A few weeks ago I posted about my daughters 740 wagon not starting ... after trying and failing several times... three days later it started right up.

well a storm front rolled through today and the car failed to start stranding her near her workplace ... I had put what I thought was a faulty Radio Suppression Relay back in the vehicle after confirming a good one from the junkyard and I sent her along hoping that if it failed again she could just replace the potentially bad relay with the good one and it would start up again, therefore confirming that original relay was bad. Well no go... it still didn't start after we had replaced the relay. So both relays are probably good and the RSR can be eliminated in my opinion.

So I thought that maybe the plug wires were wet from the rain and replaced those ... still no start, then I took off the distributor cap to see if it was wet in there but it looked dry and clean (we had just replaced it when we smashed the other one while replacing the transmission).

In any case her car is still sitting there and I'm wondering whether to have it towed back to my house again.

Is there any other parts of the starting system that would be effected by wetness? The original time it failed was during a rain as well so it feels like water is the problem.

thanks in advance!

Jack

So you have spark and fuel and it still won't start....Is the camm shaft turning? Is the fuel pressure adequate?

Well I have to assume so since after I wrote my last submission on this the car started again and seemed to be running fine.

I restarted it several times successfully and started buttoning it all back up and was about to go in when I thought I would start it again to make sure and it didn't start - same symptoms cranking but no start.

I would have posted sooner but the timing belt broke on my personal daily driver so I was down two vehicles and I'm having a run of bad luck with my fleet!

I think I should start a new thread titled - when do I take it to a shop?

I can't get past the feeling that the rpm sensor is flaky and causing bad ignition timing

maybe I'll title the new thread "Can I have spark and fuel but bad ignition timing cause the spark to fail?"

Hello,


I’m glad you’ve narrowed it down even further! Sorry to hear about your broken timing belt though.

You might try groping the crankshaft sensor cable to see if it causes any change in symptoms. If it does, you can be sure that it is causing your trouble.


Goatman

sorry I have been super busy and so haven't been able to get back to your guys set of recommendations... This morning I took my daughter over to the car and we tried all of your suggestions. Here are the results:

I have checked for spark and there is what looks to be intermittent spark (tester hooked to plug wire and grounded on engine, crank 4-5 times then one spark).

I pulled a spark plug and the hook part of the plug is dry but the center tip (main body of plug) is wet after several cranks. So I am pretty sure it is getting fuel

but I also tested the voltage at the injector wire and it seems as if there is 8-10 Volts on BOTH connection points of the injector wire???? Seems odd.

one suggestion I've received is that the system supplying spark should be continuous therefore supplying a regular ongoing spark rather than an intermittent one.

another potential point of interest - whenever the cranking is stopped a puff of white smoke seems to come out of the throttle body??? Maybe there's something clogged up in there??? blocking air maybe??

thanks guys and sorry for my inability to stay with this over the past few days. I am hoping to figure it out today. Researching possibility of distributor cap, ignition module, or another sensor failing while I wait for anyone's input!

Jack

Paul,

Nothing definitive at this end, but I can at least address your observations as I interpret them.

"I have checked for spark and there is what looks to be intermittent spark (tester hooked to plug wire and grounded on engine, crank 4-5 times then one spark)."
• Sorry but I can't come up with a solid comment here, not knowing what kind of "tester" was used, for one thing. Was it a spare plug? Or the kind of tester with a variable gap? And if so, what was the gap set at? Was there a good, solid connection to a good ground?

"I pulled a spark plug and the hook part of the plug is dry but the center tip (main body of plug) is wet after several cranks. So I am pretty sure it is getting fuel"
• It may just be getting a sip of fuel from the pump "prime" cycle every time the key is turned to ON. However, if it's getting "normal" fuel pressure, then we can assume (yes, I know) that the Ignition system is basically working, because its timing pulses are allowing the FI system to run the pumps. Even so, there could be a problem with/at the ignition coil. It's held on to the heat sink with 2 torx head machine screws. Try cleaning it's contact posts and the mating spring terminals shown below.

"but I also tested the voltage at the injector wire and it seems as if there is 8-10 Volts on BOTH connection points of the injector wire???? Seems odd."
• Another tricky one here. Because except for the short time each injector is grounded, it will have 12v applied to its ground side from its parallel connection to the other 3 injectors and the solid 12V being applied to (and thru) them.

In other words, the common ground side of all 4 injectors is not a solid connection. It's controlled by the ECU 4 times per rev (once for each cylinder). What I don't know is the duration of those ECU ground pulses. Or how responsive your meter is. But my gut feel is that what you saw was normal. At least until Art rings in to explain it weller, as only he can;-)
[This would be a good time to have a 'noid light to test injector pulses.]
['noid is shortened from solenoid]


"one suggestion I've received is that the system supplying spark should be continuous therefore supplying a regular ongoing spark rather than an intermittent one."
• Just one spark "interval" per plug per revolution. Might seem continuous, if looking at the coil wire, depending on engine rpms.

REX Coil removed from Amplifier heatsink


REX Coil connections


--
Bruce Young, '93 940-NA (current), 240s (one V8), 140s, 122s, since '63.

I did end up shortening the gap in my variable gap spark tester and it shows regular periodic sparks now.

good call Bruce

so I have spark and fuel - I at least got that figured out!

I'll try the RPM Sensor test and go from there

thanks!

Hello,


Since the car is now getting regular spark, you need to check if the engine starts with propane or starting fluid.

I was first to reply Tuesday and asked you this question 2 minutes after you posted for help. Please honor my assistance and find if the engine will start with fluid or propane.


Goatman

I will do it Goatman, ...

I did try this the last time that no start took place - I think you were involved in that thread as well? So I didn't think fuel was the problem... assuming that this is the same problem as the last time it didn't start....

I tried starting one more time and it almost wanted to turn over... on second cranking it was again a no start... then I opened the throttle body intake hose to prep for when my starting fluid arrives with daughter... I opened the throttle plate and smoke poured out of the throttle body???

starting fluid is arriving soon.

Jack

Hello,


You may want to take this time to check the valve timing. Ajar the timing cover and match the marks to the valve cover and crankshaft pulley.


Goatman

With Starting fluid sprayed into the throttle body (throttle plate open) the car seems to try to start but won't fully turn over. A couple more spritzes of fluid then the same thing... tries to turn over... no start then just cranking

the tension on the timing belt is very loose on the side opposite the idler pulley... if that means anything

I've removed all bolts holding the upper timing belt cover

"and match the marks to the valve cover and crankshaft pulley."

should I make marks on the valve cover and crankshaft pulley? or are there marks already in place that I need to line up somehow with the crankshaft pulley?

Stracker,


Check this out:
http://www.threefattigers.com/Protocore/Volvo/TimingMarks.htm


If it as you say, the timing belt is loose, then you have a problem.


Goatman

ok - do I need to take off the lower timing cover to confirm that my timing is off OR are the main crank pulley's marks (cuts in the metal of the actual 3 pulleys of the main crank) supposed to line up with the mark on the top timing gear (cam gear right?)?

Stracker.


Lining those three marks up on the crank pulley with the cam would be a nice quick check. The harmonic balancer can slip though if worn and cause the three marks to be off.

You can also use a compression tester to verify that the valve timing is correct.


Goatman

ok - so to review

my Crank Position Sensor is not the problem because I have spark and fuel

I need to confirm my timing is off

If my timing is off I need to confirm the harmonic balancer is worn and replace it.

Hi!


I had written another message, but it was truncated.

The harmonic balancer can slip because the inner and outer parts are bound by a piece of rubber. When the rubber fails, it allows the outer piece to rotate in relation to the inner piece. When this occurs, the timing marks on the outer piece do not correlate to the actual timing. Since the timing cog is keyed to the crankshaft, and is also a separate piece, the failure of the harmonic balancer will not affect the valve timing.

I am very interested about your statement that the timing belt is very loose.


Goatman

Well it started again and I have to assume that the mechanical timing is fine if it runs well when started.

after several starts it failed to start again

so can I have spark and fuel but bad ignition timing cause the spark to fail?

btw I did tow it home before halloween and the harmonic balancer was replaced about a year ago after it failed and cut two belts off the accessory pulleys.

I think I'll start a new thread - this one is looking scary with 34 posts!

You can tighten up the belt by loosening the tensioner nut and then retightening it again. Rotate the crank until both #1 cylinder valves are closed and you can look into the #1 spark plug hole and see the piston is at the top of it's stroke. The mark on the camm pulley then should be very close. The camm pulley keys have been known to shear off allowing camm timing to slip.

"so I have spark and fuel...I'll try the RPM Sensor test and go from there"

No point in testing the CPS Jack, if you have spark. It's the CPS that get the Ignition going. See the sequence below.


Start-Run Sequence LH2.4 or REX

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 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 white case with the Fuel relay.

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.

Determining whether or not there is spark at the plugs (2a) — and whether or not the plugs are getting gas (3b) — makes a good no-start "starting" point.

For example, if 2a fails due to a bad Power Stage/Amplifier, there will be a no-start with gas-wet plugs. If 2b fails (practically never) symptoms will be Fuel-related: a no-start with spark at the plugs, but plugs remain dry.


--
Bruce Young, '93 940-NA (current), 240s (one V8), 140s, 122s, since '63.

Thanks Bruce - very helpful!

yes I meant 1 spark per crank... and I do have a variable gap spark tester and I would say it's about 1/4" gap - that could be too big?

I'll try to shorten it and see if I get more sparks (at least one per revolution.

I'll also remove the coil and the ground connections and clean them all up to see if that helps before jaunting through the junk yard.

the picks are extremely helpful - thanks

Jack

Hello,


The clue here is the smoke coming from the intake, inidicating that there was either partial charge ignition during an intake cycle or the compression vented through an intake valve. This could mean either the valve timing is incorrect, the intake valve/train is damaged, or the spark occurred out of time. Since the ignition is computer controlled via a crankshaft position sensor, you should check that assembly for damage or defect.

Yes, potential is normal at both leads of the injector until grounded by the control unit.


Goatman

I checked the resistance across the pins going to the CPS and there is 140 Ohms across the middle pin to one side pin and an open circuit across the middle pin to the other side pin.

the test in the FAQ indicated the failed sensor had no resistance in between the middle pin and either side pin...

so it may be a flaky Crank Position Sensor?

Jack

Sorry Stracker,


I don’t have wiring diagrams for that model, and so cannot answer your question.


Goatman

I was wondering about the Crank Position Sensor...

I'll next do the test that is in the FAQ's for the RPM Sensor and see if that nets any results.

thanks Goatman!

ajck

Spark plug wet with gas and weak/intermitent spark equals ignition problem IMHO...If plugs wires cap n rotor are good I would get a JY coil and swap it after cleaning the internal contacts AND the external coil to chassis conections. I paid 40$ for mine. I dont recall from your previous posts, have you cleaned the main ground connections to chassis(on passenger frame rail and below power steering pump)?

I have not yet cleaned any connectors although I looked at the ground connectors by the front passenger side parking lights... they looked ok but could probably still use a good shining up.

I looked for a junkyard coil but none available in the one yard I searched

I'll look over all the internal connections and see what happens after they are cleaned up

The relay plug connections can sometimes shift and not make contact. To check the relay operation disconnect the injector plugs and turn on the ignition. You should have 12 volts to ground on one injector plug contact and zero on the other. No voltage means the relay is not doing the job for whatever reason. Clean all the ground connections on the inside of BOTH front fenders. I believe your car has a flywheel sensor and that may also be the culprit.

"So both relays are probably good and the RSR can be eliminated in my opinion."

I'm beginning to think the RSR can be eliminated. Period.
The 200 series has the same engine and FI, but doesn't have an RSR nor any radio noise problems that I know of.

Your RSR may be perfect, but will not work properly if the coil doesn't have a good ground. Mine failed intermittently, and weather may have played a part.

See THIS POST more on this with pictures of the RSR ground terminal.

--
Bruce Young, '93 940-NA (current), 240s (one V8), 140s, 122s, since '63.

Bruce,

Was the corrosion just in the area where the wires connect or was the bolt connection corroded as well. I sprayed some deoxit on mine and used oxgard on it. I don't think I made good contact with a small brush to physically clean it.

It did not occur to remove the whole bolt. That would be the best way to get and and make sure everything gets cleaned. On mine it is akward to get at it to clean.
--
Paul NW Indiana '89 744 Turbo 145K/ '90 745 turbo 127K

Paul,
I didn't try to isolate the exact failure point, just took it off and cleaned everything. If the relay itself ever goes bad I'll just bypass it, since the 240's run fine without it.


--
Bruce Young, '93 940-NA (current), 240s (one V8), 140s, 122s, since '63.

One simple test will tell you much, after an extended crank and no start session, pull a spark plug and see if it is wet with gas. Report back.

RSR is an electrical thing that affects fuel delivery,
Plug wires are an electrical thing that affects spark
Maybe it is an electrical thing and maybe it is related to the weather, but it has to be determined which system is being affected. Throwing parts at it may get a lucky hit, or a random one that doesn't really reveal the cause, apparently like what already happened when after 3 days it started, but the cause of issue is unknown.

It has to be determined if it's spark or fuel. Check those, but if there's spark then make sure the RSR was actually changed. I recall someone had no luck with that, til they realized they were changing the wrong relay.
I'd go to the fuel pump relay next.

Hello,


Does it have spark? Does the engine start with starting fluid?


Goatman