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Looks like I might have an alternator issue developing. Was out tuning this weekend and after the car got heat soaked it started running like crap. I was logging the battery voltage and it showed a maximum of 13.5 volts and dropping as low as 12.9. These were reading on the Sharktuner.
When I got home I checked the voltages while hot and the jump post showed 13.3 v. I cleaned all but the alternator connections and then rechecked the voltages cold. At idle the jump post was reading 13.9, battery 13.9 and the Sharktuner 13.5. At 2000 rpm nothing changed substantially.
So. I am thinking my next step is to drop the alternator and have it benched tested (it is the original).
But the other question is why is there such a big discrepancy (0.4 volts) between the jump post and Sharktuner readings?
Shark Tuner displays actual voltage as seen by the LH/EZK, why it's lower could be a number of reasons.
The LH/EZK are fed directly from the connections on the battery. That clump of wires attached to the post. Years ago we had a very random intermittent issue with an 87. Long story short, after a lot of troubleshooting, that nut on the battery wasn't tight. It wasn't loose, but only finger tight. Tightening that down instantly fixed the problem.
So, maybe take that all apart and clean up the connections on the battery, a place to start.
I do not see anything there that suggests a major issue. The sharktuner power connection is deeper into the system so more voltage drop at the point of supply- how much obviously depends on the connected load.
Under some load conditions like not enough revs with lights and air conditioning/fans running you might see the voltage drop below 12 volts if the battery is discharging to support whatever is being generated. Even then the engine should run just fine.
Whether or not you have a separate coincidental performance issue is another matter
Ralph, a voltage drop of 0.4v from jump post to Sharktuner is typical, that's the drop through the wiring, relays, connectors etc to the LH circuit board. The LH itself runs fine down to fairly low voltages-- it has to, for cranking.
When it ran like crap was it moving and getting fresh air, or stationary? Was the AFR OK? I've seen intake temps go as high as 70C on our GT (which has an intake air-temp sensor) just sitting. Engine runs fine (and the MAF corrects for air temp) but idle struggles, needs a lot more ISV. So if your ISV is close to max'ed (LH limit is around 68%) then that might be an issue (ISV should normally be in the 50-55% range).
Hi all,
Thanks for the replies.
Jim, I had just installed an air straightener ahead of the MAF and was retuning so I have one more variable involved. Will definitely need some more tuning time to figure this all out.
The worst symptom was coming to a stop when hot and the voltage at it lowest, 12.9-13.2. The car would consistently die and need to be restarted. Did not look at what the ISV was doing. Hopefully, I can get back to tuning it next weekend.
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The worst symptom was coming to a stop when hot and the voltage at it lowest, 12.9-13.2. The car would consistently die and need to be restarted. Did not look at what the ISV was doing. Hopefully, I can get back to tuning it next weekend.
Not voltage. What I suspect is happening is that you have gone outside the envelope of what the LH idle-control can handle (the part of the LH code that handles the ISV). For stock motors, the stock idle control works great but it is very much designed around how the stock motor responds. Things like that big whirligig on top of the engine is probably confusing it.
Sharktuner now includes a cosmic new idle controller as an option, with all sorts of "virtual *****" to play with. I'll send an email with info.
05-15-2017, 11:58 AM
sharktuner voltage reading and alternator issue
