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Do you even still need help. Sometimes customers seek help elsewhere or figure it out on their own before we get to each and everyone.
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An ignition coil can premature fail from grounded spark plug wires or from poor power or ground to the coil. The spark plugs would not be to blame unless the end is smashed or the porcelain is cracked, using up all the power the coil is making.
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Do you want to hold off till you get a new coil to try?
That is odd, that reading was backwards. My diagrams for the year model are not great but it makes me lean towards the ECU.
I think its best I let another try, I am just not as certain as I would like to be.
Hi there. Different expert here.
Do you still need help with this issue?
I'm pretty sure together we can diagnose this no-spark issue, but first, can you tell me what series Volvo are you working on (240, 740, 760, 780), engine type and size (4 or 6 cyl, turbo or not), auto or manual transmission?
Sorry for the delay.
The usual suspects for a no-spark condition on the 240s are the radio interference relay, the power stage, or the crank position sensor. Please give me a few minutes more to finish digging up my notes. I'll be back in a bit.
Sorry about that.
Let's start by doing the easiest check first, which is the 25A fuse located in its own holder about a foot behind the battery on the driver’s side inner fender, next to the coil. This fuse holder tends to corrode and cause all kinds of problems. Check it not only visually, but by ensuring current is flowing through it.
If the fuse is not the problem, then we need to check the power stage:
Please let me know what you find and we'll take it from there.
Here are the attachments.
Great. Looking forward to hearing from you.
Let's not get ahead of ourselves and do this in a systematic way.
Regarding the coil resistance tests resulting in 0.00 Ohms, try another ohmmeter. Primary winding resistance must be between 0.6 and 1.0 Ohms, if not the increased amperage will burn something (resistance is inversely proportional to amperage - sort of like a see-saw, if one goes down, the other one comes up).
The fact that the engine momentarily started leads me to believe there is a bad connection somewhere in the circuit.
On test 8, you say you're getting between 1 and 2 volts which is too low. It should fluctuate between 0-12 volts. By-pass the 25A fuse and holder temporarily while you test the circuit. If OK, check the wiring to the crank position sensor. If it looks dirty or frayed, replace the sensor.
Please let me know what you find.
The reason I said try another Ohmmeter is because if yours is not calibrated, it might not be able to read down to 0.6 Ohms or so. If I were you, and just to be sure, I would check the coil at the parts store with one of their Ohmmeters.
Also, and since it is the most common cause for this type of failure, don't forget to by-pass the 25A fuse holder.
The crank sensor is on the bellhousing, above the starter - it's not easy to replace. last time I did one of those, I had to do it by feel alone with a stubby 10mm wrench.
Actually, it's not uncommon for a whole batch to be defective from the factory - try using a reputable name brand such as Bosch.
Just in case, here is the crank sensor test:
Sorry for me being a "worry wart", but did you by-pass the 25A fuse and holder? As I said previously, this is the most common cause for those low voltage readings.
NO, you didn't screw up. As I've been trying to tell you, that fuse holder is the most common cause of the no-spark. Go to the parts store and get a replacement inline fuse holder (click here for example from Advance Auto)
That was just an example. Make sure to put in a 25A fuse. And please, no crimp-on/butt connectors. Make sure the new fuse holder is soldered in and protected from the elements with heat shrink tubing (also available at the parts store)
Great. I'll log back in tonight to check on you.
The complete circuit that includes the 25A fuse is attached.
As a preventative measure, you might also want to replace (or at least have spares on hand) the EFI/FP relay and the crank sensor.
What do you mean? Did you replace the 25A fuse and holder? Did the engine start afterwards?
Do you mean there is voltage from the battery to the 25A fuse, but there is no voltage past it? If so, either the fuse is blown or the connection is bad.
I always recommend this free basic Auto Electricity tutorial (click here). You might already know all the stuff in it, but I thought you might use it as a quick refresher.
Not to worry. Replace the crank sensor and let me know when the engine starts.
If you're getting only 168 Ohms resistance, then either the sensor is partially shorted internally or you have the Red/Yellow and Blue/Yellow wires shorting together. Since the test is done at the ECU connector with the ECU disconnected, I don't think it is the problem.
To further determine the ECU is not the culprit, let's pull the any codes that might be stored in the system:
ENTERING SELF-DIAGNOSTICS (IGNITION SYSTEM) CONTROL FUNCTIONS
The system monitors the operation of certain components by operating the item(s) in question. When the component or switch is operated according to a set procedure, the LED will display a 3-digit code. Failure to display a code indicates the control unit has failed to detect operation of the component/switch. In this case, the fault lies with the component/switch, connectors and/or wiring.
The functional check system can also test whether components/switches are correctly wired. As an example, it can be used to check whether the permanent/magnet generator (engine speed sensor) and wiring are intact if the engine fails to start.
CONTROL FUNCTION NO. 1 (ACCESSING CODES)
This function displays any codes stored in ignition system ECU memory during engine operation. The system can store 7 different ignition system faults.
I don't know about jumping pins on the ECU. See the attachment for a test to check the crank sensor lead. Let me know what you find.
All this time we've been chasing a no-spark condition, but do you know if the ECU is pulsing the injectors? If not, disconnect any one of the four injectors and plug in a Noid light (available at most auto parts stores) in its place. Noid light should flash upon cranking the engine. Please let me know what you find?
I don't think I'm communicating effectively with you - I thought I had given you specific instructions on using a Noid light to check for injector pulse, yet you're talking about a fuel test and valves moving.
Also, if you replaced the 25A fuse and its holder as I indicated, you wouldn't have to test the power from the fuse to the ECU - you would know if it was there or not.
At this point I feel I'm not the best person to guide you through the tests required to diagnose your Volvo's issue. I'll opt out and re-open the question to the field so other experts may have the opportunity to chime in. Please don't reply to this response or the site will revert the question back to me.