90 300S starting hard all the sudden.

[C Holmes]

I have a 300 S and when I brought it out of storage it started right up and ran fine, when I jumped in to go for a spin I stepped on the gas and she coughed and stalled. I had quite a time getting it going again but when it did go it would do the same thing. I managed to get it too the gas station and put in some high test thinking bad gas but almost never made it back. If I let it sit awhile it will start and idle but when I try to rev it up quick it will stall and be very hard to start after that. I will say it was working perfect when I put it away last fall. Anyone know where I could start to look? I will mention I think the alternator is not charging as the ABS is on and it tests as only putting out 12.6V. The low charge condition should not effect the engine running properly or would it? I have a new Voltage regulator to try to see if it is that or the Alt. itself.

[Ferdman]

Remove the voltage regulator and compare the length of the brushes with the those of the new voltage regulator. Worn brushes prevent the battery from recharging properly.

[C Holmes]

You mean by all means it will keep it from running properly? I have removed it and the brushes are worn out so I will replace the VR

[Ferdman]

Yes, if the battery is not recharging the engine will not run properly.

While driving our 1991 300CE several of the dash warning lights came on simultaneously and the engine started to run poorly. A short time later the engine simply died. Jumping the battery would permit the car to be driven a few miles until the engine died. Turned out the voltage regulator brushes were worn down to nubs preventing the battery from recharging adequately.

[C Holmes]

I will let you know what happens when I change the VR

[Cal Learner]

Fred, it is certainly correct that worn VR brushes will have the effect you described and keep the engine from running right. But the reason for that isn't that the battery is not being recharged (which is true), but rather that the engine isn't getting sufficient electrical power from the alternator to keep it running. A low battery is merely another symptom of that condition. Isn't that it, or have I misunderstood that all these years?

[Ferdman]

Cal, you are correct, but I didn't want to complicate matters. I recall disconnecting the battery in my 1972 Chevelle with the engine running, and it stayed running because the alternator output satisfied the engine's electrical needs.