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Odd occasional hesitation under acceleration/boost

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Old Jan 15th, 2020, 19:43   #21
AllHailKingVolvo
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Well, new leads didn't make any difference at all! Not a jot. Will get my multimeter on the coil tomorrow to see if that is within range. It's the OEM Bosch unit so should still be on good shape after just 75k but who knows!

I have new gearbox oil due tomorrow too, I read recently that a guy with a B200FT in a 940 cured his hesitation issues with fresh gearbox oil, a long shot but something that needs doing anyway, so we will see. New fuel filter and a bottle of Forte will be going in too. Beyond that I'm somewhat stumped!

One thought is that I need to make sure the vac pipe is on the EZK and in good order. I should check ECU and EZK for electrical integrity too and reflow any dry joints. Not altogether sure where to find the boards but will hunt them out!
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Old Jan 15th, 2020, 22:36   #22
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Quote:
Originally Posted by AllHailKingVolvo View Post
Well, new leads didn't make any difference at all! Not a jot. Will get my multimeter on the coil tomorrow to see if that is within range. It's the OEM Bosch unit so should still be on good shape after just 75k but who knows!

I have new gearbox oil due tomorrow too, I read recently that a guy with a B200FT in a 940 cured his hesitation issues with fresh gearbox oil, a long shot but something that needs doing anyway, so we will see. New fuel filter and a bottle of Forte will be going in too. Beyond that I'm somewhat stumped!

One thought is that I need to make sure the vac pipe is on the EZK and in good order. I should check ECU and EZK for electrical integrity too and reflow any dry joints. Not altogether sure where to find the boards but will hunt them out!
I think it would be better to check the coil earth Phil - it earths through the bracket so clean the coil body and the inside of the bracket where the two meet with a rotary wire brush or emery cloth, also the mounting tabs and the inner wing (sorry, bulkhead on the red-blocks) where the coil mounts and the mounting bolts too. Also clean the top of the coil with brake cleaner or similar to ensure it's clean and check the +ve feed goes to the +ve terminal on the LT side of the coil, cleaning and if necessary tightening the LT terminals as you go..

The EZK unit is usually mounted just above the brake pedal, the engine ECU is behind the drivers kick panel.

On the upside of not getting an improvement with the new HT leads, you now have a good spare set for emergency use!
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Old Jan 15th, 2020, 22:38   #23
mocambique-amazone
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There is no vacuum pipe to the EZK if it's a LH2.4 system.

Good luck, Kay
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Old Jan 15th, 2020, 23:00   #24
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Check fuel pressure under load

NGK BPR7EY or Bosch WR5DC+

Highly recommend the Bosch

Distributor cap and rotor should be Bosch to
Leads Bourgicord

And check the O2 Sensor. They last maximum 80kmiles

This version runs a little bit lean because of pollution rules. Don't care about this.
Good luck, Kay
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Old Jan 16th, 2020, 08:56   #25
AllHailKingVolvo
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Thanks Dave and Kay, will check all the above today!
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Old Jan 16th, 2020, 13:04   #26
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So...the coil is the black Bosch type, and the outer can appears to be covered in a rubberised powdercoating. I've cleaned everything and the mount has a strong connection to earth, but I'm a bit foxed as to how it can earth itself through the powdercoating. Perhaps it's conductive, I'm not sure. It's all clean though, connections are definitely on the right terminals, the coil is original, I'm not sure how much these things degrade over time but it's not getting hot, arcing onto nearby components or doing anything else questionable.

I wonder whether fitting a higher powered coil would help? I'd imagine that the stock coils perhaps become a little "tired" over time and maybe a fresh high performance unit would help. I'm reluctant to keep firing the parts cannon at the car though as so far I've spent rather a lot on bits and the problem still remains.

Is the OBD socket in these cars useful in any way? I know it's an early version (sort of in between the flashing LED box in the older cars and the modern OBD II setup) but I'm wondering if it would be worth having any codes pulled from it to see if it gives anything away.
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Old Jan 16th, 2020, 14:36   #27
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Quote:
Originally Posted by AllHailKingVolvo View Post
So...the coil is the black Bosch type, and the outer can appears to be covered in a rubberised powdercoating. I've cleaned everything and the mount has a strong connection to earth, but I'm a bit foxed as to how it can earth itself through the powdercoating. Perhaps it's conductive, I'm not sure. It's all clean though, connections are definitely on the right terminals, the coil is original, I'm not sure how much these things degrade over time but it's not getting hot, arcing onto nearby components or doing anything else questionable.

I wonder whether fitting a higher powered coil would help? I'd imagine that the stock coils perhaps become a little "tired" over time and maybe a fresh high performance unit would help. I'm reluctant to keep firing the parts cannon at the car though as so far I've spent rather a lot on bits and the problem still remains.

Is the OBD socket in these cars useful in any way? I know it's an early version (sort of in between the flashing LED box in the older cars and the modern OBD II setup) but I'm wondering if it would be worth having any codes pulled from it to see if it gives anything away.
The original coating on the coil body was black paint, nothing more special than that. From your description, it sounds like someone has gone a bit mad with some Plasti-Dip :

https://plastidip.com/

What's meant to happen is the bracket cuts through the paint as it is tightened up to create the connection and earth that way.

Something else worth checking that i forgot to mention is the earth terminal for the ignition amp module. You know where the module is on the lefthand inner wing and there is a small bit of loom that plugs into it. From that loom is an earth terminal that goes to a screw not far away - check those connections are clean and good too.
While you're about it, it might pay to undo the two screws holding the module on, clean the old heatsink compound (the white goo that is no doubt rock hard after 25 ish years) off with a solvent (brake cleaner, IPA or similar from both mating surfaces, ensure both are bright and shiny (Don't use anything abrasive on them!) and smear some fresh heatsink compound on one of the surfaces. As you refit the module, give it a wiggle as it makes contact with the heatsink to spread the compound around evenly. This is unlikely to cure the fault, just good preventive maintenance but it might help a little.

Usually coils either work or they don't, if they are getting close to failing, you'll certainly know about it, it won't just be a flat-spot/hesitancy under load. With that in mind i wouldn't fire the parts-cannon in the direction of a new coil.
What i would do is check all the earth straps including the one from cylinder head to bulkhead are intact, clean and in good condition. Likewise the battery connections to body and also anywhere else.

The "not-quite-OBD-II" sockets in the centre cubby hole can be useful, there is a thread about a reader you can buy on here by Loki_the_GLT :

https://www.volvoforums.org.uk/showthread.php?t=285498

Something that keeps niggling in the back of my mind about this is the CTS - if it's the original it might be getting a bit tired or if it's had a replacement, was it the correct one?

0 280 130 032 is the Bosch number, seem to recall there's also one ending in 069 that's an equivalent. It might be the sensor is working fine and has just gone a bit out of tolerance, if it's running slightly lean under full load as a result that would cause the problem you're getting.
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Old Jan 16th, 2020, 15:04   #28
AllHailKingVolvo
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Excellent advice re the coil Dave, thankyou-I'll double check the earth straps on the head, block and ignition module too. Yes I think someone has had at the coil with some sort of plastic-y paint as you said!

I've ordered a new CTS (the Bosch unit as recommended, I remember putting a pattern one in my 744 and it going on the Fritz about a month later!) just to eliminate the possibility of it being a factor. I also have a new CPS on the way (should have arrived today, but the weather is horrendous so postie probably delayed) as the current one, whilst looking reasonable and devoid of any obvious sheathing damage etc, has really manky, green and discoloured connector blades. Not sure whether it effects anything, but it can't help and is surely indicative of the age of the sensor. I remember when the CPS went on my 240 and it became harder and harder to start, the new one really smoothed out the running of the engine... so that may help.
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Old Jan 16th, 2020, 19:18   #29
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So, fuel filter is changed (SO much easier on a 940 than a 740 due to it just being in line rather than on the pump cradle! Presumably the 940 has just the one fuel pump in the tank), which has improved throttle response and power, the old one was heavy and appeared to have something loose inside it, so was clearly past it.

Unfortunately, the miss under power remains, but there is also a bottle of Forte in the tank now which should clear any upstream detritus or sticky injectors. It's all very odd...the car has a ton of power now, I just wish it would deliver it more smoothly!
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Old Jan 16th, 2020, 20:52   #30
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Quote:
Originally Posted by AllHailKingVolvo View Post
So, fuel filter is changed (SO much easier on a 940 than a 740 due to it just being in line rather than on the pump cradle! Presumably the 940 has just the one fuel pump in the tank), which has improved throttle response and power, the old one was heavy and appeared to have something loose inside it, so was clearly past it.

Unfortunately, the miss under power remains, but there is also a bottle of Forte in the tank now which should clear any upstream detritus or sticky injectors. It's all very odd...the car has a ton of power now, I just wish it would deliver it more smoothly!
Yes, just one pimp in the tank Phil, no pre-pump/in-tank lift pump or whatever you care to call it. Changed in 1995 i believe to just the one pump.

If the new filter has improved throttle response and power that much, arguably once the injector cleaner has done its stuff, it should be ok but it's worrying that the fuel filter was as bad as you describe.

With that in mind, i'd suggest also checking the condition and tension of the timing belt. The fuel filter should be changed every 2 years/24k miles (although Volvo often seem to work on 10k/year mileage) so it should only have been 5k miles old if the current mileage is 77k. It seems as though it hasn't been done since 48k miles (if then!) from your description so implies other maintenance tasks have been skipped or not done properly.

My old 740GLE had allegedly had the head gasket done with a new timing belt under a year before i got it. I noticed every so often, particularly when it was working hard, the performance would drop off. Knowing everything was as it should be, the only thing i hadn't checked was the timing belt and when i did, it was flopping about like a loose twig on a tree. That prompted me to also check the tightness of the cylinder head bolts. Glad i did as none were done up properly, it's a wonder the thing ran at all!

Ordered a new timing belt and didn't use the car until it arrived and was fitted, sorting the head bolts in between whiles. Transformed the car, performance, economy and response much improved and no more flat spots/lack-lustre performance when it was working.
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