911 SC K Jetronic engine wont even fire up

[haveacamper]

ok guys....i started a thread a while back about my 911 engine cutting out during warm up.

to refresh peoples memory its an 1981/1982 SC 911 engine in a vw campervan.

unfortunately i never got the engine running and i'm still trying. i now ave a bigger issue...the engine wont even fire up. i will explain what i have checked and see what you think.

i have removed all rigid lines form the injectors and bleed about 100ml of petrol through the system. then i removed the injectors and tested them all. the spray pattern is consistent and accurate to the haynes manual. i have checked the spark and is a little weak. the dissy cap, rotor arm, leads are good as new. the spark plugs are brand new. first off i dont understand why if i have fuel and even a weaker than normal spark the engien should at least fire up and run rough.

i have chekced voltage of the battery - also brand new - and this is 12.5V. i have checked the resistance between 1 and 15 on the coil and is 0.5ohms (haynes says it should be between 0.4 and 0.6ohms. i have also checked the resistance with terminal 4 (HT lead) which is also in the middle of the range given in Haynes.

With all of the ignition components in good condition and within the tollerance stated in Haynes i am unclear as to the issue with the spark.

the CDS unit (ignition unit) does whislter with ignition on so appears to be in working order.

also, with the air box filter removed, it is possible to feel the plate being sucked up during cranking - telling me that there is no airleaks/substantial air leaks. also, fuel should be getting to the cylinders during cranking.

you assistance would be very much appreciated. are there are tests for testing the CDS unit further? its an expensive component to replace if misdiagnosed.

thanks in advance!

NaFe

[Targalid]

Assuming you have fuel, then it must be ignition. Is the timing correct? Are the points gapped properly. The spark should not be weak with CDI. Even though the plugs are new they can be fouled quickly and will not fire if wet. I have had new plugs fouled more times than I care to admit. Take them all out and dry each one with a torch and then check each one to see that it is firing. Turning the motor over with the plugs out will dry the cylinders if you are flooded.

[Bob Kontak]

I did not read where you checked the injectors for fuel when you are turning the engine over. Vacuum will lift the sensor plate but that does not mean that fuel is flowing.

In my 81 SC the fuel distributor will make a screeching noise with the key turned to on (not start) and with my hand lifting up on the sensor plate. Can you do this?

Keep the info coming. We will get it going.

[haveacamper]

Bob, correct me if I mis understand u, when I lift the plate up there is a screeching sound or sorts. I thought this was coming from the fuel pump, but it could be coming from the fuel distributor.

Thnking about it, when I pulled the injectors to test fuel I did not actually crank the engine. The way I tested fuel was coming through was to put ignition to on (not cranking) and push the plate up. However, what I did do when cranking I did try to manually push the plate up a little, but this didn't do anything

NaFe

[James Brown]

Ok now check the fuel pressure or the fuel pump. If you have fuel pressure when you lift the plate, fuel should come out the injectors. Pull one out and, still connected, place in a glass container and check if you get fuel. Try that next

[haveacamper]

I will try this, but just so I can understand the system better, what's the difference to pulling one out and pulling them all out to test fuel during cranking - except only having to pull 1 injector

[Walter_Middie]

You can do the fuel check with one out, or them all out - same result.

You mentioned above that you did lift the air flow plate with the ignition on, but you didn't tell us what happened. Did fuel come out?

[haveacamper]

Walter, I lifted the air plate up with the rigid fuel lines disconnected from the injectors and pump a load of fuel through - all lines consistent. I then attached all 6 injectors and put them into clear pots and all the injectors sprayed consistently with eachother.

I will try cranking the engine with one injector out to see what happens. I still can't help but think the spark it quite weak

[Walter_Middie]

It sounds like you are getting fuel - so I would suspect no spark.

[Walter_Middie]

What kind of ignition system do you have? The 3.0L engine usually has a 6-pin CDI box. You can check for spark by grounding a plug and cranking the engine. Don't hold the plug in your hand as you will get jolted.

[haveacamper]

Yes I have the 6 pin box. As per the first message, I've inspected the spark. I have done what u said using the central HT lead and the individual spark plug lead. I have also inspected the spark at the sparkplug. It appears to be weaker than I'd expect, but I have no reference

[Walter_Middie]

What's your battery voltage while cranking?

If your cold start valve is not supplying extra fuel during cranking, these engines can be very hard to start. If you breifly lift the air flow plate with the ignition on, then crank the engine, does it fire at all? Does it sound like it might start? Or is it just cranking.

[Bob Kontak]

I wrote this while others were typing:
Yes - sounds like you have fuel. The screeching has to come from the fuel distributor area. IT may be the pintles on the injectors, I don't know for sure. If it was that loud when you are standing at the rear of the engine AND came from the fuel pump the neighbors would call the po-po. Making this statement based on where the fuel pump is on a 911.

How easy is it to get to the cold start injector to pull out and test? Your cold start valve should fog the air box to give you a cold start then die instantly if you have a fuel delivery problem to the injectors. If there is a huge vacuum leak it starts dies and backfires loudly through the airbox - from what I have seen - this is when the injectors are delivering fuel.

You mentioned in post #4 you lifted the sensor while cranking and it did not do anything. I would try James suggestion in post #5 but put the glass under one injector while cranking. You ought to get fuel. I would definitely do this first.

Then check timing if you have fuel - could the distributor have been put in backwards after you had the cutting out while warming up issue? DOuble check that.

Then check the cold start valve.

Also, did you find the cutting out cause from your original post?

Do you have the correct fuel pump? The SC runs at over 70 psi system pressure.

[pete3799]

Plug wires on correctly? Dist. turns counter clockwise.

[James Brown]

Your doing good NaFe, were just going through the standard troubleshooting procedures for non starting. After the basics (fuel spark air) we will start checking fuel pressure in the CIS system so if you don't have a fuel tester and a timing light, get one, there not that expensive, if you don't need the best quality. Other tools you need is vacuum finder spray (starting fluid). Read the CIS primer web site and get a copy of Bosch's theory of CIS operation manual to understand how and why this system works and why adjusting one component will effect others. Hand in there!

P.S. I have a new fuel pressure tester set for sale, $50.00 + shipping.

[haveacamper]

i have replaced the cold start valve already. i know this works as after cranking, if i take the plenum chamber off (connecting the air plat to throttle body) and look past the butterfly valve the chamber is wet. also if i put a rag down there i can soak up the fuel thats come out of the cold start valve.

bob, i dont have know the definitive issue of the original cutting out, but believe it to be a kinked air hose that bypasses the throttle body.

as for fuel pump, i dont know if its the correct one, but its the one that came with the engine and - i saw the engine running and went for spin in the previous bus that the engine was installed on.

again, the engine has run, albeit a a short time befopre cutting out before now. i will be cranking the engine with one injector removed tomorrow.

pete3799, the wires are in the correct order, the engine has run before and i have double checked this. the engine should at least fire up, but doesnt even sound like its anywhere near firing up.

BIZARRE!

James, would you find out how long and how much it would be to post it to me in the UK? camt seem to find a CIS specific tester on initial looking.

it has to be something stupid!

NaFe

[James Brown]

Ill check for you, like you said it's something stupid.

[haveacamper]

ok guys, i'm going down to work on the engine this evening.

the plan is to check that i am getting fuel through the injectors during cranking by removing one of the injectors. the battery is on trickle charge to make sure its good. if I dont get fuel what could this be - apart from wiring fuel pump relay incorrectly?

is there any method for checking whether my CDS ignition unit is good? i am still convinced the spark is not good. the rotor arm, dizzy cap, leads, plugs look in good condition and I have chekced the coil's resistance inline with Haynes.

does anyone know the exact time and temperature settings of the thermo time switch connected to the cold start valve?

NaFe

[Targalid]

One more stupid thing to check. Is the ground strap properly connected? Weak ground will give good voltage readings but lousy current flow.

[haveacamper]

i think its good, but i will check this too this evening