Engine makes faint intrmitnt thumping - pulls down idle (rough), alternator overheats

[Fivefingerdeathpunch]

Do you have a scanner that could watch fuel trims?

That would be the best way to see if a vacuum leak is present.

Perhaps even undo the oil cap while running, see if it sucks your hand in.

[sheepdoggie]

Do you have a scanner that could watch fuel trims?

That would be the best way to see if a vacuum leak is present.

Perhaps even undo the oil cap while running, see if it sucks your hand in.

Thanks for the reply! I would love to have one of those scanners for android phone. Do you know what the most popular or recommended one is?

I have tried my best to eliminate vacuum leaks as being an issue but I don't know all of the places to check. I'll describe what I have checked so far:

Had to JB Weld a crack in the lower intake so was able to check the lim gaskets are in perfect order. The plenum gasket looked fine as well, there was no point in even changing it. The throttle body gasket seems to get compressed at the bottom (have had major leak there before), so I swapped it for a new one while reassembling. I fabricated a blockoff plate for the EGR to try eliminate it for testing. EGR pipe and lim passage look OK. I have tried removing the brake booster vacuum line and plugging it with a cork . No change. The throttle body vacuum port looks good, connection doesn't appear to leak, line OK to fuel pressure regulator and purge solenoid. I have sprayed carb cleaner all over and found nothing. I just tried putting my hand over the open oil port and did not notice any suction.

One thing I had not considered. When I fired the car up to do the test I noticed that it seems to get more rough again at the 4 minute mark which seemed to correspond with a really quite loud internal whistling noise. I put my ear all around the intake and it really seems to be loudest right above vacuum/EGR ports of the Plenum (closest to throttle body). I would not be the least bit surprised if this was two separate issues, but some kind of vacuum leak here (if it is) must be eliminated to move on. I heard that EGR gasses often melt the plenum channels, I will try to search online about that issue. Any recommendations for what I should look for? Is there any way possible that this could be related to the alternator overheating?

[sheepdoggie]

Have done a bit of research. If the plastic coolant and EGR channels in the intake manifold have been melted or breached by hot EGR gasses, the standard fix I guess would be to replace it. I found it for only $65 on rock auto which has a fix to prevent it from happening again. Another forum post about this. I know that coolant is carried to the TB, and EGR gasses are passed through, but how will this cause a vacuum leak (or the whistling sound I hear)? This could be related to the delayed throttle reaction with *PSSSSt* sound.

I have to confess that money is a constraint and I have already spent quite a bit getting it this far. Is there a way that I can test by blocking off the plenum passages? Or is there some way or telling for sure this is the issue, or perhaps a temporary repair just to see if everything runs well. Edit: I found a workaround fix that I might be able to try. If the alternator issue is totally separate, I need to know that I have a good plan in place to make all repairs with better known costs. Thanks.

[sheepdoggie]

I have checked over the underhood fuse box and the glove compartment fuse box and ensured that there is continuity on each fuse.

I have been operating under the assumption that the alternator is overheating because an excessive load or short is being placed on it. Is there another possible cause?

If no fuse has been blown, this means that all circuits that are being protected by these fuses are operating within standard current flow.

I believe the alternator is 110amp. It would take at least a couple of the big amp circuits in the underhood fuse box, or a majority of the large circuits in the glove compartment fuse box to consume the alternator's full capacity. Correct me if I'm wrong, just guessing here. This would point to the common areas to look at, like where multiple circuits share a ground mounting point. If one of these grounding points is damaged it may cause resistance in the circuit which acts like a load and takes a share of voltage. I think this can be tested by checking voltage drop of a live powered component, but I wouldn't know which to test, and if its even detectable outside of a severe engine bogging event.

I think a typical course of action might be to remove all unnecessary fuses, and start the car to see if a bad circuit has been eliminated. Most of the glove box fuses it look like they can go. Is there anything which is important to leave in while running the car? Many of the underhood ones seem more important. Here are some diagrams that seem to be accurate to the car.

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Questions:
What are the possible causes of an overheating alternator?
Are there more ground points which I need to check? How do I find them?
What is the bare minimum set of required fuses to run the car?
Are there any other standard tests that can be done with a multimeter (10amp ammeter)?

I appreciate the views and help so far.

[sheepdoggie]

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Didn't post properly.

[sheepdoggie]

I have continued to pull it apart and test some things and I think I may have some new theories.

First, let me go over some of the recent tests and results:

* Pulled the upper intake off and inspected the gasket, and the coolant passages near the EGR.
The plenum gasket was replaced a couple years ago when doing the lower intake. It appears to be flattened in some of the coolant passage areas near the EGR. The mating surface to the lower intake, and to the throttle body appears to be somewhat warped, however, it doesn't appear to be bad enough to cause a gap. The actual integrity of the channels appears to be perfect, there are no holes or leaks in the coolant passages. Cleaned and polished mating surfaces and replaced plenum and throttle body gaskets. I cannot imagine a leak happening here.

* Tested amperage draw of car turned off, and turned on.
The battery has been sitting for a few days inactive and measured a 12.63Volts charge. With my 10A multimeter, I removed the negative post on the battery and bridged the gap with the meter in amp mode. Locks can be heard cycling, etc. Fluctuating around 6 amps for 10-15 secs maybe and then slowly settling down. I believe it was at 0.035 amps after about a minute where it remained. I purchased a fork type 100amp meter and used this to check the flow while the car was running. I detected 55 amp draw while the vehicle was running and this was fairly consistent, perhaps jumping around + or - 5 amps. I only ran the car for 5 minutes before the alternator was too hot to touch. Is 55 amps normal? Seems excessive since I read that charging the battery will take less than 10 amps.

* Tested coil packs (in progress)
I tested the resistance of all 3 coil packs at the main post which goes to the spark plugs. Two of them measured exactly 5.92 KOhm, and the third measured 5.81. I was unable to get the probes into the slots for the lower resistance coils and will have to figure that one out with some wire or something. I also plan to run the engine and pull and replace plugs one at a time to see if the intermittent engine bogging becomes steady. (EDIT: I read that this was a great idea. However, the hard way taught me that it wasn't so much. In the time it took me to panic, I saw maybe 10 arcs of lightning hit in all different directions with bolts of what seemed like at most 2 inches one of which used my conveniently placed finger and welding glove to find its way to ground. Didn't hurt too much but the remaining five plugs could be summarized as: NOPE. The engine took it really bad and I think would have died had I not turned the ignition off.)

I have a theory which could explain the mode of failure. Bad grounding (it was very corroded in many major points) may have caused damage to the ICM or coil packs. I am not sure how this ties into the 55 amp draw and overheating alternator as I have fixed the ground points. It is possibly just a bad alternator throwing me for a loop.

Questions:
Is 55 amps too much for a typical running vehicle? If so next step is to use the ammeter to isolate which circuit is loaded up.
Is a .11KOhm resistance typical deviation, or could indicate a problem?

[sheepdoggie]

Latest tests:

Current draw into main use box from alternator 35-40Amps (cant say why its not reading 55 any more).
Current on link from main fuse box daisy chain to battery 2-3Amps
Voltage at alternator output 14.4V
Voltage at main fuse box 14.25V
Battery at ignition off 12.63V

Coil packs. Main posts 6.09kohm, 6.2kohm, and 6.0kohm (spec 5k-8k). Other coils 0.4ohm, 0.4ohm and 0.4ohm. (spec 0.5 – 0.9) IS THIS BAD? Every time I try measure it starts at 0.0 ohm and counts up 0.1, 0.2, 0.3, and 0.4 over course of a few seconds. Sometimes I dont think I get a good connection and it blasts up to 1.9ohm and back down kind of going all over and settling down below 1 ohm)

Putting the ammeter above the IGN relay, I am showing about 15 amps, but it is not the proper way to use the meter and I don't know if its accurate. Shows the fuel pump at about 5-6 Amps, and the rest don't seem to be drawing much at all but it's difficult to get a proper reading.

I unplugged the MAF sensor and this causes the rpm to exaggerate the bogging cycle. Instead of bumping up and down within a range of less than 50 rpm (hardly noticeable), it drops and surges in a range of 200-300rpm consistently.

The voltage remains steady according to my digital multimeter. If it truly is steady, and not fluctuating too fast to be picked up, then I am assuming that the electrical system is supplying a clean signal and a power drain is not the direct cause of the bogging. Perhaps someone can shed some light on what the next steps might be. I am almost starting to think that live data will be 10x easier than scouring every last part for a problem... suggestions appreciated.