3.2 Rebuild first start question

[wjdunham]

I have a freshly rebuilt 3.2 up on a stand and trying to get it fired up. It's not catching and I have a few questions to help guide my debug.

What I do know:
Getting oil pressure without plugs installed - starter will at least crank the motor with no plugs
ECU is good - tested in another car
Getting fuel pressure and 12V on the injector harness
Injectors were re-built
I think I'm getting spark - having some issues with the starter so can't crank for long with the plugs installed but for now let's assume I'm getting spark - did see a flash from my timing light at least
Speed and reference sensors are new - If I'm getting spark would mean that these are being read properly

What I don't know:
CHT sensor is used and not 100% sure it's good - this shouldn't prevent starting even if bad?
ICV is used and not 100% sure it's good - shouldn't prevent starting? will affect idle once fired?
AFM is used an not 100% sure it's good - shouldn't prevent starting? more of an issue when motor is under load?
O2 sensor is disconnected


I have a NOID light on the way to check if the injectors are firing.
I will also get some starting fluid spray and give that a try.
I need to triple check that my distributor is not 180 degrees off

Are my assumptions about the AFM, ICV, CHT etc... valid?
Beyond the above debug items, what else should I be checking. I'm hoping to not have to start swapping parts unnecessarily until I at least get the thing to fire and see if it will hold idle and respond to the throttle.

Thanks for any help

Bill

[megerian]

CHT when disconnected or giving a bad reading will indeed prevent starting - I believe you can jumper it to check

[wjdunham]

Originally Posted by megerian

CHT when disconnected or giving a bad reading will indeed prevent starting - I believe you can jumper it to check

Thanks. You mean disconnect the CHT and jumper the harness to the DME? Would I just jumper with a wire or do I need a resistor of a particular value?

[Flat6pac]

You may have your flywheel sensors reversed
Unplug and swap location. If you get it running I use fingernail polish on one set of black connections so I don’t get mixed up again
Bruce

[megerian]

I have heard of people jumpering the CHT with a paper clip - the reason I know that the CHT will prevent the car from starting is that once mine became dislodged while driving, and the car died immediately and would not restart.

[proporsche]

any reason you do not put the engine in the car? ..i personally like when i rebuild engines,i`d go straight for driving,not sitting on test bench.It take some procedure to break it in..and the testing bench will not do any good to it.

Ivan

[wjdunham]

Originally Posted by proporsche

any reason you do not put the engine in the car? ..i personally like when i rebuild engines,i`d go straight for driving,not sitting on test bench.It take some procedure to break it in..and the testing bench will not do any good to it.

Ivan

I was only going to do the first 20 minutes at 2000RPM on the bench. I will not have the car back until late this year or early next and want to have the engine ready to drop in. It's a lot easier to debug things like the reference sensors if the engine is not in the car. Maybe after I confirm that it fires I will just wait and install in the car, but want to make sure I don't have to tear it down first :-)

[proporsche]

well i would wait until is in the car-because you cannot duplicate the load...seams like there is no rush so why rush it;-)..trust your work a little more;-))
Ivan

[boyt911sc]

Originally Posted by proporsche

well i would wait until is in the car-because you cannot duplicate the load...seams like there is no rush so why rush it;-)..trust your work a little more;-))
Ivan

Ivan,

You missed the objective of the OP. He wants to make sure that the engine is running before installing it back in his car. What is wrong with that? I never install a motor in the car without verifying it would start and idle. Unless you don’t have an engine test stand, then you install the motor directly back in the car.

How could you test the LOAD if the motor does not even starts at all? For example, what if the CSV is not working? You know well how difficult to access the CSV with the motor installed. And this is just one example and could give you more. Wait till you work with CIS motors.

Tony

[proporsche]

Tony ok i got it....in my case i did not have to ever worry about the engine not starting after i rebuild it.....i do really mean never.Once you do it it will run.i can imagine somebody, who does not do the engine job often, would like to know if everything is fine;-)
make sense......
WJ....no offence mented;-)))))


Ivan

PS..ok never?..... yes it has happened to me in my 1st engine back in 1985 on my own 911, i did not set the Z1 and i bend valves on 2 3 cylinder.At 5p.m i started the engine happy it ran but only in 4 cyl so i took the engine out put it in the stand and took that side apart..replaced the bend valves and about 1.a.m. next morning the engine started again a purr like kitten so never ever is not true;-))))after this all my rebuilds were perfect;-)

[wjdunham]

Whether the engine is in the car or not - I'd still like to understand beyond the CHT what else I might be checking.
Thanks!

[Klax]

I just fired my 3.2 rebuild for the first time this week and the issue I had at first was that multiple injectors were not firing. This was despite the injectors being professionally refurbed and tested a month and a half prior. I read, on here, about using a 9 volt battery to give them some pulses until you can clearly hear an audible click of the injector opening/closing

[proporsche]

Bill.....
. so the basics, do you confirm you have fuel and spark??

Ivan

[wjdunham]

Originally Posted by proporsche

Bill.....
. so the basics, do you confirm you have fuel and spark??

Ivan

Not yet - I need to get the engine on a proper stand with my transmission mounted so I can reliably crank the starter, may be a few weeks before I get it all hooked up again.

[proporsche]

Bill,looks like a lot work just to get it started.The engine was running before the work, correct?
So if yes why (i know why;-) ) to go through all this trouble..the cam timing is correct .You did not pinches any piston rings,you had the valve job done by pro, used correct rod and main bearings....if yes to all of this.....the engine will run when in the car;-)))))))))
I would rather enjoy the late somer you have there then being in the garage;-)hopefully the fires are away from your area??

Ivan

[wjdunham]

The motor was completely disassembled when I bought it, so it was a complete, top to bottom rebuild:
Cylinders bored to 3.4L and re-plated, new JE pistons, ARP rod bolts, 964 cam grind, enlarged throttle body, SW chip, SSI headers. Heads, rockers, crank, rods all serviced, re-bushed and in like-new condition now. Cam timing, deck height, etc... all triple checked and the motor turns over fine without spark plugs installed and builds oil pressure well. Don't see any oil leaks so far with oil sitting the case at least. I seem to have good compression, when I install the plugs and try to crank it over the fixture that attaches the start to the motor is flexing and the starter gear won't engage the ring gear properly which is why I am where I am now. I need to build a new stand, attach my 915 and try again to get it cranking. We got it to crank long enough for me to see the timing light flash a few times which is why I believe I have spark. Cannot getting going further so I can check if the injectors are firing.

So, I believe all the mechanical pieces are fine. A 3.2 top end has all sorts of sensors and electronics that came with the motor that I am only partly able to test and ensure are functioning properly.

Bill

[gomezoneill]

I've rebuilt dozens of 911 motors from the 1970's on. Never have I put one on a stand to test. Just put the thing in the car and start it.

[wjdunham]

Originally Posted by gomezoneill

I've rebuilt dozens of 911 motors from the 1970's on. Never have I put one on a stand to test. Just put the thing in the car and start it.

I would be more inclined to do so if I actually had the car in my garage :-) It's currently with my body/paint shop and I won't have it back until the end of the year.
Bill

[wjdunham]

Update - turns out my issue was indeed a bad CHT sensor. Measured open circuit with my Ohm Meter which was causing an overly rich mixture. I could see this on the plugs when I pulled one. I guess this in combination with the fact that the engine was brand new build prevented it from starting at all. I figured a bad CHT would cause it to run pooly but should still start so I didn't really suspect that as the main issue. Everything else checked out fine, so lesson learned here. I jumpered at the connector with 270 Ohm resistor and it fired right up.

Ran the motor for the 20 minute 2000 RPM break in and I think I'm glad I ran it on a stand vs. in the car. I had one small oil leak from the intermediate shaft cover plate which would have been a pain in the ass to get to with the motor on the car. Otherwise dry as a bone so overall I'm very happy as this is my first complete engine assembly.

[Rodsrsr]

Originally Posted by gomezoneill

I've rebuilt dozens of 911 motors from the 1970's on. Never have I put one on a stand to test. Just put the thing in the car and start it.

This^^^^If rebuilt correctly, there's nothing mechanical that would prevent it from starting. Any electrical issues could easily be tackled with the motor in the car. Its literally 4 bolts to install these things.