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Old 08-19-2013, 03:55 AM
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HELP! Engine/Grounding problems.

Hello all, Hope someone can help me out here as I am stuck.

I serviced my Grand Cherokee 4.7 lit V8 a few weeks ago by changing oil/filter, sparkplugs and did an external enginewash (no highpressure).

The car started and ran perfect for a couple of days and then I left for hollidays for a couple of weeks. When back from hollidays I tried to start it and it would run normal for about 2-5 seconds and then as if only on a few cylinders and the exhaust smells very "fishy". What I also noticed was that the voltmeter showed 9 volts and the speedometer was moving erraticaly.

If I manage to rev the engine which is hardly posssible it starts kicking in and run normaly when passing above 2000rpm, however voltmeter and speedometer stays the same. All other indications are normal. I have checked the battery removing the connectors and it is 12.7 volt, generator gives above 15 volt when messured directly on the generator. messuring the battery terminals when connected and engine running gives just about 14 volt indicating the battery is getting charged.

Also the AC doesnt seem to work...doesnt cool but fan runs and AC light is illuminated.

It feels like a grounding problem to me so I have replaced the gronding cable I found under the rear of the engine running to the chassi and the exhaust. I also cleaned all small groundings I could find in the engineroom.

Are there any other major grounding points. And where is the ignitionbox located.

Would be eternally greatful for any advice.

Best regards,

Phil
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Old 08-19-2013, 12:03 PM
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Re: HELP! Engine/Grounding problems.

Welcome to the garage Phil.
I would have a look at the PCM ( powertraing control module= fuel and ignition controller) connectors for water ingress. Remove negative battery terminal before removing the PCM connectors. The PCM is mounted to the bulkhead.close to the right hand fender, just behind the coolant overflow reservoir.
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Old 08-19-2013, 04:37 PM
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Re: HELP! Engine/Grounding problems.

Thank you ever so much Frango. I will have a look at it more seriously. I did remove the connector to the PCM and put it back but no improvment. Does the PCM need to be connected to ground...could that be the issue? It is difficult to reach the screws but in that case I need to remove it and improve the grounding. If not it might just be faulty and need replacement. I can get one second hand for about 250/300USD.

Could it be worth replacing it if there isnt any gounding issue?
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Old 08-19-2013, 05:01 PM
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Re: HELP! Engine/Grounding problems.

I would say that it is too early to come to the conclusion that the PCM is faulty.
I won't expect a ground issue, since it was running fine before the vacation.
You mentioned the erratic speedometer and the low voltage indication. Do you have the SKIM light on on the instrument panel? (the key symbol with a line through it)?
Try first the keydance and see if any fault pops up (ignition switch off/run three times and leave in run at the third time. The odometer will show DONE when all ok, or a fault code.
You said you removed the PCM connector, but the PCM has three large connectors. Are you sure you took the PCM, and not the TCM, which only has one large connector and is just in front of the PCM?
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Old 08-19-2013, 05:16 PM
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Re: HELP! Engine/Grounding problems.

Quote:
Originally Posted by Frango100 View Post
I would say that it is too early to come to the conclusion that the PCM is faulty.
I won't expect a ground issue, since it was running fine before the vacation.
You mentioned the erratic speedometer and the low voltage indication. Do you have the SKIM light on on the instrument panel? (the key symbol with a line through it)?
Try first the keydance and see if any fault pops up (ignition switch off/run three times and leave in run at the third time. The odometer will show DONE when all ok, or a fault code.
You said you removed the PCM connector, but the PCM has three large connectors. Are you sure you took the PCM, and not the TCM, which only has one large connector and is just in front of the PCM?
I'd suspect whatever it is that controls the alternator if the voltage is truly that low.

I suggest picking up a small digital voltmeter somewhere. Radio Shack has a small one that comes with leads and a built in carrying case for a few bucks.

First, turn everything off, and measure voltage right at the battery posts.
If that's low, your battery could be flaking out, but I'd still suspect the charging ckt, so before you spring for a new one, borrow or pick up a charger and charge the battery. You should then see about 13.2 volts or a tad higher.

If the battery with everything off is about 12.7 volts, turn on the headlights and wait 2-3 minutes and check again... this indicates a failing battery that cannot hold a deep charge--called skin effect charge.

If all is good so far, start it up and see how the battery voltage matches the displayed voltage. They should be extremely close.

If you have a set of heavy jumpers, you can try jumping from the battery NEGATIVE terminal right to the body and see what happens to the display.

Or you can jump from that same terminal to the engine block.

Or, from the block to the body.

If you have something loose, one of those should bump the voltage to normal.

Seeing bad alternator control is a bit trickier, but at very low idle, hopefully you'll see a lower voltage as measured right across the battery terminals. Then, as rpm increases, you should go to in the range of 14 volts or just a bit above.

You can also put one lead of the voltmeter on the battery ground and another on the body and you should not see more than about 0.1 to 0.2 volts across whatever grounding cable you have. Same applies to measuring from battery ground to engine block.

You can also check from the battery positive post to your starter solenoid, again, no more than .1 to .2 even when cranking.

When doing any voltage check, don't touch the battery terminals, just the posts, as the terminals could have crud betwixt them and the post.

It might be worth trying an alternator or battery shop, they could make all these measurements in a couple minutes.

Good luck.
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Old 08-19-2013, 07:14 PM
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Re: HELP! Engine/Grounding problems.

Eventhough the PCM has the voltage regulator inside it, the voltage on the battery was measured at 12.7 V with engine off and the indicator showed 9V. According service manual the voltage indicator will go to min scale when the actual voltage is lower then 11 V. Also when the voltage signal input from the PCM, which goes via de PCI data bus, is missing, the voltage indicator will go to the minimum indication, which is 9 V. Also the speedometer input comes from the PCM ( which gets the info from the ABS controller), via the PCI data bus. My thoughts are going to water ingress into the PCI data bus connection somewhere.
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Old 08-20-2013, 02:14 AM
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Re: HELP! Engine/Grounding problems.

Hello Frango and Istowell!

Thanks a million for all suggestions. I have tried it all and this is the outcome:

1. The keydance gives only the indication: Done

2. The other Indications is a stedy lit engine symbol in amber and red "check gagues. and still 9 volt reading.

3. took connectors lose at the PCM and checked for humidity...nothing...sprayed with contact spray...no improvment.

4. I measured back and forth between posts and terminals vs block etc. and everything looks normal battery is 12.7 volts disconnected and when engine runs on idle (low due to related problem) and indicates between 13.3 and 15.6 volts.

5. I put a jumpcable between the negative terminal and the block, no change in any indications.

6. Messured resistans between engineblock and groundcable shoes (2) on lower part of engine (negative battery connection to engineblock. No resistance at all indicating a good connection.

7. Messured volt between negative terminal on battery and block, indicates between 0.01-0.03.

8. I also replaced the grounding cables between the exhaust, engineblock and body underneath the car...it was more or less without any contact...still no change.

I cant get my head around this problem but here are some things I find weird:

1. When starting the engine it runs normal for about 2-3 seconds (if it has been off for a period of time then its starts to sputter.

2. The exhaust smells like an old damp rag/fishy. As if the cathalytic process is inefective.

3. The odometer sort of flashes as the engine pulsates in idle...when engine sems it is about to stall the odometer blanks and immediately comes back as the engine revs back up to idle.

4. As I touch the throttle the engine hezitates and then almost stalls if I let the throttle lose the engne stabalizes for a fraction in almost normal idle just to drop back again and sputter.

5. If I manage to run the engine warm it stabalizes a bit and you can actually rev it up and drive. At high rpms it runs normal but all indications are the same.

Maybe it is the PCM? And how about the TCM what is that, which parts does it control?

Thank you for any advice....I am getting more and more pussled as we progress here.:bang head:

Best regards,

Phil
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Old 08-20-2013, 04:49 AM
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Re: HELP! Engine/Grounding problems.

The TCM is the transmission control module. Eventhough the PCM could be the problem, still other things can be as well and to just spend money without knowing for sure it will solve the problem, is not a good idea.
The instrument cluster gets most of the information for switching warning lights or the instruments via the PCI data bus. Voltage, speedo , rpm etc signal is coming from the PCM. Also the signal to switch the AC compressor on comes from the PCM.
It is so strange that the check engine light is on, but no faults stored. The check gauges light is on because of the low voltage indication. Did you already try to run the jeep with the alternator power lead removed, just to be sure that the problem is not related to the alternator?
Do you have a scanner or can you borrow one, which can show live data? Would be interresting to see what the battery voltage direct from the PCM would be. If it is still 9 V, then there seems to be something wrong with the PCM.
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Old 08-20-2013, 08:01 AM
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Re: HELP! Engine/Grounding problems.

Hello again Frank,

I was actually thinking the same as you now suggest and mainly because of the high voltage peaks from the alternator. i called Crysler today to try and get some info out of them but in vain. Ofcorse they want to have me tow the car there and spend megabucks just to learn they can offer me a new PCM for another 2000 USD.....No thanks!

The gentleman was however kind enough to tell me that the alternator current was far to high at peaks more than 1 volt above maximum. So this might be a problem. What controls the fieldcurrant to the alternator? Is it also the PCM?

I will run down now and take the cable of the alternator and see what happens...will report back shortly!

Phil
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Old 08-20-2013, 10:36 AM
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Re: HELP! Engine/Grounding problems.

Yep Frank!

Its the alternator output messing with the computer. I removed the cable and the car started and run perfect, a little bit unstable idle with a tendency to stall in the begining and also alot of blue smoke but I think this is just as the cylinders and exhaust is clearing from all the unburnt fuel. After about a minute no smoke and stable idle...no flickering of the odometer either. Nedless to say voltmeter at 9 volts....but no alternator connected so.

So now the question is where is the reguator to the alternator located...on the alternator itself? I would imagine I get a new regulator in stead of a whole new alternator.

Million thanks for all good advice...and Frank...you are a clever one!

Phil
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Old 08-20-2013, 11:18 AM
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Re: HELP! Engine/Grounding problems.

Hi Phil, the voltage regulator is part of the PCM. So not sure if this problem is caused by the voltage regulator, or the alternator itself. Clean the connector on the alternator first, to rule out any moisture or corrosion problem. I still have the engine wash in the back of my head and the alternator is partly open and water can easily penetrate in its interior.
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Old 08-20-2013, 02:11 PM
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Re: HELP! Engine/Grounding problems.

Hello Frank,

Just back from my garage, I took the alternator out and cleaned all the connections and contactors. Then I put it back and started the engine without the B+ cable attached. Everything worked smooth but no charge as you can imagine. When I connected the B+ cable again sparks flew from the cable and terminal on generator....I then decided to messure the alternator output without the cable attached and my voltmeter showed error so I selected AC units and it messured 65 volts AC!!!
I believe the transformer rectorfier unit on the alternator is defect ( the diods that is).

I guess it will be sheaper to replace the alternator to start with. What do you think?

Phil
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