and you will need a gauge to test the pump as the guys are saying//////but what bothers me is you say it back fires thats why id check the ignition frist luck pete

 

A weak electrical system can do that. Check that Alt.

 

Now that I've had another look at it let me update and clarify.

It stumbles under load and while cruising on the highway but not during idle. While it idles the interior lights will flicker here and there. I checked the voltages at around 1800-2000 rpms and I get 12.5 on the positive side of the coil and about 10 on the negative. During idle I get around 6 volts on the negative side. I didn't get to check the cap for cracks or the vac advance yet.

The only reason I suspected the alt was I had a Nissan truck that acted the same way and I drove it for two days that way until it died. It was the alt.

I appreciate all the suggestions. I'm getting the alternator checked in the morning and I'll update after that.
MARK

 

mark one quick way to ch the alt is start it run it at a fast idle and pul a batt cable if it dies alt isnt putting out ok/////most auto stores will ck it for free too later pete

 

Thanks Pete. Will do.

 

I also think you have a bad coil.

Get one from NAPA. I believe you want model IC10.

They are cheap and when mine went bad it ran the same way.

 

I tested the Alt at Advance Auto Parts and it's good. One of the guys there showed me how to test the coil with an ohm meter and I got 1.5 ohm between the plus and minus side of the coil and 11.85 kohm between the plus and the main dist. wire. He said those were within spec. I found a broken wire that goes to the plus side of the coil and somewhere else (see pic). I repaired it but am still having the same issue.

I last filled up my gas tank at Kroger. Could it just be bad freaking gas or would that effect the idle speed too?

 

Bad gas is a possibility, but I'd say that it would only compound a problem somewhere else. Bad points could do it, or if the timing was off a touch. It is in the electronics somewhere.

 

Mechanical advance was working about 2 months ago when I set the initial timing to 12 but I don't remember my total. The vac advance works. I plugged the port on the carb and sucked on the hose that goes to the canister. It increased the timing.

I'll mess around with the timing more tomorrow and try to get some definite numbers. I have a hockey game to go to tonight!

 

I pulled the distributor and found all this powdery stuff in it. uzzled:

 

There was also white stuff all over this area of the dist. When I wiped off the powder I found black tar-like goop caked on it. I scraped all that off and cleaned it back to bare smooth metal. When I dropped the distributor back in the car I couldn't get it to line up like I had it so now I'm trying to get it fired again. Unfortunately, my wife had me running all over today so I never got the car started.

Something else I noticed when I changed the plugs and wires was two of the spark plug wires weren't even touching the contacts in the dist. The spark was just arcing about a 1/2 inch and a lot of black soot had built up.

 

For the backfire problem, wouldnt the timingchain be a problem?

 

Oh, I seriously hope not, but yes a possibility. I only here the backfire when I stomp the gas pedal. I'll know more tonight after I get home and get it fired up again.