OBD2 scanner

[Tom @ Fast Forward]

Lately we have had some problems with what appeared to be bad coils. A long time back I wrote a caveat the you need to double and triple check the tightness of the lower alternator bolt as it is the ground return for the alternator and low voltage can cause problems as well. Well, weak/bad coils are not always weak/bad coils. A bad ground at the lower alternator pivot bolt and/or the grounding of those three or four wires at the front of the engine that you move during install can do the same thing. When you move those 3-4 wires, make sure that they are connected to clean metal and bolted tight. One of those wires is the ground for the coils.

Those of you with OBD2 readers please do me a favor and monitor what the ECU thinks the voltage is and post it here. It appears that 14.5-15.0 is the norm. It can be as low as 14.1 or 14.2 but should not fall any lower. Low numbers could be an indication that one of those grounds is not good.

Power from a roots (eaton Magnuson) type blower should be a nice straight line. If your dyno chart shows a nice straight line up to 5000RPM or so and then starts to roll off, it is a good indicator of a possible coil problem.

Just curious what your OBD2 voltage readings are.

[gludlow]

I'll get mine when I can; brought it to a shop, since I started getting a P0420 code along with the Cyl3 misfire. So far they haven't found anything, nor do I expect them to unfortunately.

I'll have it back tomorrow and get the voltage readings.

[MX-Drew]

Well here are my figures, normal cruise, 14.2 - 14.4 volts.
This is the strange one, under boost, 14.5 - 14.6 volts.
Come off the throttle after the above, 14.1 - 14.2 volts.

These figures are so reproducible it is unbelievable.

For the record the alternator bolt is as tight as it can go with all mating surfaces cleaned before I put the alternator back on as I was aware of the problem. Also the earths at the front of the engine are made to very clean metal.

[gludlow]

Ok, I got some preliminary numbers.

Normal driving, between 14.2-14.5
On boost, a little higher (I saw 15 for a moment on one run) but usually 14.3-14.6
Off boost it drops, once I saw 13.8, but usually no lower than 14.0.

[peterc]

Guys can you tell me if your voltages drop when you have your foot on the brake, engine running. Mine drops anywhere from .2V to.5v and stays down until released.

[Tom @ Fast Forward]

Peter,

Idle at ~900 RPM, Volts at 14.5 relatively steady.

Turn lights on, Volts drop to 12.1 for just an instant (less than a second) then right back to 14.3.

With lights on, step on brakes, no change ~14.3.

With AC (blower fan on high, radiator fan and AC fan running), lights and brakes all on together, no change. ~14.3-14.5.

Only change was really the instant when the lights were turned on.

[peterc]

Thanks Tom. I will keep on checking the grounds.

On a side note, as a preliminary check of the voltage to the coils, I ran a wire from the 15amp engine fuse in the fuse box and monitored the voltage. That fuse feeds the coils. It was a pretty steady 13.9 ~14v WOT or cruising. I will try to get at the coil wires at the connectors, and see if there is any difference.

[Tom @ Fast Forward]

Peter,

When you did that check, where did you pick up your ground?

[peterc]

I used an alligator clip and got on to the edge of the cigarette lighter plug. It stayed on pretty good.

[peterc]

Tom,

are you thinking that I should have used the engine block since that's where the coil wires are grounded?

[Tom @ Fast Forward]

Not necessarily. What I was concerned about was that the rail has a green finish. Conductive? The block would be better but, if the rail finish is electrically conductive, it sjhould work as well.

Tom,

are you thinking that I should have used the engine block since that's where the coil wires are grounded?

[peterc]

Tom,

my cigarette lighter plug does not have this "green finish" and looks to be a good ground. I will use the engine block as gnd, when I check the votage at the coil connector.

[Tom @ Fast Forward]

My bad. I was talking about the fuel rail used for ground for those wires. That wasn't your car. Old age is setting in. That was the green finish I was talking about. My mind was on a different subject.

The gigarette lighter is fine for a test ground.

[peterc]

Tom,

I was able to get voltage readings directly from the coil connectors. I did one connector at a time. The voltages at these points is higher under boost, and more stable than the readings I get thru the ODB2 with the Scangauge. 14.2 to 14.3 left side. 14.1 to 14.2 on the right at the coils, Vs 13.8 to 13.9 thru the OBD2. Cruising the readings are the same from both sources. I wonder why under boost the OBD2 reading does not change on mine.

I also noticed that the voltage does not change at the coils when the brake pedal is pressed. The voltage drop (recorded at the OBD2) mostly only occurs for the brakes, and not other electrical devices, headlights, A/C. I changed the brake light bulbs, thinking there might be a short, but that did not help.

In case you are wondering how I got the reading at the coil connectors, I took a upholstery needle and inserted it in between the wire and rubber grommet until it made contact. The grommet kept it in place perfectly. I used the valve cover as a ground point. Wires ran under the hood into the cabin.

[Tom @ Fast Forward]

You should take the coil readings from the wires to the coils and not use the engine for ground. What we are trying to confirm is that the wire to the coils is as good as the engine ground. Should be a Black wire (GND) and a Black/White wire (12V) to each coil. You might have good voltage B/W to engine but not B/W to BLK? I know I'm being picky but............ :)

[gludlow]

Tom-
I spent an hour under my car; bought a hydraulic jack today so I was sorta playing with the new toy :-)

Anyway, I found out that removing the filter, unbolting the end of the air intake and pushing it back makes tightening the alternator pivot bolt a breeze. I tightened it down pretty good and put everything back together.

Now, my voltage rating is much more stable, as far as I can tell, but stable 14.4-14.2. It never dropped below 14 this time, but of course, I wasn't staring at it the whole time. Zoom zoom :-)

(Also, I'll add that I have a stereo amplifier, it was pumping pretty loud the whole time. I also disconnected the Bose amp, I think it helped with my static problem)

[Tom @ Fast Forward]

I sincerely hope you used jack stands.

Those numbers sound pretty good. How does it feel?

[gludlow]

I sincerely hope you used jack stands.

Those numbers sound pretty good. How does it feel?

Of course! I work for Caterpillar... safety first! Although I did discover that my pair of Farm & Fleet "paired" stands are actually about 5/8" different in height.

It feels good! But I'm not giving my final judgement until I get the high flow cat + resonator midpipe installed, assuming I have solved my CEL 3 misfire problem.

[Tom @ Fast Forward]

Are those the stamped steel/welded version or the cast version?

Well, it sounds good at the moment. Can't wait to see what happens with the high flow cat and back to the dyno.

[peterc]

Tom,

I finally had some time to get the readings directly from the +12V and Gnd wires at the coils. The voltage was 13.9V, about .2V lower than when measured from +12V at the coil and gnd at the valve cover, but the same as the readings with the Scan gauge. The voltage did increase to ~14.1-14.2V under boost. My voltage on the Scan gauge does not change under boost.

Last night I ran a new and separate gnd wire from the neg batt term to the chassis, and also replaced the gnd strap from the bell housing to chassis just to eliminate any doubt. It made no difference. I am planning to splice into the gnd wires at the coils and take them to another gnd.

I guess my next step will be to check / replace the pos wires, at alt, starter. I will keep after it in an effort to try and get the 14.5V that everyone else seems to achieve on their Scangauge reading. Maybe then I put it back on the dyno and see if I can find the missing WHP.

[Tom @ Fast Forward]

I don't think I would replace the wires. Just check all of the connections. That might not be the problem?

Sparkplugs still look nice tan/brown?

[peterc]

Have not pulled them out since the last dyn runs. I will take a look tonight.

[peterc]

Tom,

#1,3,4 look like this one. #2 is the same color brown all over. They look OK to me.

[Tom @ Fast Forward]

If anything, it looks just a touch rich and there is nothing wrong with that. Looks OK to me too.