Dear readers,
Hope you all are doing great. My family 1995 Volvo 940, non-turbo, Bosch system randomly does not start. I leave it alone for 20 minutes and try again, and it starts fine. The car has the following new components.
1- New Bosch ignition module
2- New in-tank Bosch fuel pump
3- New Bosch distributor cap, and rotor
4- New Crankshaft Position Sensor
5- New Bosch plugs
6- New fuel pump relay
7- The coil and plugs produce good sparks.
The car has its own mind, at times starts fine, and randomly does not fire up. This is quite baffling. I am not sure what else to look for anymore. I would appreciate your thoughts and any suggestions you may have.

Best,
Habib

I don't see any reference to grounds. Check the two grounds on the top of the intake manifold and the big blue wire from the back of the alternator.
--
89 240 wagon, 94 940, 300K, 94 940, 141K

Dear Joe,

I very much appreciate you taking time to respond to my post. I am not sure of your reasoning to focus on the grounds. Unless I am missing something. The car never had any issue with grounding. It is a mystery that when the car is parked inside the garage, it starts quite well with no hesitation. When it is parked outside, randomly fails to start? Today I replaced the Crankshaft Position Sensor by installing a Bougicord P/N 271949 in case. We are going to park it inside and outside and see what happens.

Best Habib

I just felt it worth the thirty seconds to check. I hope to hear the conclusion to this puzzle
--
89 240 wagon, 94 940, 300K, 94 940, 141K

Hello everyone,

This post is to provide an update concerning the subject car and let you all know that for the past couple of days, I have parked the car inside the garage, the car starts and the engine fires up without any hesitation. The car’s behavior has been quite peculiar. However, I think if I can find it, there is an electronic component on the car which indicates “do not leave me outside” that I will replace. I must express my sincere thanks to all of you for taking time to respond to my post. You all have a great day.

Sincerely,
Habib

Dear Habib,

Hope you're well and stay so! If parking "indoors" is curative, that suggests the intermittency is due to: (a) temperature and/or (b) humidity.

The crank (RPM) sensor is humidity-sensitive. A crack in the outer insulation sheath can disrupt the signal. As others have noted, the your new RPM sensor may be defective.

When the RPM sensor's signal is lost: the engine will crank but get no fuel because without the RPM sensor signal, the engine control module (ECM) does not let power go to the fuel pump. This is a safety feature. If a collision smashes the engine compartment and the engine stops turning, the (ECM) turns-off the fuel pump: no fuel can spray where there may already be a fire..

When you get the Bougicord RPM sensor, park the car outside, and see if that makes a difference.

Note that a layer of corrosion on an electrical connector - that disrupts a circuit - need be only a couple of molecules thick and so invisible to an unaided eye. To remove such corrosion, use an aerosol corrosion-remover, e.g., Deoxit.

Hope this helps.

Yours faithfully,

Spook

Dear Mr. Simkin,

I cannot emphasize enough how appreciative I am for your time and graciousness in providing much useful and valuable tips and information. The new crank Bougicord sensor should arrive in the next three days. I will certainly keep you updated. Again, thank you very much for all your help.

Respectfully,
Habib

Hello everyone,

I would like to extend my sincere thanks to everyone for your time and input concerning the subject matter. I really appreciated it.
The car has become a peculiar issue. Yesterday, I tried to start the car at least 8 to 10 times without any ignition. At 7.0 pm in the evening, I tried one more time and the engine fired up without any hesitation, just like a brand-new car. The temperature was around 74 degrees throughout the day. It appears to be a component that is functioning intermittently. Without having access to a computerized diagnostic equipment, it is difficult to pinpoint the problem. Since the car is twenty-seven years old, I have ordered a Bosch ignition coil to be on the safe side. Wish all a safe and happy Holiday weekend.

Best,
Habib

Dear Habib,

Hope you're well and stay so. I suggested scrutiny of the ignition switch, because on a '94 940, I had extreme intermittency of air-conditioning. Sometimes it would work on first request. At other times it would suddenly start working, after a long delay. I had thought the problem was a failing relay, on the main control board, in the climate control unit.

The ignition switch failed: it would no longer turn smoothly. I replaced the switch. The air-conditioning began to work flawlessly. Although the key fit smoothly and snugly - as it should have - the problem was in the electrical unit, which is secured to the metal housing, by two flat-head, slotted screws.

How many miles on your car? After 27 years of service, the ignition switch does not owe you.

Enjoy the rest of the weekend!

Yours faithfully,

Spook

Hello Sir,

I very much appreciate your concern. Since I have installed a lower quality crank position sensor three months ago, I have placed an order for a crankshaft position sensor - bougicord P/N 271949. Despite measuring 0.9Ω on the primary, and 7.7kΩ on the secondary of teh coil, I have read some articles that the coil may still malfunction under the load. To be on the safe side, I also ordered a Bosch coil on Amazon.
The ignition switch is really tight and snug. However, I will follow your recommendation after I install the crank sensor and the new coil. But away, the engine fired up last night just with one start, and again it would not start this morning. Apparently, a component is functioning only intermediately. Ironically, my OBD coding reads 1-1-1. Again, thank you for your time!

Best,
Habib

When you checked for fault codes did you scan the system with the probe in both sockets 2 and 6?

Hello Chris,

Thank you for reaching out. I appreciate it. I scan the # 2 and # 6 more than twice, while the ignition switch was in second position. Each time the codes were 1-1-1. I must tell that she fired up this afternoon with no issue however, I am not so sure as to how she will behave tomorrow.

Thanks,
Habi

If you still have the old distributor rotor put that back in. I had a new distributor that came complete with cap and rotor. A.week later the rotor started failing . They have a 1k resistor resin into the top of the rotor. They can fail. Also make sure you distributor cap center carbon pin is in place. I've seen them drop out sometimes. Have you also checked you ignition amplifier for functioning. I carry several relays and spare parts with me in my old 745t.

Hello,

Thank you for your time and attention. I appreciate it. No, I did not keep the old rotor. I must remove the cap and check the rotor and everything else. I also will check the ignition amplifier. It is a bit strange that last night the engine fired up with only one start flawlessly, and this morning she wouldn’t start again. I think there must be an electrical component functioning intermittently off and on. Have a great day,

Thanks,
Habib

If it's the original ignition amplifier then the heat sinking paste has dried out. A good check is spraying the unit with keyboard cleaner which chills the electronic componant. Their heat sensitive and needs the heat sink paste so to transfer the heat to the metal plate it's mounted on. .

hi habib,

did you check for OBD codes?

bill

Hello Bill,

Yes, all am getting is 1-1-1.

I did order a crankshaft position sensor-bougicord 271949 and should receiving it within the next four days. The previous one I installed three month ago was not a quality part, just to make sure.

Thanks,
Habib

Dear Habib,

Try to get codes from your OBD box located in engine compartment near the strut tower driver's side.

Your symptoms looks like crank sensor intermittent failure. Thats why you don't get spark sometimes. When car's computer can't sense the engine turning no signal send to ignition module to activate ignition coil.

Yes I see that you have replaced the crank sensor but failure of new part still happens. What to do? Just get another one. Preferably Bougicord brand or Volvo original. Its price may have increased nowadays but thats something unavoidable. For mission critical item (thanks Spook!) its best to get any of these two.

Can't see why you're worried about the ignition coil. Is it because thats the item you haven't replaced? Bosch coils for 900 series is very robust that even some are being sold as used item still works well no problem. I have new Bosch coil with 10k ohms secondary winding (made in Brazil) and old used from eBay with 8.5k ohms secondary (made in Germany). Both works flawlessly.


Amarin

Dear Amarin, Greetings;

It is a pleasure to hear from you again. Thank you very much for your time and suggestions. I sure appreciate it. I must admit that the previous cranking sensor I installed was not a high-quality part. Considering your suggestion and other folks’ recommendation, I just placed an order for the Bougicord Crankshaft Position Sensor P/N 271949 through eEuroparts.com for $30. The sensor is being shipped from the State of Connecticut and should arrive at our home within the next four days. Again, thank you and have a great day!

Best,
Habib

Dear Habib,

Hope you're well and stay so. When the car does not start, do the instrument cluster warning lights come "on", when you turn the key to start? If these lights don't come on - and if the car is electrically "dead", i.e., no lights of any sort come "on" - that could mean a failed ignition switch.

Does the starter motor turn at all, i.e., does the starter turn the crankshaft, but does the engine not "fire-up"? Or, does the starter motor not make any noise at all.

Is your ignition key on a large. heavy key bunch? I ask, because over the years I've seen posts that suggest a weighty key bunch can cause an ignition switch to work erratically, and - ultimately - not at all.

Hope this helps.

Yours faithfully,

Spook

Dear Spook,

Thank you for taking time responding to my post, dated July 1, 22. In response to your questions, all the cluster lights come on when turning the starter key. The starter motor is strong and the engine crankshaft is turning when trying start. The key to the ignition is a single key.

Last night the engine fired up only with one start and this morning it would not start. I disconnected the Air Mass Meter cable, it did not start, and connected back with no start. Have great July 4th Holiday.

Thank you,
Habib

Check your fuel pump fuse for corrosion and melting. The new relays are poorly made
depending on brand. Does your local auto parts store loan tools. If so, ask.for the fuel injector "Noid" light that test if your injectors are getting power. I had to replace the "radio relay" for the injectors on my Volvo to get it running.

Hello Nahtanha,

Thank you for your time and attention. Please see my response to bill concerning the fuel relay/pump. Again, thank you.

Best,
Habib

Hello Nahtanha,

Thank you for your time and attention. Please see my response to bill concerning the fuel relay/pump. Again, thank you.

Best,
Habib

hello habib,

others have rightly suggested the rsr is the likely culprit.
and you say that you have a "new" main fuel relay...
is that "new" or possibly a different relay as a pull from a junkyard?
i've had brand new fuel relays fail quickly.

before throwing parts: when it quits,
you can confirm that these two critical fuel relays are working ok
by measuring for +12vdc at fuse 11 (main fuel pump fuse).
put your ground lead to the cigar lighter ground
put the positive lead to the top of the fuse 11 metal leg.

you will find the rsr in the far right engine bay between the battery and the
power steering reservoir, up high just under the main harness.
it unbolts with a torx t-25? and has the usual two latch harness connector.
use dielectric silicone on the pins when installing.

good luck, bill

Hello Bill,

Thank you very much for your time and attention. I ordered the new Bosch fuel relay and the Bosch fuel pump from Amazon. I discounted the main fuel line on top of the injectors rail and while placing the fuel line discharge port inside a jar, my wife did a few starts and there is a good pressured stream of gas pouring inside the jar. However, I unplugged the coil wire from the distribution, and held the end of 1/8" to the engine block with absolutely no spark. Did test on the Coil, and the coil is within the specification (0.9 Ω on the primary and 7.7 kΩ on the secondary). Despite this, I am befouled now as to why there is no spark from the coil. Hope you have a great day.

Best.
Habib

a single wire inside a bundle of broken wires can pass a continuity and a resistance test. won't pass enough voltage though.

turn key on, check for 12 volts with a meter on both spade terminals of the coil. has 12v on both? using a test light on coil terminal 1, red/white wire, have someone turn the key and try to start the car. the test light should pulse on/off. this is the signal for the coil to fire.

if you don't have 12v to the coil, then there's a break in the wiring or a dead ignition switch. if you do have 12v on the blue wire only, tap the starter and look at the red/white wire again. sometimes in mid cycle the coil won't show 12v on both. if you never see 12v on the red/white wire, then there's a break in the wiring in the coil---VERY unlikely.

if you have 12v at the coil and no trigger on the red/white wire, it's either the crank sensor on the flywheel or the ignition module on the fender. given it's seems to be temperature sensitive, my money is on the crank sensor. i see you replaced it but sometimes new means never ever worked. brand is important. volvo original or bougicord only. if you need an ignition module, bosch only, not huco or any other brand.

to test the crank sensor, you have to have an oscilloscope. they too will pass a resistance test and not work.

Dear Chuck,

Thank you very much for taking time to respond to my inquiry concerning 95 Volvo 940. Since some other folks made an emphasis concerning the Crank position Sensor, I placed an order for a bougicord sensor which I should receive within the next four to five days. Hopefully that will resolve the problem. Have a great Holiday weekend.

Best,
Habib

ok habib,

no spark- check that you get +12vdc to the blue coil wire with the key in run position ... maybe kaput ignition switch as spook suggested?

bill

Hello Bill,

The ignition switch is solid and good. No loose movement at all. The engine fired up last night just with one start and running very smoothly. This morning it wouldn’t start again. Since the car is 27 years old, I have a Bosch coil coming to me within the next couple of days. Am anxious to see! Have a great Holiday weekend.

Thanks,
Habib

Consider a failing injector relay, aka. radio supression relay, engine compartment, clipped on a rail, on your NA it should be up by the ABS unit (on turbo's by the power steering reservoir). Easiest way to diagnose this is by swapping with the identical fan control relay next to it to see if it now starts. As I recall the fan relay (grey, red, green and two black striped wires) is the forward one and the injector relay (pink, brown and two yellow striped wires) is the rear one. In a pinch you can drive a short distance without the fan as long as you watch the temp gauge carefully. There's also a bypass you can do there with a jumper wire. See this section in the 700/900 FAQ https://www.brickboard.com/FAQ/700-900/EngineFuelinjection.htm#Radio_Suppression_Relay

Another way to diagnose a failed relay is by cycling OBD Diagnostic Test Mode 3 (Injection System Component Activation) on port 2 of the diagnostic connector to hear/feel if the injectors are ticking and by feeling the relay. Note that sometimes this test will incorrectly pass if it gets a sticky relay temporarily working again, which is actually good to know. See this section in the FAQ https://www.brickboard.com/FAQ/700-900/EngineOBDCodes.htm#FuelInjectionandIgnitionDiagnosticCodesi

I'd normally suggest a failing ignition power stage relay as another possibilty for an intermitted stall or no start that might be temperature related, but you wouldn't have spark.
--
Dave -still with 940's, prev 740/240/140/120 You'd think I'd have learned by now

Dear Mr. Steven,

Thank you for your time in responding to my post,dated July 1, 22. The car has a brand-new radio suppression relay P/N 1323592. I pulled the ignition coil cable off the distributor and held it 1/8" close to the metal with absolutely no spark. I tested the coil using a multimeter and between the primary coil the reading is 0.9 Ω and the secondary 7.7 kΩ respectively. Any chance you could please help me understand that despite a coil within resistance specification range, what would be the reasons for not having spark at the coil? Thank you for your time.

Best,
Habib

Hello Habib,

Your original post said you had good spark.

With what you're saying now, I'd normally put the rpm crank position sensor at the top of your hit list, but you said you replaced it. If the ignition module can't see the engine turning over it will not provide spark. If you're at all in doubt about the new sensor, there is a test you can do at the OBD connector (DTM 2 on port 2) to help verify the rpm sensor during a no start period. Removing the ignition wire for this test is optional, it just keeps the engine from starting. If the engine does happen to start then of course you know you are not in a no start period and the rpm sensor is working at that particular moment.

That leaves the ignition switch, the power stage relay (ignition amplifier) and the coil itself on the top of your suspect list. Others are giving you guidance on some of the testing you can do.

For a worn igntion switch, have you had any cranking issues? -that's often the first sign of a worn switch. When the engine is running, does pulling it out a bit, lifting the key up/down, leaning left/right combined with turning it a hair cause the engine to hickup or die? When the engine won't start, do the backup lights still work? That will verify that power is getting to the coil on the blue wire (which comes straight from the ignition switch, unfused). When it does finally start, is it almost always after simply waiting a few hours for things to settle down or is it more the case that turning the key enough finally helps start it?

If it starts more often when the engine is cold overnight and misbehaves more when the engine is hot after a run then definitely suspect the power stage. In addition to an internal failure, the heat sink paste can dry out and cause temperature related problems there. For a failing power stage, as the problem advances the engine will normally start misbehaving during running causing it to die, but initially it may only be starting issues, typically when trying to restart right away after a good run. See the FAQ here https://www.brickboard.com/FAQ/700-900/ElectricalIgnition.htm#IgnitionAmplifer

There's lots more info in that FAQ ignition section on the type of problem you're having.
--
Dave -still with 940's, prev 740/240/140/120 You'd think I'd have learned by now

Hello Dave,

Sorry about the confusion. Yesterday when I had my wife to start the car, I was getting a weak spark from the coil by holding the end of the cable against the block. My confidence level concerning the spark was based on the ohm reading I extracted from the coil primary and secondary using a multimeter. I also read in some article that a coil might be faulty despite showing good ohm reading. Considering that and since the car is old, I ordered a Bosch coil today from Amazon. But this afternoon I went to the driveway and tried to start the engine. The first start she had a minor hiccup, but the second start the engine fired up and started running very smoothly. While the engine was running, I tried to move the key in the ignition around and did not notice any movement and the ignition was quite solid in place while the engine was running nicely. Again, thank you for your time and the link.

My very best,
Habib

It is rare for our Bosch coils to go bad and even rarer for them to fail intermittently such as to cause an intermittent no start. If you've got a decent meter and the coil resistance falls within spec (see the FAQ) and if the engine runs okay once started then that moves the coil way, way down on the suspect list. If the coil becomes weak you will likely notice increased performance issues and plugs fouling long before it causes a no start.

The spark often seems weak when testing the coil wire against the block unless you do it often enough to know what's normal. A better way is to pull a plug and witness the spark (easier to use a good spare plug). Also better to witness it in subdued or dark lighting. Spark often looks weak on a sunny day or under bright lighting, also if you've got a weak or failing battery.
--
Dave -still with 940's, prev 740/240/140/120 You'd think I'd have learned by now