87 740 Turbo wagon, WEAK yellow spark.. at wits end..
 

Hi, I've posted before here about the 87 740 turbo wagon I have, that one day banged out the exhaust and never ran since.. this was last spring... So we pulled it out of the barn to try to get it running again. Many things were done initially in an attempt to get it going.. A real big issue was the disintegrated wiring harness. Replaced the first session were; The hall pickup, Cap, rotor, wires... tried several power stages from know working cars... swapped around coils... replaced fuel pumps, filters...timing belt is fine..still no dice.. gave up and parked it in the barn and closed to doors...

Fast forward over a year...

So after lots of BS, I've managed to get a harness from a 760 turbo, [with the help of Dave Barton.. kudos!] to work with some mods.. I even bought another ECU, figuring the toasted harness must have fried the ECU. So today I got the new modified harness in place and tried it...

Same old weak yellow spark...

I've researched this term "Volvo 740 weak yellow spark" [and various versions of this term for A VERY LONG TIME now.. [since the first round , a year ago..] with no real definitive answers... I'm at the end of my rope on this one.. I'll be damned if I scrap the car for something stupid, as I'm sure it is...

Today my son and I , [Brickerz, the same guy having the big 242 k-jet to LH 2.4 issues.. BTW, you guys are really a big help there.. much appreciated!] started probing the power stage plug.. 12v on pin 1 and 5, should be on pin 4... and nothing on pin 4... we cut and spliced wires to pins 4 and 5... so 1 and 4 have 12 volts.. still weak yellow spark... Something is messed up majorly here and this has to be a big part of the problem... the ground is good.. [with key on, btw..]. What gives?

I'm INCHES away from simply trashing the entire factory system and going with Mega Squirt 2.....

Any ideas? I'll even sweeten the pot with 50 bucks to the first person to help me get it going again...

Cheers,
Mike

you have an lh 2.2 system, while that kjet->lh conversion is lh2.4, I'm not sure the ignition systems are wired the same and/or use the same power module. the LH2.2 240's didn't use EZK ignition, our 1987 has Chrysler sparks, which is totally different (uses a bosch distributor, but has no power module)

sadly, I've got no greenbooks covering any of the 700 series lh2.2 cars.

lets start at the top. you do have +12V on coil pin 15 when the ignition is on? if you disconnect coil pin 1, and instead use a jumper wire and touch it to ground momentarily, do you get a fat spark when you 'untouch' it to ground? if not, then your coil is suspect.

now, power the coil AND the power module, and touch the power module's input wire to ground. same thing, when you release that, it should go ka-ZAP!

Hi pierce, at the car now.. Key on, using a jumper wire on clip to touch to ground.. No spark and jumper wire does the old arc welder spark when you brush over the bolt head I'm using for a ground.. Coil must be baked? I guess you're talking about the power stage? Unhook and jump which pin to ground? Remember I got the flaky wiring going on there.. Thanks, so at least I'm looking at a new coil?
Cheers, mike

Just ordered a new coil.. 67 bucks for that sucker... Picking it up tomorrow morning. Ill post the results. Perhaps this car has a collection of issues...lol

Interesting note... The known working coil on my 940 does the same thing with the test.. No spark at coil and touching wire to ground makes sparks. So maybe the coil is good. The nine starts right up... Hmmm

well, I don't have the pinout of the EZK that a LH2.2 740T/760T probably uses, so I really can't assuredly give you any pinouts.

the parts catalog says the power module is a 3501921 and the ICU (ignition control unit), mounted on the driver side of the dashboard, is a 1346469.

ok, heh, that PM cross references to 940 turbos, which are LH2.4, so I guess its the same PM as the later cars, so ok, my PM pinouts may be correct.

as far as the coil goes, any 12V bosch coil of the same size should be just about fine.


hahahah, the Bosch PM thats equivalent is used on tons of cars, even some Fiats (Fix It Again, Tony!)...

https://images.gasgoo.com/MiMgIzQzNz...vo-3501921.jpg
chinese clone of Bosch 0227100145 power module

ugh, that labeling is confusing. so again.

pins...

1. red-white wire to coil pin 1 (output of PM)
2. black wire from ground
3. grey shield around pin 5 wire
4. blue wire from ignition switched power
5. grey wire from ICU pin 16 (input to PM)

oh, this test, brushing coil pin 1 against a ground while coil pin 15 is powered.... you probably need to plug a spark plug wire into the COIL output and put a plug on the other end of it to get a spark, as your distributor isn't turning, and likely won't be pointing at any particular sparkplug when you do this test.

Yes, I left the coil wire in the coil tower, and propped the end of the coil wire about a quarter inch from a ground, brushed the jumper to ground and looked for the spark to jump.. nothing out of the high tension coil wire and only blue "welding" sparks at the end of the jumper.. just like a dead short. However, my nine has a known good coil and the same test produced the same results.. In disbelief, I couldn't imagine that coil being bad.. so I started the car.. fired right up.

Are these newer car coils wired or wound different internally, as this test would work in grandpas old ford truck, but maybe not with these new solid state ignition system coils? Perhaps theres something else in these new coils that make this test invalid..?

Power stage has 12 volts on pins 1 and 4, and 2 volts on 5 - cranking- , with the coil wires unhooked, as mentioned on the Volvo No-Start .PDF I've downloaded... Again, what would cause such a weak spark.. there is 12 volts to the coil.. I'm beginning to wonder if the 242 and the 740 now have a very similar problem...

Ideas?

Cheers,
Mike

ah, these are simple coils. the solid state part is the ignition module and ICU computer that manages it.

Update, Went this morning and picked up the coil. Came home and bench tested the original coil, the new coil and even pulled the coil from the 940 as well. All 3 has identical results.. i even used a solid piece of wire and stuck it down in the coil tower and bent it over in an arc, to within a quarter inch or so of the bench vice. Power in the + side with a battery charger, and touching the - clip momentarily to ground did nothing but a FAINT barely visible spark on ALL 3 coils... [70 bucks down the tubes..] So, the new coil went on the nine, the nine coil went on the 740 and the remaining coil was marked with a ? and tossed in the "spares" box..I have to wait for help to crank over the car and watch the coil wire to ground and see if there's any improvement in the spark.. but I really doubt there will be any change. Next up is to hot wire 12 volts direct to + from the batt and crank again I guess...

Mega Squirt keeps looking better all the time..

Ideas?

Thanks,
Mike

Another update..

I read thru more of this document;

http://www.stepbystepvolvo.com/Resou...20No-Start.pdf

and performed the relay check.. This involves peeling the cover off the fuel pump relay and watching the relays as you turn the key to start.. the second stage of the relay has not clicked, indicating coil or hall sensor... my moneys on the hall sensor, as the whole coil thing has been covered.

Any thoughts on this?
Cheers,
Mike

Hall sensor ordered.. Rock Auto is 20 bucks cheaper than the local parts house... So maybe thursday I'll know something else.

M.

Installed brand new Hall sensor..... Guess what? ... NO START... SAME WEAK YELLOW SPARK...

However, the second stage relay does no click when in the start position, as mentioned in the Volvo PDF I posted earlier. No second stage relay click is supposed to be either faulty Hall or bad coil... both of which are either brand new or absolutely know good. No the issue must be in the wiring somewhere.. the rotted engine harness was completely replaced...

I guess I got to somehow trace the power flow backwards thru the harness/stage of events, and see where the interruption is... [all the while saving for mega squirt..... ]

What a great start to the weekend...


BTW... this engine will not even fire with a big blast of starting fluid... nice, eh?

if by 'second stage relay', you mean the fuel pump half of the double fuel injection/fuel pump relay, if thats not clicking, its either a bad relay, or the ECU is never seeing timing pulses from the ICU.

if it won't start with starter fluid, then there's no spark. OR the timing belt is broken or way off timing.

Update for today, spent most of the day screwing arou d with the 740 trying to no avail to get it go run. So... I zapped the battery to full charge to ensure full power for spark. We checked and rechecked and argued over the timing belt and the alignment marks. My weak eyesight made things worse. So we aligned the lower gear with the notched washer do dad to the mark on the casting. The piston is at the top of travel. The side gear idler I guess had its mark the 3 o'clock viewed from the front. The top gear has the dot aligning with the mark in the rear of the plastic cover. So we go to start it.. Plenty of cranking speed.. Batt good.. Now it backfires very loud out the tailpipe. Then we recheck and fool with it, thinking maybe off a tooth.. Same deal.. BANG!! But I noticed it wants to backfire as soon as I turn the key to the on position without ever engaging the starter.. So what gives now? It's sparking and there's gotta be gas to make the bang.. This acts just like my old Chevy when it's 180 out of time... Bangs out the back.. How can this be when the marks are correct? Advice? My son says to junk it at this point.. I think it's gotta be something really dumb... Ideas?
Thanks, m.

spark plug wires in the wrong order?

http://0.tqn.com/d/autorepair/1/0/S/g/00000069.gif

The firing order is correct and matches that picture.

-Mitch