originalmotorhead

Just did a search and came up with lots of things to check tomorrow, but decided I would "vent" and post my problem tonight anyways.

Found this link that seems rather helpful on things to check for early cars: https://rennlist.com/forums/924-931-...t-i-fried.html


My scenario:

I replaced timing/balance belts on sunday. I fired car up after the job and it ran good. put it away for the night. Tonight, monday, i took exhaust header off, welded a new 3 bolt flange on it and fabbed up a header back exhaust.(pretty much a complete exhaust) Now when i go to start the car, i get no wiggle of tach needle, no spark at #1 cyl(i connected a plug light to #1) and i changed coils and dme and no difference. Guess I need to test for voltage at the coil.

I'm totally baffled because i didn't monkey with anything electrical under the hood since yesterday when I ran the car for first time since belts were replaced. I have a battery cut off switch so the car was completely dead when I went to tack weld the flange onto the header and the other pieces of the exhaust too.

Ideas? tomorrow night I will try another dme relay for grins, check coil voltage before dist cap.. Car really irks me some days, ok, many days. hehe


Tom

xupkid2

Check the reference sensor connections. You could have wiggled them loose when messing with the headers. No tach bounce usually means reference sensors and if reference sensors arent right the ignition timing is messed up.

luftpirate

Reference/Speed sensor, try cleaning the contacts on the connectors right in front of the firewall with brake cleaner and reseat them a few times. My connectors were brittle and practically disintegrated, this problem has accounted for 1 of my 3 (no start, no tach bounce) issues.

peanut

There are some Bosch Motronic troubleshooting guides on the net which are very useful for giving an insight into the working of the fuel and ignition system .

The ECU needs to 'see' 200+ rpm from the crank sensor before it grounds the DME relay which in turn supplies both the fuel pump and the ignition system and fuel injectors.

if you remove the DME relay and substitute a 3x way bypass cable with spade connectors (as detailed on Clarks Garage and on here), it will bypass the ECU and DME and should activate the fuel pump and ignition system.

That way if it then doesn't start or try to start you have eliminated a lot of componants and narrowed the problem down to the crank speed sensor or the constant power supply to terminal 30 on the relay socket.

originalmotorhead

I did try reseating the ref and speed sense plugs once or twice last night, even though I had not touchched them since the car was running the day before. But I'll try that again tonight and use air or cleaner on the contacts.

Last night I also swapped the coil and the ecu and there was no difference in symptoms/lack of start. I didn't pop a plug out to see if there was fuel but there was positively no spark. Will check for fuel tonight too.

Will also look up the 3 way dme bypass, and or swap dme relays too.

i didn't see any blown fuses but will wiggle em tonight or look at the back of the fuse panel.

Some days this car is just plain frustraiting.

thanks for the input guys !
Tom

peanut

do a search for 'no start ' etc on this forum. This subject has been covered comprehensively in the past few weeks.

You need to appreciate that your ignition system coil is controlled by the ECU . There will be no high tension from the coil or spark until the ECU is satisfied by the various sensor imputs .

You should make sure there is at least 4 galls in the tank then use the 3x way DME bypass to run the pump and check fuel pressure and fuel flow.

You can also check to see if you have a 12v+ supply at the injector electrical connectors.

All this is covered in previous threads and its pointless going over it again .
Use Clarks garage Workshop articles and follow there trouble-shooting guides in correct sequence otherwise your random poking and prodding is just going to create more problems

originalmotorhead

ok, just went thru the clarks garage FUEL-16 checklist and everything is in order up to the ref/speed sensor part. going back out to monkey with those items but everything else checks.

my thought seriously is that its the ref/speed because i do not get any spark signal. if i jumper the coil, i get spark, if i test the coil leads i get +12 at the one side. i even tried a spark tester from coil to ground but it only lights up if I actuate it with wire to ground on neg side.. so dme is not sending spark signal.

if i jumper dme, then i get fuel pump running.

ugh. here little ref senser, here boy

Tom

Bri Bro

Sounds like something got zapped when you were welding. I am betting the cutoff switch cut the positive lead, not the ground. Not sure were you attached the ground lead of the welder, but if it was to chassis when welding on the headers, you could get some large current through the engines grounds. Are you sure the DME you swapped in works?

944Ross

+1 MIG or TIG?

originalmotorhead

MIG

i found the problem(I do believe). it's the Speed sensor. well, if it was not bad before, it is definatly bad now because I broke it trying to remove it. the sucker was corroded in like a mother.

the ref sensor checked out as 1k ohms even though the wire seems loose where it goes into the actual sensor. but speed sensor read nothing so I wiggled the **** out of the lead wire and still got nothing on the meter.

luckily I have a second set of the sensors from an old parts car. gonna swap one out maybe tomorrow night. both checked little over 1k ohms so they are good.

bummer is now I have to set the depth of the darn things cause I removed the whole sensor holder thingy. thems the brakes. i guess..

For the life of me i just do not understand why the speed sensor would take a **** out of the blue. darn natzi parts ;p

i honestly do not believe the welding had anything to do with it. i've welded on the car before and obviously it has to be grounded to get current to do the weld. i had the ground attached to the header and not the body so the current source was local and not thru the chassis via the motor to body cables.

I'm curious, can these sensors be sourced / bought new?
both are same part number: 0261210003

Tom

Bri Bro

Glad to hear you didn't have a DME issue. Paragon has a replacement at 1/3 the cost. It has a slightly longer lead that needs to be tucked up into the harness. Other then that, a direct replacement.

http://www.paragon-products.com/Prod...0.002&CartID=1

peanut

parts of the ECU work on less than 1+ volt .......I hope you disconnected the battery and ECU before welding .

I have never heard of a faulty sensor. It is only a magnet so nothing to go wrong with it really unless the bracket comes loose. Its always the wiring and connectors that have the faults. Make sure you tape up any holes in the clutch housing before you work on the sensors as a stray bolt falling into the housing is sure going to spoil your day

originalmotorhead

I have a battery disconnect switch so that removes the positive lead from the whole car.

Regarding the sensor going bad. I sprayed the connectors down with brake cleaner and wiggled the **** out of the wires and even banged the connector itself on the manifold and every time I got the same reading from my multimeter, an infinite reading.(I used two different multi meters to be certain) that was on the speed sensor. ref sensor checked in at 1018 ohms every time. I didn't dig out my o scope since I got an open reading. My spare 2 ref/speed sensors from my parts car both check in at 1020ish ohms too. But I'm thinking why not install new and then no worries for a while, right?

I have 3 DME's so I feel fairly confident it's not a computer issue seeing as only 1 was installed while i was welding the exhaust.

I'm headed to the stoddard swap meet this saturday so I'll wait and see if I find any new ref sensors there. Tonght I'll just use my spare ones just to make sure i've found the gremlin. (thanks for the link Brian)

Boy I was nervious yanking that fuse panel out but i got a good look at the wires behind it and it's in fair condition so for now I'll leave be. Was evidence of some hot wires but the dme related wires looked intact. Wondering if it would be worth the effort to take the dme relay socket off the main block and snake the wires out and around to an easier to access location. hmm

Tom

peanut

what you could do is find any relay with identical spade connector arrangement .
Remove the entire internals.
Solder a piece of decent sized wire between terminals 30 & 87 and 87b inside the relay .
Solder a 1x way switch between terminal 30 and the other two terminals and fit the switch into the relay cover.
Stick the relay in place of your DME relay. Switch the switch on for running and simply switch it off again when you get to your destination.
That way you bypass both the DME relay and the ECU
Heres one that I made using an old Mondeo flasher relay . Instead of soldering a direct wire link like mine you could run a cable out to a switch for easy acess to switch it off

If the car won't run with the DME relays bypased then you have another issue.

originalmotorhead

That sounds like a good idea for a backup / spare in the glovebox/toolbox.

Tonight I plan to put my other ref sensors in. Hopefully get them set with the propper clearence on the flywheel.


Heck, it might be a good idea to perminantly mount a switch in the dash since this is a race car / track car only and i want to eliminate the ignition key at some point anyways and have just a toggle and push button for starter. I've already ground out the steering column lock so nothing holding back there.

Tom