Battery light flickering, RPMS go to 0 while at expressway speeds

[Foxyman315]

Hey all! I just joined and I searched so I'm thinking I might have an alternator issue but it doesn't fit some of the other threads on here.

I just did a longer drive (50 miles) with my 2002 Saturn SL2 with 140k miles. It drives great but when trying to keep up at 70 MPH the battery light will flash and RPMS drop to zero. It it is a complete loss of acceleration for a moment. I had the battery and alternator tested and both show strong but of course it is not under pressure while the test is being done. I did buy an alternator but I'm not sure that's it. Battery light only flashes for a moment and then goes away. Any thoughts?

[Waiex191]

I'd check the power and ground connections from the battery for security and corrosion.

[Foxyman315]

Originally Posted by Waiex191

I'd check the power and ground connections from the battery for security and corrosion.

Will do, thanks!

[billr]

"RPMS drop to zero"

Clarify that: does the tachometer reading drop to zero, or does the engine stop rotating. I think you mean the tach, as having the engine stop dead at 70 mph would be a rather dramatic event... But I would like to be sure I understand correctly.

[Foxyman315]

Originally Posted by billr

"RPMS drop to zero"

Clarify that: does the tachometer reading drop to zero, or does the engine stop rotating. I think you mean the tach, as having the engine stop dead at 70 mph would be a rather dramatic event... But I would like to be sure I understand correctly.

Vehicle still rolls but zero acceleration and it shows zero on the tachometer. Engine still running but zero response to the gas pedal. Radio and all still work.

[billr]

Does it come back alive as the car slows down from 70? No codes being set? Yes, get it scanned for codes even if the CEL/MIL light is not coming on.

Is this an intermittent problem, only happens occasionally and you can often operate at 70 or more with no problem?

[Foxyman315]

Originally Posted by billr

Does it come back alive as the car slows down from 70? No codes being set? Yes, get it scanned for codes even if the CEL/MIL light is not coming on.

It can be going 75 without issues so it doesn't seem to be speed, however it only does it in the higher RPMS (3000 or close). Getting it scanned soon.

[trottida]

A loose battery post wire would drop all current so all electronics would go dead and all your gauge cluster would be dead. In your case you indicated that the radio and all stayed on. Since you mention the battery warning lamp is on, I'm assuming that your gauge cluster is working. A tachometer with a zero reading indicates to me that your engine has no spark or the signal from the PCM has been lost.

With the above in mind I would look specifically for loose power and ground connections associated with the engine. The battery warning light is indicating low or no voltage and it's likely coming from the PCM.

Are you sure your engine is still on? It may still be rotating from the momentum passed through from the drive train.

[Foxyman315]

Originally Posted by trottida

A loose battery post wire would drop all current so all electronics would go dead and all your gauge cluster would be dead. In your case you indicated that the radio and all stayed on. Since you mention the battery warning lamp is on, I'm assuming that your gauge cluster is working. A tachometer with a zero reading indicates to me that your engine has no spark or the signal from the PCM has been lost.

With the above in mind I would look specifically for loose power and ground connections associated with the engine. The battery warning light is indicating low or no voltage and it's likely coming from the PCM.

Are you sure your engine is still on? It may still be rotating from the momentum passed through from the drive train.

So to be honest I'm not 100% sure if the engine is still on. The grounds look pretty rusted so I'll start with cleaning those.

[fdryer]

Originally Posted by Foxyman315

..... 2002 Saturn SL2 with 140k miles. It drives great but .... at 70 MPH the battery light will flash and RPMS drop to zero. It it is a complete loss of acceleration for a moment. I had the battery and alternator tested and both show strong but of course it is not under pressure while the test is being done...... Battery light only flashes for a moment and then goes away. Any thoughts?

I think you're mistaken with auto store battery/alternator tests. Most, if not all battery/alternator testing equipment used on vehicles or in-store, always places a large electrical load on either battery or alternator to stress test them for immediate evaluation.

One example would be a battery placed under load between 175-300 amps (depending on the CCA rating of a battery) for 15 seconds (similar to starter current). Translated, a battery load tester will pull 175-300 amps using heating elements similar to toasters to test how well a battery will output then measure voltage after the test is done to determine battery status; good, partially discharged or near its end of life. Alternators are tested similarly by placing a load on the electrical system like the battery test to see if the alternator will maintain its best output, between 13v-15v. Whether in-car or bench testing, auto stores (reputable ones) provide free testing as a courtesy in hopes of customers buying parts regardless of testing outcome. Dishonest stores may try upselling battery and/or alternator. Buyer beware.

I'm with trottida about possible (severe) corrosion on battery connections (battery positive and two battery negative - battery to chassis, chassis to engine block). Hopefully this is all that's wrong and easily cleaned up (dried battery acid dissolves easily with a solution of warm water and baking soda with a toothbrush as it bubbles immediately, water rinse). Vaseline or grease applied to bare connections delay future corrosion.

[billr]

Battery connections alone won't account for this. A properly operating alternator will keep the engine running even if the battery is completely removed.

[Waiex191]

Originally Posted by billr

Battery connections alone won't account for this. A properly operating alternator will keep the engine running even if the battery is completely removed.

Alternator -> starter -> battery -> UHJB

I'm pretty sure that is the connection order

[billr]

OK, I see what you are getting at, but it is actually like this:

Alt>starter>bat cable>split to bat and UHJB.

If the battery positive cable is OK up to terminal and its split, then the battery can be disconnected without killing the engine.

That is how my gen1s are constructed. Are later years different?

[Waiex191]

Same for my '98 and '99. But if the terminal on the starter or the UHJB is flakey, or anywhere on the positive cable, power can be interrupted to the system.

[billr]

Since the radio and other stuff do not die, all those alt/starter/cable/UHJB connections are probably OK. I'm not saying to ignore grounds or the battery side connections, only that we should not get fixated on those. The radio that keeps working shows that the UHJB is powered up by some path, whether by the alt or battery or both is of little interest for solving the engine-die problem..

[Foxyman315]

Originally Posted by billr

Since the radio and other stuff do not die, all those alt/starter/cable/UHJB connections are probably OK. I'm not saying to ignore grounds or the battery side connections, only that we should not get fixated on those. The radio that keeps working shows that the UHJB is powered up by some path, whether by the alt or battery or both is of little interest for solving the engine-die problem..

So then any thoughts as to what it is?

[Foxyman315]

So...I'm thinking it might be that pully tensioner which would explain why it only happens at high RPMS.

[billr]

Please confirm: is it really intermittent, you can often drive along in the 70mph range with no problem? And, when the engine is dying, or going limp, other electrical stuff like the radio and heater-blower and lights are not affected?

Intermittent problems are hard to catch, especially if they only show up at 70MPH! Getting it scanned for codes is the next step. Be sure to look for "pending" codes and codes in history. No joy with that? Then connecting a fuel-pressure gauge and live-data scanner to observe while the engine is dying would be next; looking for an obvious change in the engine.

The symptoms, engine and tach dying, hint at a problem in the CKP sensing circuit. Check that cable for damage, maybe even throw a CKP sensor at it. I would expect some kind of CKP code to be set, though if that is the problem.

[billr]

I should note that a CKP problem probably would not cause the alternator light to flash. That hints at a problem with the ignition/run circuit. We really need to get the codes before further guessing.

[Foxyman315]

P0341 CMP Sensor Circuit Out of Range
P0401 Insufficient EGR Flow Detected
P0410 Secondary Air Injection System
P1584 Cruise Disabled Circuit Fault
P1599 CC Power Management Mode or Engine Stall