JENSPORT

I have a 1990 chevy silverado 350. About a month ago the idle got real ruff the volts went down and so did the oil pressure. The service engine light came on then went out and would come on again. If you turned on the headlights, the radio, or the heat the idle would get worse. I took it to my mechanic and the scan code was 43 esc module. I had one from my other truck he changed it and it was good for about 2 weeks and the problems came back again. I put another esc module on because the same the same code came up. This time it didn't help. I read somewhere it could be the knock sensor causing these same problems. Does anyone know if this is true? My mechanic believes its an electrical problem and if it is it's going to cost me a fortune because I know nothing about electrical. Any ideas

qldit

Good Evening JENSPORT, I am not familiar with that vehicle but your description would suggest you have either a battery or alternator problem.

Can you use a meter (if not it is time to learn!!) and measure the voltage across the battery terminals whilst the vehicle is standing without the engine running and then observe the voltage during it being started, then watch the voltage with the engine running at a fast idle kind of engine speed for several minutes. (it should slowly increase)

A simple meter is all that is required and they are cheap and simple to use. You will probably get one for less than $10 if you look around.

The voltage you would expect to see on the battery when the vehicle has been left for several hours would be in the order of 12 volts, during cranking the reading should not drop below 9 volts and when the engine has been running for several minutes at a fast idle should be in the order of 14 volts.

You might mention if these kind of readings are not achieved.

Chances are your oil pressure gauge is an electric type, so that would be expected to drop with very low voltage, the same applies for idling rough with extra items switched on.

At a guess I think you may need another alternator but the voltages you will measure will give a better idea.

Ensure your battery is properly topped up with distilled water to the bottom of the split rings in each cell. Do not overfill them.

If you haven't used a meter before you are about to have a crash course, to measure direct current (DC) which you will be, use the DC range in the area of 20 volts.
Put the meter red test lead to the positive battery terminal and the black lead to the negative terminal, the meter should then begin to read the info we need.

Hold the probes tight to the actual lead terminals (you won't get a shock or anything) and have a helper do the rest of the procedures.

The meter can also be used for other things but for this exercise you will not be using the resistance or AC ranges, ensure they are not selected for this activity.

Cheers, qldit.

JENSPORT

You have a valid point, but I read on another forum that it could be the knock sensor because that code 43 could show for that or the esc module and that was already replaced. I guess I could take the alternator to the auto parts store and have it tested. Thanks

qldit

Good Evening JENSPORT, I might suggest when a low voltage problem exists any codes may be false.
This could also explain your dash light indication.
The low voltage situation you described may be due to either a defective battery or an alternator.
This kind of thing could also be affected by a problem between the battery and the vehicle systems.

The alternator may also have an intermittent problem, your description of the vehicle voltmeter reading low would tend to suggest there is a problem in this area.

I would be inclined to check it in the vehicle, but any thing is better than nothing, I would also suggest having a battery capacity test.

Cheers, qldit.

jaggerwild

Hey JENSPORT!
You will not have to take out the alt to have them check it, just take the truck to the parts store ask them to load test it.
The code could be stuck in there cause of the faulty alt like qldit was saying. Also the code will not just go away it has to be removed with a scanner unit.
Think the knock sensor is cheaper than the mechanic's ideal, if it's not the problem then take the part back tell them you don't need it.
Hope we helped you, if so let us know.

JENSPORT

Thanks for your help guys I am going to the mechanics tomorrow to check the alt. I will let you know thanks again.

JENSPORT

Well guys we were both wrong. It's not the alt or the code 43. There are 2 wires that go to an external light that comes on these trucks. The wires must have touched the manifold and burned which shorted out the system. We just started wiggling wires last night and that's how we found it. Thanks for all you help anyway.

qldit

Good Afternoon JENSPORT, well done finding that problem!
I must get my long distance Xray vision re adjusted!! LOL!!

Wiring defects like that, kind of point to poor design and visual inspections not being good enough.
That kind of thing should not happen!

Cheers, qldit.

jaggerwild

Glade to hear!
So it's fixed then right?

JENSPORT

Well i thought it was fixed the problems have come back today. I have already changed the alternator and the computer and the problem persists. If I am running on the interstate at a higher rpm all the gauges are fine. When I go slower or drive through town the voltage drops and it starts to miss even at idle. It is worse when the headlights are on.

qldit

Good Afternoon JENSPORT, it appear you have a low voltage problem, this could be caused by anything from the alternator output, the battery cabling etc to the vehicle system.
You need to measure all the voltages to try to see what is actually happening.

This could even be caused by a faulty battery connecting lead, a fusible link or a problem with the fuse block in the cab or under the bonnet.

Chances are if you take the machine for a short run with all the accessories and lights turned on, you might pick it by then stopping and feeling all possible electrical connections and leads for any apparent heat.

Power loss like this generates significant localised heating in the problem area simply by it's resistive nature.

That certainly is a nuisance problem.

Edit, In view of your mentioning the shorting leads you discovered were actually for light, I wouldn't be surprised if your problem were a connection on the back of the in-cab fuse panel.
But feel it for heat buildup before you do anything and ensure you have the battery disconnected it you decide to drop it for inspection.

Cheers, qldit.

Raylo

I recently had a wiring problem with my 1994 S10 4.3L 4x4 p/u. I kept blowing the "gages" fuse whenever I shifted my auto tranny from D to OD. I first thought it might have had something to do with the tranny electronic controls or solenoids. Naw...... It turned out to be that the cable protector and insulation on some wires on the main wiring harness coming out of the firewall into the engine compartment was near the auto trans shift linkge and had been worn away by the linkage. The linkage hits an apogee in the OD position and this would ground a wire creating a momentary dead short. I was able to slide in a new piece of cable protector and pull the bundle away from the linkage and all is well again. The bundle had apparently been routed improperly and was too close to the linkage. Only took 13 years to become obvious. :-/

Then I had a 1987 IROC Z Camaro. I bought it in Feb 1987. Then in June 1987 it started running hot in stop and go traffic. The car had 2 electric radiator fans. The one fan was supposed to come on at 215 or 220 and cycle off at 195 or so. The other fan was supposed to come on at 235 or so or whenever the A/C was on.

But the engine temp now was always going to 230+ but no higher. Turns out that the wires for the lower temp fan had been routed THROUGH the blades of the high temp fan, and the first time I used the A/C it sliced right through them. Unbelieveable.

Do we see a common theme here?? GM quality control.... or lack thereof.

qldit

Good Afternoon Raylo, you make a valid point!

I believe there was a survey done involving the exact days cars were built and an interesting finding was that vehicles produced on a Monday had a higher than average problem rate!!
Possibly overhung auto-workers!! LOL!!

Cheers, qldit.