Thank you for viewing this post. Having driven and repaired Volvos exclusively since 1978 I'm reached a point w/ my current ride where I know the problem - No Spark - but I can't figure out what is causing (or preventing) my ignition system to spark from the coil/primary wire. This post is a long post but in order to obtain advice the more information the better the advice and wow, do I need advice!!


The CAR:
1994 850na, manual trans, 250K+ miles wagon, I’m second owner, always serviced from new
it was running fine, no intermittants, good mileage, etc. Good, good, good.

I also own a 93 850 that runs, (important as it became a “swap parts” car) except for a bad water pump. This 850 was starting and running on the day problem arose.

I was setting up to replace the water pump on the 93 Volvo 850 (the one that starts and runs) when:my Wife backed out of her garage and bumped the front end of the 94 wagon. No big deal as there was no minor scrapes but not even a cracked grill.

Is there an electrical or other coonection near front grill that could have been cut, crimped or otherwise broken?

But now the 94’ 850 wagon won’t start. It apparantly has No Spark. To test this I replaced the primary coil lead w/ a spark plug and wire to ground. I also tried grounding the primary coil w/ just a speaker wire #14 but in each case - No Spark. I’ve repeated this test each time as “repairs” were made but -no spark!

I also went over the No Gas Problem before determining it was a No Spark Problem; Schrader valve, fuel pump relay , etc Fuel is fine

From the A6 receptacle on the OBD I’m reading two fault codes: 314 and 214. The 314 is “314 “Camshaft Position sensor (CMP) signal missing or faulty” and
the 214 is “214 Engine speed (RPM) sensor signal missing sporadically“ I now also get a 121; “121 MAF sensor signal” from A2 but when I first started this 121 fault was not indicated. Apparently I subsequently damaged the MAF while working on other problems. I have tested w/the MAF disconnected, and I have tested w/ the MAF connected but still no spark. I am under the belief that with the MAF disconnected I can still start the engine. At least get a spark. Pls advise if true or not.

So NO Spark, CPS fault and after reading this blog I also assumed the 214 was related to the crank sensor. So I replaced both the CPS and crank sensors and the primary coil in the non-starting 850 with the same parts from the starting 850. Still no spark. I cracked the Bakelite connector on the CPS while swapping so I went to the bone yard and got additional CPS, crank sensors and coils. Still no spark. I’ve swapped in two sets of CPS, crank sensor and coils one from a known working motor. BTW the parts from the boneyard were from a car w/ deployed airbags so I assume it was running up to point of collision

BTW: I’m jumping the battery from running car so the volts/amps are good. +13.5 at battery

W/ a VOM, w/ jumper cables & running car attached, I read:
Battery terminals: +13.57
at the CPS connector: +12.5V, +5V and 0V
I am dropping 1volt from battery to here but a) its more than the required 11.5 and b.)it’s probably due to line risistance
At the crank sensor connector: 0v, +1.67v
at the COIL: +12.5 at both “nuts” , connector: 0, 13.5, 00.15v (transient)
MAF (what the heck): 0,13.5, 0, 0

I am lost...
The battery volt/amps are good.
CPS, Crank sensor & coil have been swapped out. Voltages good
Schrador valve emits gas. fuel pump relay (103) has been swapped, I can hear the fuel pump when I turn key to position II. Fuses etc checked and good. Little stuff done
And yes the IAC humms, buzzess quite happily when key in second position. swapped out primary coil wire (twice)

Yet still no spark!!!!!!

ECU bad??? I hesitate to think this as it is a difficult TS w/o risking my spare car. What’s the deal w/ the ECU’s? Are they interchangable between a 93 850na manual trans and a 94 850na manual trans. The “numbers” are different on the labels between my two 850’s.
ECU numbers (standing in front facing engine)
Non-starter:
Right ECU (nearest to engine in BIG #’s) 4.1;
also on label: PO9146296; CP01, 1T2250685; T94050203
Left ECU: 1.2
plus PO9146476; CP01; 1T2852395; T94020348
Can someone provide an explanantion of ECU’s and interchangeability. On my (previously) running 850 I have a
Previously good engine
rightmost ECU 3.1; P03517961; CP03; 1T2250646; T92462263
Left ECU 4.2; P03517962; CP03; 1T2852210; T92480274
Can these be swapped? If you’re not sure pls don’t guess I don’t have another

Anyhow I don’t know what to do next other than giving up and throwing in the towel. I have a signal tracer with which I can trace for continuity on the wire harnesses but I don’t have a complete wiring disgram that goes to the CPS, crank sensor, ECU pin-outs etc.

Can anyone point to link to ECU pinouts? I’d like to know if the CPS and crank sensors are connected to their respective ECU connections

I’d try swapping ECU’s but that can be an expensive rathole. And since I don’t know enough ECU’s are a potential landmine for me

It appears I may have been following the wrong supposed “problem” with my emphasis on CPS, crank sensor etc but I just don’t know what to do next. I may get a buddy to come by w/ a truck and drag the 850 trying to jumpstart it but wow for the first time in a long time I’m clueless.

so:
no spark, fuel ok, good battery source (cablejump), swapped out supposed “bad” parts; CPS, Crank sensor, Coil for known good, and coil wire - still no spark. HELP

Any suggestions from those on this forum will be appreciated and tried.

Paulfr

 

You can find the technical documentation in .pdf form here: Volvo 850 Maintenance And Service Documents

As I recall, as this is a dealer manual, when you get down to diagnosing the ECU pins, it references a "breakout box" and there is no diagram of the ECU pins as you see them.

Have you tried removing the ECU and re-seating it? Personally I would not hesitate to swap ECUs and see if it helps. I have three '96 ECUs, two of them are NA tunes and all of them have completely different numbers on them.

Just make sure you disconnect the battery and let it sit a good while before pulling an ECU.

 

have you checked for power at the coil? You have swapped all the trigger parts but the main source of spark is that 12v lead. Check the red wire for voltage.

 

Thanks for sticking w/ me on this problem.
Yes there is power to the coil +12
Yesterday, I worked on my "spare" Volvo and returned it to running condition. It needs a new wated pump so it's not road worthy but It'll start and run.i gonna work one part at a time to determine functionality.

I'm pretty certain I have an ECU malfunction. I'll be swapping the ignition ecu out for another however I think I'll get one from the boneyard rather than risking the I have that's known " good". If it doesn't " fix" the non- starting Volvo I'll swap it into the working Volvo to deyermine if it is functional.

Has anyone tried constucting a breakout box using the pin connector in the basee of the ECU case? The brewkout box seems to be a pon board w/ labels and nice cabling.

Anyhow....BTW the Volvo maintemanve zip has a good write up on the OBD I diagnostics. Seems there are two additional test modes for ignition diwgnostics. More thwn static error codes. It's in the TS w/ test codes section.

i'll keep you updated.

Paulfr

 

I don't know if anyone has constructed a homemade breakout box/adapter. If you can find a wiring diagram for the breakout box, I'd love to construct one. Like I said before, I've never found the reference between the ECU pins and the breakout box terminals listed anywhere. And I've never had any reason to go poking in there with a voltmeter and risk shorting something, trying to figure it out.

Maybe one of the companies that do custom Volvo tuning have that information?

 

My 94 850na won't start - no spark. I've been trying for a week now and I've run through everything I know.
THe only sensor I haven't tested and confirmed okay is the Throttle Position Sensor (TPS) up underneath the throttle body.

Can a bad TPS prevent the ignition from from firing??

I have no spark from the coil and have tested/replaced everything else except this TPS sensor. . I have a second 850 that starts. It's my test bed.
I don't wanna remove the TPS cuz it's a PITA to do. The boltheads are rusted. nasty

I assume that even w/ a bad signal from the throttle body the engine should start or at least kick over. Does anyone know 'fer sure'???

BTW: Confirmed No spark from primary wire. have replaced the coil, cam position sensor, engine speed sensor (VSS), coil wire, battery, ignition ECU, fuel relay & main relay (underneath radiator cowling), cleaned grounds & connectors, checked fuses.

Still no spark. Any suggestions?

I think it wants to but.....

paulfr

 

Hey Paul, please don't start a new thread each time you have a different slant on the same problem. When you do that, people that want to try to help may not know all the other things you have done to solve the initial issue.

So, keep all of your NO SPARK stuff together.

 

If you clear the OBD trouble codes, do they return when you try to start it? If the ECU is not getting a cam position sensor signal, it will not fire.

If you are still getting the codes, I would imagine that there is a connection somewhere (that all of those sensors have in common) that is loose or damaged.

I notice that you have mentioned the "ignition ECU". Is your car one of the models with two separate engine management ECU's?

 

ECU pinouts on pages 7, 8, and 9!

http://trionic.mobixs.eu/Motronic/M4...onic%204.3.pdf

 

Mr Sandwich...
Hey thanks v much for remembering me regarding the pin out for the ECU's. Since I have swapped out all the spark critical and fuel critical parts with replacements from a working engine with no change (still no spark) I'm moving on to tracing signal lines. I' encountered a few wire bundles that were opened and then retaped with electricians tape so I think this problem has occurred before Probably why I got the car cheap.

I'll update you on my progress. I have a few motorhead friends stopping by over this wkend. We're a dying breed.
Paulfr

 

ooooo that sucks. But at least it is fixable, even if it's annoying. Perhaps you could steal the engine harness off a junkyard car.

 

I had a similar problem. The cam and crank sensor in my car were producing good signals at the sensor, traced back to the ecu pins the signal was arriving, continuity between ecu and the coil (receiving the signal from the cam sensor) was fine, still the car wouldn't start. It turned out to be a weak starter motor. The cam sensor requires a fairly quick pass of the magnetic pickup to deliver a signal strong enough to travel to the ecu, be read by the computer, and allow for return to the coil. Very tough to diagnose since everything appears to be fully functional. Same problem could probably be seen with a battery in a weakened state. Can you compare your different Volvos and see if the starter motor in the trouble car seems slower?