Compression test and the MS
 

Gents,

I want to do a compression test. I have the Shop Manual procedure. Is there anything I could/should do with the Megasquirt to make the test easier or safer?

Thanks,

If you unplug the cam sensor it shouldn't fire the coils or injectors while cranking.

Thanks for the reply. It can't be that easy. If it was, why isn't disconnecting the cam position sensor part of the Shop Manual procedure? Just sayin'.

If you're running a megasquirt with NB triggers and sequential injection it is. Some OEM ECUs will fall back to batch injection and run off just a crank signal after a certain number of revolutions without a good cam signal. No idea if the NB ECU's did this, but if they did it would be a good reason not to put that in a shop manual procedure.

If you are so confident in the shop manual procedure why are you asking people to waste their time with responses here?

I thanked you for your reply, and asked an honest question. I did some searching and never saw anyone suggest disconnecting the cps. Blow me.

You need to remember shop manuals are written with lawyers in mind for safety, and idiots as mechanics. They often have steps that aren't necessary, but help cover their ass. The bottom line is you're trying to stop fuel from injecting, and there are multiple ways of achieving this. You could reach down and jump the starter with a screw driver without ever turning the ECU on, which is a perfectly acceptable method of cranking the engine. But that's not in the shop manual, is it?

I did not reject Spartan's input, I only commented it seemed too easy. The further explanation made sense. There was no reason to get testy.

I'm lazy. I hold WOT while cranking to disable the injectors and call it a day.

I don't want to say I like lazy, but I try to avoid messing underneath the dash without removing the seat. I'm too old for that sheet. It's been a while since I did a comp check, and I didn't grow more nimble since.

I like the idea of disconnecting the CPS. You don't even do that?

I think there might be a disconnect in our communication here. I just sit in the driver's seat and hold the gas pedal to the floor while cranking. Does the same thing as disconnecting the crank position sensor or unplugging all of the injectors. As long as the injectors aren't firing, you're golden.

Case in point: the S550 EcoBoost Mustang has a recall out to replace the fuel supply line to the high pressure fuel pump. It's a 10-12" tube that can be replaced entirely from the top of the engine bay. This is directly from the technical info in the recall document:

1. Remove the rear seat cushion. Follow Workshop Manual (WSM) procedures in Section 501-10B.
2. Disconnect the fuel pump driver module (FPDM) electrical connector. See Figure 1.
NOTE: The FPDM is located on the LH side, beneath the rear seat cushion. NOTE: On vehicles equipped with Gasoline Turbocharged Direct Injection (GTDI), running the engine with the FPDM disconnected will remove most of the pressure from both the low and high pressure sides of the system
3. Start the engine and allow it to idle until the engine stalls.
4. Turn the ignition switch to the off position.
5. Remove the nuts and the engine appearance cover. See Figure 2.
6. Disconnect the battery. Follow WSM procedures in Section 414-01.
7. Disconnect the fuel pressure sensor electrical connector. See Figure 3
8. Disconnect the fuel line-to-fuel rail spring lock coupling. Refer to Spring Lock Couplings in WSM Section 310-00A. See Figure 4.
9. Disconnect the high-pressure fuel pump fuel supply hose. Refer to Quick Release Coupling in WSM Section 310-00A. See Figure 5.

Or you can wrap a rag around the fuel line when disconnecting it. Your choice.

Edit: Sorry for the thread jack.

No worries. Stories like that could turn into a sticky...

To me that reads as you rejecting my input, but maybe that wasn't your intention. However, I'm not inclined to give you the benefit of the doubt considering you're the sort of man child that tells someone to blow them when they're trying to help you..

Holding WOT doesn't disable the coils. You could unplug the coils, but if you're going to do that why wouldn't you just do the cam sensor?

If you hadn't included this sentence, none of this angst would have happened.

I'm a dick. I admit it. I ask a lot of questions. Bob Weir wrote in Walk In The Sunshine "Just 'cause I say it, that don′t mean that it's so".

Alrighty then... I did the compression test. I pulled the coil pack since I have to swap out the transmission, I also disconnected the CPS per Spartan's recommendation. I gave you a cat. I used a Craftsman nine-piece set I've had for years, but can't find the manual to, so I don't know the model number.

#1 207, 225 Wet
#2 209, 217 Wet
#3 202, 216 Wet
#4 209, 217 Wet

I poured about a quarter cap of oil into each cylinder for the wet test. I can't swear that each got the same amount.

Seems too good to be true. I'm also pretty happy with the plugs, although I suppose the color is skewed by warming her up at idle since the transmission is blown.

Should I put the coil pack back on and run it?

Thanks,


https://cimg9.ibsrv.net/gimg/www.mia...61b85712cc.jpg

Looks just fine

I know. Even if the gauge is reading high, the difference between the cylinders is fantastic.

I purchased that engine in October 2018, after I grenaded an oil pump at Summit Point. It was a part-out motor from The Parts Group. As far as I can count, I've put 127 track days on it. All of them Rotrex'ed.

Here's the longer story... I installed the Rotrex on the 135,000 mile original motor in May 2015. 8,000 miles later, but after an overheating incident due to a failed fan motor, she was down on power and using ~3 quarts of oil per track weekend. I believe it was early 2017 when I bought a JDM motor to replace it from a nice dealer in Manassas. It came with a six-speed for $1500. I left the original motor languishing in the garage on a furniture dolly. In late summer of 2018, I collected the parts to have the original engine rebuilt and took it down to a machine shop in Virginia Beach. I blew the oil pump on that JDM motor in Oct 2018, with the best events of the season still to come, and no way I'd get the rebuilt motor back in time, so I bought that part-out motor from The Parts Group. My rebuilt, forged rod and piston motor has been on an engine stand in my garage, wrapped in plastic, since late 2018.