loftygoals

The injectors are firing. So I have fuel I have spark. Gotta be timing, right?

1) Brand new, but gap is unknown. I rounded the lock bolt trying to loosen it. My crude meassurements show that I'm pretty close. I'm trying to get a hold of a oscilloscope to test for sure.

2) swapped in a good working one from my 944 race car.

3) getting fuel pulses at the injectors. injector wiring tests good (had to rewire the 12V side.)

4) New. Getting spark, but I will swap the ones from the race car for good measure.

5) Checked and recheck. Then I checked again.

6) I have a meeting to run to, but I'm going to go through and check timing again. I just replaced the belt, so I was pretty sure about the timing. Is the flywheel marked at 180, too? I know I had the reference mark in the window and the mark on the cam in the right place. Still I'll check again.

-bj

n_hall

i had a no-start i count figure out. it ended up being the magnetic set screw on the flywheel had sheared off because of a bolt the i had unknowingly dropped in the inspection hole. i dont know how similar the manuals are to the autos, but it might be worth a look in the inspection hole.

loftygoals

If I'm getting spark it can't be the reference sensor can it? I thought the DME had to see the signal from the reference sensor before it would send a spark signal.

-bj

M758

I belive that is correct. the DME uses the speed & reference signal to tell the Coil to spark. Which plug sparks depends on the rotor position.

So it if it sparks then the DME is getting a rotating signal.


The thing to do may be to verify that you have the injector wired properly. I believe a 4 fire at once.

You could also throw starter fluid down in the intake (remove a vacuum line) to see if will fire. If so then you have spark a the right time and need to understand why you have no fuel.

Jay W

Are the spark plug wires in the correct place on the cap? You would have spark but if the wires are crossed...

PeteL

Is the DME from your race car interchangeable with the one in the 924? I don't know when/where the differences in the DMEs were, I know early and late are different.

loftygoals

Yes and no. To use an early DME in a late car, you have to swap AFMs as well. The injectors should really be swapped too. The early injectors flow a little less than the late setup, so if you run and early DME and late injectors the mix will be lean.

-bj

loftygoals

Yep, checked.


I assume you mean all 4. I remember reading that somewhere, too. When I tested the injectors while pulled from the intake, that's exactly what happened.

I did notice that injector #2 seems to be bad. It is leaking quite a bit of fuel. I'm going to replace it and see if it makes any difference.

-bj

M758

Ok,
So you have spark and fuel. However the car still wont start. it has to be timing related.

Did you double or triple check the plug wires? If they are not right the car won't run. The other thing to do is to pull the plugs and cap.

Then slowly turn the engine over. The rotor should turn such that as it approaches the #1 cyl (lower right) the #1 piston is going up. This should confirm you are on the compression stroke when the you are trying to fire #1. I don't think you can install the rotor in any thing other than the correct postition.

The only other thing could be if the injector wirring is fouled up so that it fires, but not at the right time.

loftygoals

Just checked the timing marks. They look damn near perfect. On the flywheel I checked both the upper and lower marks. On the crank the mark was right at the needle. I wish the timing was this perfect on the race car! I always seem to need a half of a tooth one way or another on it.


I'm thinking the problem is vapor lock. Injector 2 is leaking fuel bad. I just pulled the new plugs I installed. 1, 3, & 4 all were covered in carbon. 2 was soaked in fuel and still looks new. I think the injector is dumping so much fuel that it can't burn it fast enough. It is also probably keeping the motor from rotating as fast as it should to catch.

-bj

loftygoals

I swapped over the injectors from the race car. The car seemed to want to start. It was a lot happier, but still wouldn't run.

I looked back over the list of stuff--what hadn't I rechecked.

Then it dawned on me that I never did a compression check. The PO said they had done one and everything was fine. The guy seemed on the level, so I never checked it.

So I decided I better check:

140, 30, 140, 175

Hmmm..... Not good.

Then I remembered the old timing belt I pulled off looked brand new. Ah, now I'm getting it... I'm nearly 100% positive that the PO was a lying bastard. I'm nearly certain that the timing belt broke, they slapped a new belt on, and sold it when it wouldn't run.

Damnit!

I'm going to tear the thing a part to assess the damage.

-bj

carlege

Damn! i was wondering if you had compression. PO lied. This sucks but that woman will have a nice well put together car when it is done

Jay W

Was the low compression in the cylinder that had the leaking injector? All that extra raw fuel in the cylinder will make low compression numbers. Maybe not that low but lower than the others. Did you use oil in the cylinder to see if the compression comes up to make sure the rings are not the culprit?

loftygoals

Nope. I'm nearly positive that its a top end problem. Here's why:

1) The bottom ends on these cars are pretty stout, especially on an NA car. There lots of us spec racing with 150k miles or more on the bottom end with no problems. The only thing we do to keep the bottom end reliable is we replace the rod bearings. We might also drill another oil channel in the cranks, but a lot of us don't bother.

2) The compression numbers follow the firing order. Lowest to highest was 2,1,3,4 (well, 1 & 3 were about the same, but 2 and 4 were definitely on the ends.) If the timing belt breaks, the cam will continue to rotate because of inertia. The valve contact will happen in the firing order, but with less damage as the valve train slows down the cam.

3) The timing belt looked brand new. Why replace the belt on a non-running car? The most obvious reason is because the belt was broken. I'm betting good money that someone slapped a new belt on to see if it would still run after the belt broke.

I should know more for sure in a couple of hours. All I need to do is finish removing the headers and then the head will come off. I've never had to do a top end rebuild on one of these cars, but I'm amazed at how simple it is. I'm used to working on motors with separate intake and exhaust cams with variable timing. This thing is a piece of cake.

The irony is that I need to pull the head on my race car too. I have 2 valves get bent when 2 inner springs let go during a race. I guess practice makes perfect!

-bj

whalebird

A little info for referance. The referance sensor picks up top-dead center, but cannot do it just as the position dowel passes by it, it could be on the exhaust stroke, so the flywheel has to make two revolutions for the DME to get the referance. Thats why our cars turn two revolutions with the starter motor before the car starts. In my experiance, a busted T belt takes out the #4 exhaust valve more often than not - just my experience. A leak down test will tell you the story. Pump up the offending cylinders and listen for the leakage with a stethescope: leakage in the intake = intake valve, leakage in the exhaust = exhaust valve, leakage in the oil filler = rings.