Best way to disable ignition system for compression test?

Gang,

Trying to perform a compression test on my 355. One needs to disable the ignition system so as to not send spark and/or fuel to the cylinders. There are a variety of ways to do this but I haven't seen any clear direction here re: the 355.

I thought the easiest thing to do would be to simply disconnect the connector at the coil packs on both banks 1 and 2. Problem is that when I turned the battery cut-off switch to ON (I turned the battery cut-off to OFF when not driving the vehicle regularly) I had no power. I reconnect the connectors to the coil packs and I had power again but, alas, the ignition system was still not disabled.

What's the best approach here? Pull the fuel relay? What say the peanut gallery?

ketel

 

I've been wondering the same. I've read to pull the fuel relay and coil packs.

But, with an immobilizer (my starter cranks when armed), is any of that needed if the immobilizer is armed? Might be the best use of the immobilizer

 

I was just gonna say buy a 99 and your set!!!

 

Key off attach remote starter
One side to plug other to power coming in
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Just remove the plug wires from the plugs and remove all the plugs. Problem solved.


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On the 355/348 disconnect the harness connector at the coil modules, pull the fuel pump fuses, do your test. Easy as pie.

 

I bought an OTC remote starter, Tim

 

What's wrong with using the key?

 

The remote cost me $20 IIRC. The only problem using the key is my arms are not long enough to be at the bonnet holding the gage while inside the car cranking the engine, hence the reason they sell remote starters. But I'm guessing you already knew that

 

Ketel,

Considering your car's history I would leakdown it too.

 

You're still producing spark (which can present issues) and sending fuel into the cylnders. Not a good solution, from what I am gathering.

ketel

 

Nope. Did that. Cut all power to the vehicle that way.

 

You never want any electrical circuits energized during testing, can cause feedback some serious unwanted stuff to the ECU system.

Good boy you get cookie

A side note here keep your front hood open ready to shut the power off if needed
Cranking the started repeatedly can overheat it and cause the drive to stay in gauged and motor spins forever.

Let motor cool or tap with wood mallet or just remove clean and lube

Had this happen a few dozen times over the many years so be a boyscout and be prepared

 

No spark unless the wire is grounded somewhere. It's never caused a problem for me in 20 years.

Don't over think a simple task.

 

That is very strange. I do these tests weekly and never have I had a car not turn over.

348/355/456/550 all work the same way. One harness connector on the bottoms of the coil module(pack), and pull the 2 15 amp fuses for the fuel pumps.

 

Why not just pull the spade connector off the starter and jumper starter to pos terminal under the ps rain shield? No messing with fuses or pigtails, just one spade connector and you're on your way.

 

Because you need to disconnect spark and fuel thus the coil unplug and fuel pump fuse removal.

 

WSM
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Hey John,

Where did you find that? I looked all over the WSM...

 

More:
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No you don't, if you jumper the starter with the ignition off there's no spark or fuel to disable.

 

Got it.

Maybe Tbakowsky does use the key as he stated and that is why the WSM says to disable the relays.

I went back and looked at the videos I made of the CC I had done on that car at Algar. I wasn't watching where he put the leads but he did use a remote starter switch. Here are a couple screen grabs of the leads. You can see the one on the Positive on the engine bay posts and I am not sure where he tapped the starter on the left side but it looks like he has a blue wire connected to something and the other clip of the remote switch on that blue wire.

I don't recall him in the car fussing with that fuse panel but I wasn't really paying attention to that either.
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As I've been planning to do this with my car soon (out of pure curiosity), I know Tony at Algar so I will give him a call in the next week and chat with him about this.

There is also a chance I may be going there soon and if so, I'll talk to him in person about it.

 

On the starter there is a small wire with a plug and large wire with a bolt, thats +positive direct from the battery. Connect to both of them with a switch

All you do is energize the small wire to activate the starter. I have a small plug on one end of remote starter to make it easy.

Keep the hood open like I said in case the starter sticks on from overheating
Also keep a battery charger on it so you get no battery drain which can cause different readings beginning to end.

 

My process:

1. Bring engine to operating temperature
2. Install battery charger-maintainer
3. Connect remote starter (or remove Motronic relays per post 18-20 above)
4. Disconnect all spark plug wires
5. Remove all spark plugs
6. Install gauge into cylinder (M10x1.0), hand tighten
7. Open throttle completely
8. Crank for 5 revolutions
9. Record reading
10. Move on to next cylinder