First fire up after rebuild...only running on two cylinders

[BSF]

Hello,

I put my engine (3.6L in a 964) back in following a rebuild and went through all the initial checks... fuel pressure OK, cranked OK, built oil pressure OK (to prime the system), then it was time to hook up the coil wires and try to let it start.

I cranked it a few times and it wanted to start, and would fire a bit, but not get off the starter and idle. After about 5 tries it got off the starter and idled very rough and at a very low speed (~400rpm).

I got under the car and felt the header tubes to see how many cylinders had fired. Four of them were cold, and two were hot... so it had been running on two cylinders. The two that were hot were #1 and #2. (the two furthest from the flywheel on the drivers' side bank)

I know it can be a million things so I hesitate to even ask for ideas. I have a million new parts as part of the rebuild so I can eliminate very little as possibilities. I'm going to guess that it's more likely to be something in the ignition system rather than the fuel system. Here's a list, but what I'm really looking for is to hear if anyone else rebuilding a 3.6L had the same thing happen upon first fire.

1. Plug wires error
2. Distributor shaft clocking error
3. Something wrong with the flywheel trigger teeth (new flywheel) or the mag pickup sensor gap
4. DME error (I put in a new chip, required due to new injector size and MAF conversion)
5. A more critical error, like cam timing...

Thanks!
-Brock Fraser

[Groesbeck Hurricane]

Brock,

I would start with simple things like the plug wires. Distributor cap and rotor correctly installed, not cockeyed/lifted off the lip of the distributor? spark? DME? are the injectors plugged?

[rs-vic]

Your injectors may be stuck. Try tapping them with the handle of a screwdriver while running to get them going again. Happened to me with a 3.2 rebuild.

[ischmitz]

I think you have your priorities right. And check the simple things first:

You can exclude a couple of things already: The DME is working and the flywheel sensor is working. If not you would not even start the fuel pump or get any spark. Also if you dizzy is off a tooth I don't think any cylinder would fire.

Start with the simple things: Check the spark plug wires are all in the right position. Make sure the injectors are all connected. Next, you might want to pull a couple of injectors to verify they are really squirting fuel. Assuming you still use the Bosch Motronic and if you have access to a hammer (Bosch tester) you can actuate the injectors to make sure they fire.

After that it gets more involved. Cam timing but that is a long-shot IMHO. Keep us posted with updates.

Good luck,
Ingo

[BSF]

I double-checked all the plug wires and distributor clocking and confirmed everything was OK. I then fired it back up again and let it run a little longer and even revved it up a little to 1500rpm. I then felt the header tubes again and this time #3 came alive which means that the driver's bank was alive and the passenger's bank was dead. Looks like I'm going to have to remove the engine and re-time the passenger side camshaft. (It's 180 degrees out of position right now, I assume) Damn.

[hcoles]

cam being out 180 happened to me....I realigned in the car fired up and was fine

[BSF]

How did you realign the cam while the engine was in the car? Did you drop the engine enough to access the rocker cover and rocker arms to truly time the cam, or did you devise a clever way to rotate it exactly 180 degrees (from the front) without opening the rocker cavity?
Thanks

[hcoles]

losened the trans mounts and took out the rear mount bolts, lowered the engine some and started taking off the tin/etc. and then the "cam" cover, the hard oil line can get in the way, I managed to bend it out of the way just enough to get the cover off... your engine may be different.. then loosen the main cam nut and take out the pin. Be sure to get the cam in the correct location before you spin the crank, as I think you can mess up and have the valves hit the pistons while you are checking things before startup.

Someone help give a better sequence...or there must be a thread on this.

BSF - I suggest getting a better description of this - I think the Wayne book can be helpful, it has been awhile since I did this and may have forgotten something - I don't want you to damage your engine.

[briankeithsmith]

I think that's the main thing - valves hitting pistons. Loosen all rockers, but even that may not be enough.

Seems like you could turn the engine over by hand, and get the cam aligned 180 degrees the way you want it, then pull the cam bolt, and pin, and turn the engine to get it where you need it, then reinstall pin/bolt.

The hard part though is that in alot of cases, you can still end up with valves hitting the pistons... And also, its pretty hard to turn the engine over without the cam moving a little (if not alot) even though the pin and bolt isn't in place.

hcoles is right - double check the book!

Brian

[BSF]

Well, it was a 6 hour endeavor but I peeled off enough stuff to check the cam timing on the passenger side. Turns out that everything is OK. Re-checked the drivers side and it's OK too.

Current status:


1. Running with the idle switch disconnected seems to be working better. Engine starts and runs relatively smoothly if I set the idle setscrew to achieve at least 1000rpm

2. Timing at idle with the switch disconnected is 5deg BTDC

3. Cylinders 3 and 6 are still dead, but the other four are running well

4. Was getting 90psi fuel pressure at idle, dialed it down to 68psi (with the vacuum line hooked up) – wow, that FPR is hard to get to while installed!

5. Confirmed (with timing light) that all 6 cylinders are getting spark (at least at the wire, if not at the plug…)

6. Confirmed that the ECU is pulsing the injectors for cylinders 3 and 6.. hooked up spare (loose) injectors to those two wiring connectors, and I could feel the injectors “clicking”

7. Double-checked all the plug wire routings

8. Wideband O2 says 14.2 AFR at idle with # 3 and # 6 injectors disconnected, 13.7 AFR with the injectors hooked up

9. Can’t get cylinders 3 and 6 to fire, no matter what I do… (haven’t tried burning a chip yet to advance the timing further)

10. Confirmed that the two cylinders are dead in another way than feeling the header tubes… pulled the injector connectors one by one and there is no effect on 3 and 6, and it has a large effect on the other four.

11. Pulled the lower spark plugs for # 2, 3, and 6.

12. # 2 plug: looks like you would expect from 20 minutes of idling. Dry, black, and sooty except right where the spark is arcing

13. # 3 plug: light soot, you can tell it hasn’t been firing… but you can tell it fired at one point (remember when I was running on 1, 2, and 3?)… it was very slightly “wet” – glossy

14. # 6 plug: no signs of life. Has likely never seen fire. Can’t tell if it’s wet or not because it’s so clean.


Remaining options:



1. Plugs from # 3 and # 6 are just wet-fouled and need replacement (unlikely, but easy)

2. Cylinders # 3 and # 6 need more spark advance to bring them alive (unlikely, I tried revving the engine to 2000-3000 and it didn’t bring them alive, at least I don’t think so, but at that speed it’s hard to tell)

3. Interesting note: exhaust pops and shoots a small flame when I rev it up to 3000 and then close the throttle… would you consider that normal, or is it a product of being quite retarded on spark advance?

4. No compression on cylinders 3 and 6 (that would be bad)

5. Fuel injectors clogged on 3 and 6 (unlikely since I had them all professionally cleaned, but they are at the “ends” of the rails which is a common theme) – is it possible that they were damaged by too much fuel pressure?


Can anyone think of anything else???



Thanks,

-Brock

[JohnJL]

if you aleady have the plugs out you might as well check compression. That's easy...at least rule out something really bad...

[BSF]

Agreed. Does anyone know what compression should be (during cranking) for a 7.5:1 or 8:1 CR engine? (on a 3.6L with 964 cams)

Thanks

[JohnJL]

about 150? If the engine hasnt been broken in yet you may get low and quite varying results. You are really looking to see if you have at least 100psi to rule out compression as the culprit. If it hasnt been broken in yet you can get numbers all over the place.

[Candelaria]

If the compression is ok, check the fuel injectors if they are actually working, check those particular injectors if they are actually receiving a signal, if they are, tap on them with a solid item a few times, sometimes they get stuck because of inactivity.,Candy.