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940 no spark, no clues

naterhater

Member
Joined
Jul 2, 2013
Location
Portland OR
My car ran, but something didn't seem right. It didn't idle well and the tach was doing strange things. After searching around here i suspected the crank position sensor was failing, so since its only $35 i replaced it. This didn't really change anything. The tach was still doing strange things, and the last time i drove it, it started running worse.

The next time I went to start it, the engine would turn but it wouldn't even try to run on its own. I determined that it is getting fuel but no spark. I started by checking the plugs, definitely not fouled. Then I checked the wires, they all had acceptable resistance. I checked the coil, the primary and secondary resistance are both within spec. The next logical thing to check was the power stage. I checked in the versions of the green book that are available online and could not find the troubleshooting info for EZK 116 so I looked in the other sections and found info for checking what seems to be the same power stage. I verified that the power stage is getting power, ground, and a signal from the ignition computer. Based on this I concluded that the power stage must be the culprit and replaced it with a brand new Bosch unit.

This has not fixed the problem and I am now at a loss. The engine is mechanically sound and it appears as though all of major components of the ignition system are functional. What could I possibly be missing??
 
its a 1993 940 Turbo, B230FT with LH2.4 and I believe it has EZK116. I never actually checked the crank position sensor. I read a post here that said, "its only $35 so if you suspect it then replace it" so I put a brand new OEM sensor in. It ran the same for a few weeks after putting in the new sensor. Is there a way to test it without an oscilloscope?
 
Just a guess, but check it for ac voltage in hz? Although I would be more focused on checking that circuit for an open or high resistance
 
No codes from either computer. But the "service" light was on

Which circuit should i check for AC voltage?

Also, all the fuses are good
 
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How did you check for spark? Have you physically checked for spark by holding a grounding a plug (connected to the wire) against the engine, and cranked? No spark? Unplug the coil plug from the distributor, and plug a spark plug into the end of that... (Coil-->Wire--->Plug). Crank again. Still no spark? That would at least verify it is further up the line.

If you check the wiring diagram, you should be able to trigger spark via the power stage. Perhaps just grounding... If that does work, then perhaps your ECU signal is not so good after all. EZK is fairly simple... Start testing up the stream, and see where it fails.
 
I put a timing light on the #1 plug wire and also tried it on the coil wire, it didn't blink in either place. Which wire would I ground to trigger the power stage?
 
I put a timing light on the #1 plug wire and also tried it on the coil wire, it didn't blink in either place. Which wire would I ground to trigger the power stage?

Timing light will certainly do the trick.

Somebody correct me if I'm wrong... (I'm not an LH2.4 expert...) but if the power stage fails, you WILL have fuel and tach working.. (tach will bump as you crank it...), just no spark...

Whereas crank sensor failure would present you with no tach during cranking, and still no spark...

If you just replaced the crank sensor, as well as the power stage.. then you may want to look at faulty wiring, or a possibly bad EZK box. (It does happen.)
 
I'd start by checking for power at the coil + terminal, if between that and a good ground point (not the "-" terminal; ignition switched on) you don't see battery voltage, I'd check the radio suppression relay, on the front of the left strut tower. Failure with that relay are so common, don't remember the wire colors to jumper, but you can (with some difficulty) pop the cover off and squeeze the relay closed, then try starting the car.
 
I had power at the coil+ but im not sure what the resistance is between the power stage and the coil. Next chance I have to work on it I'm going to check the wiring. As in, pull the connectors off the computer, power stage, coil, etc. and check them until i *hopefully* find something.
 
Stupid Volvo!!

Update:
I took my car to the only guy in town who is good at working on 20+ year old european cars. After all of his testing he has determined that the condition affecting my car is intermittent. Apparently yesterday after a while they unplugged the MAF and it fired right up, they plugged it back in and the car continued to start when they checked it over the course of the day. This morning they went to try it again and it wouldn't start. They determined that the signal coming from the crank position sensor will intermittently drop to zero but will be operating within the normal range when it is working. It has continued to start when they checked it all day today. They are keeping the car at the shop tonight to see if it acts up again tomorrow morning. I'm guessing I'm going to have to pick up this car tomorrow without knowing the root cause of the no start.

I had replaced the crank position sensor about a month ago and it ran fine for a few weeks before all this nonsense. This leads me to believe that the issue is one of three things; 1. The new crank sensor was defective right out of the box. or 2. My fuel or ignition computer is failing (fuel computer has TLAO chip, stock black ignition computer) or 3. The wiring is defective, as in a squirrel bite or corrosion. I dont have a known good computer to swap. But I do still have the old crank sensor that the engine ran with.

Which problem sounds most plausible? Whats the next step in diagnosing this?
 
its a 1993 940 Turbo, B230FT with LH2.4 and I believe it has EZK116. I never actually checked the crank position sensor. I read a post here that said, "its only $35 so if you suspect it then replace it" so I put a brand new OEM sensor in. It ran the same for a few weeks after putting in the new sensor. Is there a way to test it without an oscilloscope?

You sure it was a quality cps? OEM? I only go OE Volvo (from Tasca) on a cps. I think I paid more than 35 bucks for one.


intermittent issues sounds like a faulty cps.
 
I got the Bougicord cps from IPD, who knows if thats any good or not. Could the radio suppression relay possibly be the culprit? since the problem is so intermittent
 
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Maybe this will be helpful, it goes step by step.

Start-Run Sequence LH2.4 or REX-Regina

1) During starter cranking, the Crank Position Sensor sends timing pulses to Ignition Control Unit (ICU = EZK or REX)

2-a) The ICU uses these CPS pulses to trigger the Power Stage (aka Ignition Amplifier), which initiates spark from the coil.

2-b) At the same time, The ICU also propagates the pulses to the FI ECU, to allow (initiate) FI operation. No ICU pulses means no FI operation.

3-a) The Fuel Injection (System)* relay (previously energized at Key On) powers the AMM, IAC, ECU, Injectors, and Fuel (pump) relay coil + side.
* The System relay is in the rectangular white case with the Fuel relay.
* NOTE that on 700/900 cars with the square Hella pump relay, the RSRelay becomes the "System" relay as described above.

3-b) When ICU pulses are received by the FI ECU, it "energizes" the Fuel relay by grounding the relay coil (– side) to run the fuel pumps.

When all these things work, the engine runs until the Ignition is switched off, which in turn shuts down the FI system.
--
Bruce Young, '93 940-NA (current), 240s (one V8), 140s, 122s, since '63.
 
I got the Bougicord cps from IPD, who knows if thats any good or not. Could the radio suppression relay possibly be the culprit? since the problem is so intermittent

I would think the CPS from IPD (Bougicord) would be high quality but you never know?

My understanding is the suppression relay powers the injectors? Your OP said you had fuel and no spark? My internet guess would be CPS, Power stage, ECM, in that order.

If your getting fuel, and the fuel pressure is per spec. make sure you pull the fuse while cranking.
 
If the car is starting/running intermittently, then running poorly, you must have codes set in the LH2.4 system. Use the "black boxes" on the drivers side innerfender near the top of the strut.
These will capture the intermittent failures, or at least give you a short list of suspects.

Don't believe MAF causing a no start.....the proof is that your car will run with a dead MAF (when it's healthy and running, just disconnect the connector). It won't be happy, but will run in "limp mode".

For some excellent troubleshooting 411, use the Brickboard 7/9 Maint. Pages.....the best single collection of DIY troubleshooting for our cars that I've come across in 14 years of Swedish cars. These instructions will walk you thru how to access the stored fault data. It's actually one helluva system......

Oh yes, brand new parts die shortly after installation.....we call it "infant mortality". If it runs flawlessly for a week, it will likely run for years.
 
Problem solved. It ended up being the crank position sensor. I just had to put the old one back in, in the grocery store parking lot, to get it to start. All in all, a $35 dollar part i didnt really need in the first place ended up costing me around $350 in other parts and diagnostics.
 
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