78 starting issues
 

I recently bought a 78 928 that had been sitting in a garage for six years. this is the first Porsche I've worked on and I've learned that they didn't engineer these things for easy maintenance. I've replaced the timing belt and had to redo the hole fuel system. I've got fuel through the injectors, spark, and compression. But it still doesn't even try to fire. I've installed new spark plugs and wires and have plenty of spark. I'm 99% sure that I timed the cam's correctly. I also took out an injector to ensure fuel flow and discovered that it injects at a continuous rate and doesn't pulsate. This really confused me because it looks like it has a fuel distributor under the air filter. So I'm not sure what the injectors are suppose to be doing. Maybe it only continuously injects when starting the engine. I'm not sure. like i said, i have no experience with these awesome foreign cars so i would GREATLYYYYY appreciate it if someone could give me a few pointers. Thanks

78/79 and Euro up to 83 are CIS, continuous injection system. Fuel flow is determined by the difference between manifold pressure and fuel injection line pressure. The line pressure is set by the thing under the air filter and the pressure as regulated from the pump. For troubleshooting you will need a fuel pressure gauge.

RE fuel, spark, and compression, eh one of them ya don't got.

If your SURE about spark, and spark timing, I would try a VERY small shot of starting fluid down the air filter throat. If it doesn't kick over even a little, my guess is your totally flooded with too much fuel or compression isn't there.

Been there and done that. Had to replace my entire injection system on my 79 and it is a bear to start once things are back in....
What I did was I:
1) Cranked the engine a couple of times to build pressure and then gently pressed on the CIS plate (round under the air filter) to the bottom as far as it will go .. gently. This opens the fuel to the injectors so you know that you have fuel to the injectors. Did this about 2-3 times.
2) then it sputtered a couple of times.
3) then I had to put about a thimble of fuel onto the cis plate. This gave the engine enough fuel to start engine vacuume and get the process going. Unfortunately this was a fire risk so if you elect to try this... BE CAREFUL. other option is starter fluid..
Having put new injectors and a CIS distributor I can say it is a pain to get it back to where it was.

Good Luck!

Curt

Curt,

Is this what you have to do on CIS systems once you change them out? I am also having a hard time starting mine.

I would troubleshoot just like I would electrical;

Check the battery voltage, check the fuel pump output pressure.
Check the voltage at the fuse panel, check the pressure at the fuel pressure regulators.
Check the voltage at the light bulb, check the pressure at the fuel injector.

All this time I would have a vacuum gauge on the manifold, and also check the vacuum lines for vacuum and no leaks.

When you turn the key, you should hear the fuel pump start. Like said above, just gently push down on the Air plate until you have purged the lines of air. You should then be able to start things up. Depending on how much fuel you flow out while purging, you may have to wait a bit or it will act like it's flooded.

If you have fuel, spark and timing is right it should start. When you changed the timing belt, how did you ensure the cam gears were in line with TDC on the crank? If you are off a couple teeth, it will not start. Also you may have the distributor off a tooth as well.

The car was a engine seize. I replaced the engine and while the engine was out, I did the TB. TB was aligned according to the WSM. Cam Gears lined up to marks and crank at TDC. I even made sure the Piston 1 was at top when I put the Distributor on and made sure when the Rotor came around when dropping in, it was pointing to Cylinder 1. I never did purge as said like above. I do have the key on as I jump it from the front of the car (harness). Do I need someone in the car pumping on the gas pedal?

When I went through all the usual things... fuel pump working, ignition working etc. etc. I found that I had to "prime" the system. Lifted the cis distributor a few times to ensure that fuel was going to where it had to go.. Not sure why but had to fiddle with it once I changed out the fuel distributor.. Hope it all works out. Definitely try what the guys are recommending... My car is of course.. special. :-)

Ok, verified Plug Wires going to the right cylinders. Put at TDC, marks on cam gears align with marks. Pulled plug 1 to make sure it was at the top. Cylinder 1 was a top. Pulled Distributor Cap and rotor seemd 1 gear off clockwise. Pulled distributor and move 1 gear counter clock. cranked engine and then pushed plate slowly down, crank and nothing. sprayed a little bit of starter fluid and crank and nothing. Measured voltage at battery (11 volts) and 1 volt at coil. Hooked up the battery on a 2 amp trickle for an overnight charge. Will try again tomorrow after work.

that's why it's called CIS (continuous injection system)

the fuel distributor distributes the fuel to all cylinders evenly (or, at least it's supposed to), as opposed to a single fuel rail running to a string of injectors.

the CIS injector will "buzz" when operating properly. it does not "inject" each time the piston comes around on the intake cycle like an electronic injector does, it injects constantly.


--Russ

did you verify spark at the spark plug----regardless of timing...?

(take a plug out and turn the engine over while grounding the plug's ground electrode)

If so, then move on to fuel diagnosis......



--Russ

I don't know if this is a stupid question or not, but does it make a difference if the TDC is exhaust or compression stroke? I mean is that something that could be wrong?

Hi Russ,

Yes, Over the weekend I pulled plug 2 and grounded it against the hoist eye and cranked over and got spark.

OK so things that we do know:

Looks like timing is OK
Getting spark OK
Air.. well its getting to the cylinders.

Fuel: hmm sounds like its not quite there yet. What I would try.. (if not done yet)
1) crack open the fuel lines on the fuel distributor. That way you know that fuel is getting to the lines..
2) press on the fuel distributor a couple of times to ensure that fuel is flowing to the injectors. perhaps pull one to ensure is flowing into the intake manifold.
3) Then shoudl get some sputtering.. I found that it took a coupel of cranks before it would run reliably and the engine would supply enough vacume to pull down the fuel distributor and keep things going.

It was a pain to get things going again.. :-( But it will start running again. :-) And then the fun begins with adjusting the mixture!

All the Best,

Curt

I had a wet plug so it must be going through the injector (or at least 1 or them).

I don't think the fuel distributor works off vacuum, its flow over the plate thing that moves the arm down like in the barn door air meter with the L jet.

If the plugs are wet though, thats fuel enough, maybe too much.

Is your cold start injector firing?

there are no stupid questions............




it does make a difference---

easiest way to find TDC on the spark stroke is to pull the spark plug, put your finger over the plug hole, bump the motor until the engine blows your finger off the hole, and then you've got the firing stroke. Check the distributor rotor to see which plug cable it's pointing to, and align the cap to the rotor.

once the engine is started (it probably won't run very good, as the timing will be off), you can then time the engine properly.


I know this is an old school way of do it, but it's quick and you don't have to rely on timing marks on the harmonic dampener that may be correct or not.


--Russ

I am not even sure what this is, so I am not if it is or not.

on the front of your intake plenum (that's what the intake tubes are connected to), there is an injector with a fuel line connected to it.

this is the cold start injector.

--Russ