Diagnosis ideas

[Travis944]

Hey folks,

I have a 1983 944 n/a that I can't get to start. I'm hoping you guys can give me some ideas on how to diagnose it. I've done some extensive reading/searching on here and can't find anyone who had a similar problem.

One morning I started it up to head to work. It started fine and ran for a few seconds, but then immediately quite running. No hesitation, stumble or anything. Just stopped. I thought that something had seized or maybe a belt broke so I didn't try to restart it and risk tagging valves.

After work, I pulled all the covers off to make sure the belt hadn't snapped. The belt looked fine, and I was able to turn the engine by hand so it didn't seem like anything was seized. I put it back together, and now it cranks but won't start.

I just replaced the battery, ignition coil, distributor, rotor, wires, and plugs hoping that would fix it, as it needed those parts anyway, but no luck. The fuel pump kicks on when I turn the key, and I cracked the nut at the end of the rail and I'm getting fuel to the rail. I have a good spare DME relay and tried swapping it out to no avail. I also have an extra air flow meter that I swapped but that didn't do the trick either.

Could it be a bad crank sensor or something? It seems like that's a common issue, but from what I've read I wouldn't get spark/fuel if that was bad.

Any suggestions would be greatly appreciated. Thank you for your time

[thekidd]

A bad speed and/or reference (crank) sensor would cause a no start. A way to possibly tell is if you get a tach bounce. If you don't, I'd try to take them out, see if metal shavings are on the bottom of the sensors, clean them if there is, and put them back in and try to start. If it doesn't buy new sensors. Don't mess with the sensor bracket. Sensors need to be at a gap of .8mm. Clark's garage has a write up on this whole procedure.

[Travis944]

Originally Posted by thekidd

A bad speed and/or reference (crank) sensor would cause a no start. A way to possibly tell is if you get a tach bounce. If you don't, I'd try to take them out, see if metal shavings are on the bottom of the sensors, clean them if there is, and put them back in and try to start. If it doesn't buy new sensors. Don't mess with the sensor bracket. Sensors need to be at a gap of .8mm. Clark's garage has a write up on this whole procedure.

I'll give that a shot, thanks!

[POPS 83 944]

I'm local to you, if you need some help just let me know.

[944tothefloor]

Oddly this can happen if your battery cables are loose and/or rusty. Not likely but an easy check.

[AA_Ezra]

Check for spark, then the injectors. Then post back the results

[pfarah]

Look for the infamous tach bounce while cranking over the engine. It should deflect 1/8" or so. If the original crank and speed sensors are there, it would be a great time to change them as well. Also try starting the engine with the DME cooling sensor disconnected (just under and to the left of the J-Boot.

[mattdavis11]

Check for tach bounce as mentioned above. I've had a similar situation. The first time I had a no start was when I cleaned the battery terminals. There are three small wires along with the starter cable at the positive terminal, one of the small ones was corroded pretty bad. I had to remove the wires from the lead terminal, cut the sheath back, strip the wiring, cut out the bad part, splice in new section of wire and replace the terminal connection with an aftermarket. I had no tach bounce.

I've had to replace two ignition switches. The first cracked, but the car would still run if the key was in a certain position after cranked, otherwise it would die. Going down the road, it would cut out, jiggle the key, and it would be back to life again. The next one wouldn't even crank the car when it failed.

The PO of my car did have problems with the speed and reference connections at the back of the motor, but they weren't replaced. They dried out and the connectors would no longer make contact. He just glued and taped them, I've since removed the tape and reinforced the connections with aquarium sealant so as not to have corrosion problems. Neither of the two go through the bracket anymore.

Hope this helps.

[pfarah]

Matt,

Why don't you replace the connectors? That sound like it may become a problem some day. Just saying...

[Travis944]

Originally Posted by POPS 83 944

I'm local to you, if you need some help just let me know.

Thank you kindly for the offer. I just may take you up on that

Originally Posted by 944tothefloor

Oddly this can happen if your battery cables are loose and/or rusty. Not likely but an easy check.

I just replaced the battery, and checked the cables and connectors at the same time. I doubled over everything and it all seems to be in good condition. Thanks for the suggestion

Originally Posted by AA_Ezra

Check for spark, then the injectors. Then post back the results

I haven't had an assistant to help check for spark, but I'll do that tonight. I just replaced the battery, coil, distributor, rotor, wires and plugs, so hopefully I have spark. I checked the injectors with a multimeter and am getting correct voltage readings according to Clark's garage. I also pulled the cap of the end of the fuel rail and I'm definitely getting fuel that far haha Thanks for the suggestion, and I'll post results of the spark check.

Originally Posted by pfarah

Look for the infamous tach bounce while cranking over the engine. It should deflect 1/8" or so. If the original crank and speed sensors are there, it would be a great time to change them as well. Also try starting the engine with the DME cooling sensor disconnected (just under and to the left of the J-Boot.

The tach does bounce while trying to start. Is that a definitive sign that the sensors are good, or could they still be bad?

I tried disconnecting the cooling sensor and starting, but had no luck. Thank you for the suggestion.

Originally Posted by mattdavis11

Check for tach bounce as mentioned above. I've had a similar situation. The first time I had a no start was when I cleaned the battery terminals. There are three small wires along with the starter cable at the positive terminal, one of the small ones was corroded pretty bad. I had to remove the wires from the lead terminal, cut the sheath back, strip the wiring, cut out the bad part, splice in new section of wire and replace the terminal connection with an aftermarket. I had no tach bounce.

I've had to replace two ignition switches. The first cracked, but the car would still run if the key was in a certain position after cranked, otherwise it would die. Going down the road, it would cut out, jiggle the key, and it would be back to life again. The next one wouldn't even crank the car when it failed.

The PO of my car did have problems with the speed and reference connections at the back of the motor, but they weren't replaced. They dried out and the connectors would no longer make contact. He just glued and taped them, I've since removed the tape and reinforced the connections with aquarium sealant so as not to have corrosion problems. Neither of the two go through the bracket anymore.

Hope this helps.

I haven't checked the length of the wires to the starter, but I have had to replace the starter multiple times. I blipped the key while in gear and the starter is engaging. If the ignition switch is bad, would it allow the car to crank at all?

I'll double check the connectors at the top for the sensor, there is some electrical tape on there so maybe the PO had a problem with them in the past. Thanks so much for the suggestion!

[wrench1]

Travis,
If you have fuel, spark and tach bounce you are doing well.
I offer this, as it was what was wrong with my son’s car, try the ignition switch.
We would lose power intermittently and spark.
The early ignition switches are known to crack and go bad after 27-30 years.
These are cheap to purchase, around $25 or less.
Don’t buy the China knock offs, not good quality.

I hope it’s not the DME.

[pfarah]

Travis,

If it bounces, then you're ok however; I would still replace them if they are original equipment. Less to worry about the inevitable.

[Travis944]

Originally Posted by wrench1

Travis,
If you have fuel, spark and tach bounce you are doing well.
I offer this, as it was what was wrong with my son’s car, try the ignition switch.
We would lose power intermittently and spark.
The early ignition switches are known to crack and go bad after 27-30 years.
These are cheap to purchase, around $25 or less.
Don’t buy the China knock offs, not good quality.

I hope it’s not the DME.

I'll definitely look into that as well. Thanks so much for the help and the tip.

Originally Posted by pfarah

Travis,

If it bounces, then you're ok however; I would still replace them if they are original equipment. Less to worry about the inevitable.

Good call, I'll have to add it to the to-do list ( towards the top of course). Thanks again for the help!

[mattdavis11]

Originally Posted by pfarah

Matt,

Why don't you replace the connectors? That sound like it may become a problem some day. Just saying...

I figured if they've been working just fine for 15 years the way they are, why mess with them.

[Ky914Newbie]

I don't see it mentioned yet. Have you checked the rotor inside the distributor to make sure the set screw hasn't backed out?

[88Silver924S]

May we assume you have checked your fuses for a blown fuse?

[Travis944]

Hey folks, I think I have good news!

So it turns out that even after replacing the battery, coil, distributor, rotor, plugs and wires, I'm not getting spark after all. After swapping my good spare DME with no luck, I decided to check the ignition switch as per a suggestion by wrench1 and mattdavis11. It turns out it is cracked, albeit not as badly as some of the pictures I've seen. Do you blokes recon this could be the cause of my problem, even though its not cracked that badly? Is there a way to bypass the switch and see if it still won't start?

Originally Posted by Ky914Newbie

I don't see it mentioned yet. Have you checked the rotor inside the distributor to make sure the set screw hasn't backed out?

I just replaced the distributor and rotor, but I reckon its possible it's backed out since then. I'll double check, and post results. Thanks for the suggestion!

Originally Posted by 88Silver924S

May we assume you have checked your fuses for a blown fuse?

Yes sir, that was the first thing I checked. I'm sorry I didn't mention that in my original post. Thank you for the suggestion!

[Travis944]

Alright lads, I have replaced the broken ignition switch, but still get no spark. I'm about to tear my hair out...

[mhariush]

Maybe go over all the ground wires and make sure they're clean. I had starting issues on my old NA. The heater control valve leaked and was dripping down on the grounds. They were corroded and caused issues.

If the heater valve is near the firewall at the back of the engine on the early models, that's def worth checking. And check the rest of the grounds too.

[Travis944]

Originally Posted by mhariush

Maybe go over all the ground wires and make sure they're clean. I had starting issues on my old NA. The heater control valve leaked and was dripping down on the grounds. They were corroded and caused issues.

If the heater valve is near the firewall at the back of the engine on the early models, that's def worth checking. And check the rest of the grounds too.

Thanks, will do