[Mgs] Stumbling / stalling ignition issue?

The Roxter rocknatural at gmail.com
Sat Apr 17 18:08:34 MDT 2010


David Ambrose wrote:
> On 4/17/2010 2:28 PM, Paul Root wrote:
>> Hi all,
>>     I just got back from a trip to and from work. Less than 20 miles 
>> each way. At
>> about 10 miles each way, I was getting some stumbling.
>>
>>     The terrain varied, slight incline/decline or flat. Speed was 
>> constant,
>> sometimes a lift off the throttle for traffic.
>>
>>     The symptoms were 3000-3500 rpm, the tach would bounce down to  
>> 1500-2000,
>> and then back up. A couple of times it dropped to 1000.
>>
>>     It happened 3 times in a row on the trip home, within about 3-4 
>> minutes, so I
>> was ready and paying attention. The ignition light did not come on, 
>> ever.
>>
>>     I decided after that to get off the highway and take surface 
>> roads the last 4
>> or so miles. And I got another stall at 2000-2500 rpm. I downshifted 
>> to 3rd
>> and the car restarted.
>>
>>     At a stoplight, the car did stall. It took 20-30 seconds of 
>> cranking to
>> start. Normally, the car starts within 10 seconds cold, and 2-3 
>> seconds warm.
>>
>>     I got home without further trouble.
>>
>>     The car is a 1977 MGB, I have a pertronix distributor, that I put 
>> on new last
>> year. A pertronix coil, that's 8-9 years old. Ignition wires are 8-9 
>> years
>> old. Dual SU (HIF) conversion.
>> Alternator replaced to summers ago.
>>
>>     I'm in the middle of my second tank of gas for the season, I did 
>> put in a can
>> of heat. The oil is fresh, changed last weekend.   Oh, as a side 
>> note. I used
>> NAPA high milage oil. It's made by Ashland, which is Valvoline. 
>> Anyway, it was
>> rated SL/SJ. Not SM. Napa Gold filter.
>>
>>     I recently put in a plumbing ball valve in place of the stock 
>> heater valve. I
>> don't see any leaking there, but I'll check it again. I do have to 
>> pull it
>> apart, I put the valve in backward for the cable to work.
>>
>>
>>     I'm going to go and do a fuel delivery test (1 imp qt per 
>> minute), and look
>> things up on Paul Hunt's web site. Oh, and check the rotor and cap.
>>
>>     What else?
>>    
> I think I've seen this before.....
>
> The bouncing tachometer points to a problem in the low tension 
> circuit. I would look for a loose or poor connection between the 
> distributor and the coil, or between the coil and the rest of the car. 
> Make sure the connections are clean and tight. This goes double for 
> any crimped connectors in the wiring harness. Make sure the connector 
> to the distributor is tight.
>
> You may be able to diagnose the problem by connecting a test light to 
> the distributor and wiggling wires. 
Other possibility: Ignition switch.

-Rocky Frisco
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