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Volvo S80 T6 1999 bad start, bad idle after overhaul

Help, Advice, Owners' Discussion and DIY Tutorials on the Volvo S80 model. Sometimes called an "executive car", the S80 was and continues to be Volvo's top-of-the-line passenger car.
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Volvo S80 T6 1999 bad start, bad idle after overhaul

Post by Joost » Thu Jul 16, 2020 2:36 pm

Hi guys,

I'm afraid I may have a puzzle for you yet... There are many factors involved, which complicates things. I will try to explain the situation. Please ask questions if you have any and make any suggestion that makes sense to you, please.

I’m having problems with my Volvo S80 T6 from 1999. I bought it about 6 months ago, soon the 4th gear dropped sadly… All other gears were still working and the engine was running fine.
I decided to overhaul the gearbox, because I wasn’t about to give up on the car yet. As I needed to drop the engine with the gearbox, I decided to do the engine while at it too.
Parts were hard to come by, especially in Covid time, so all in all, the car was sitting outside for 5 months. This week, I built everything back.

Parts changed in engine: piston rings, lifters, engine bearings, all seals and gaskets, turbo innerworks, all hoses, thermostat, waterpump, timing belt, etc. Head was taken off a donor car, as mine runs on LPG, and valves were wearing out. The donor head was resurfaced and pressure tested. I also changed out all the wiring harness insulation, as they become brittle in Volvo’s. The exhaust manifold was cracked (on donor also), which I had welded.

The gearbox has been overhauled, all seals, brass bearings, plates and frictions and actuators were replaced, along with the hub for 4th gear (actual problem in the first place) and the oil pump shaft. Some pistons were changed out for updated ones, as they come in a ‘problem solver’ kit.

When building everything back, I started the car (cranking to prime oil system first). The car ran started quickly after priming and running smoothly. After a while (engine hot), the idle was becoming rough and low (600 RPM), which even dimmed the lights. When switching the engine off, it was cranking fine, but starting very poorly if at all.

I read online about possible issues, and I had a feeling that it may have to do with the variable cam timing. Next day, I removed the belt again, aligned the cams (Exhaust cam with writing at the top half, intake cam writing on the lower half on the back of the cams.) I have the tool to lock the cams into place. I did, loosened the bolts at the front of the cams (3 small bolts per camgear as well as the hub for the exhaust cam. I marked the exhaust cam gear when the hub was rotated fully clockwise, put the belt on, crank still in place, locking tool for cams still in place, turning the hub fully clockwise when putting the belt on, with still slack in the 3 bolts, intake also with slack in bolts left. Put the tensioner back, checked crank timing again, still good. I turned the hub for the VVT fully clockwise (slack in the cam gear slots was enough) and tightened the 3 bolts. Tightened the 4 bolts for intake cam as well. Removed tool, turned engine by hand 2 revolutions, and all 3 marks were lining up again. So, I feel confident about the timing.

Built everything back, started the engine again, which started quickly and ran smoothly. However, when the engine was heating up, it began to run rough again, and again it wouldn't start anymore.

I have checked faultcodes, which are erratic. I mean; I have deleted intermittend fault codes, where no faults came back, but the at that same time, the engine was running very roughly at 500 RPM…

Fault that I have seen are the following:

3100 Impulse sensor, no signal
280A Upstream lambda sensor: invalid signal
902A Communication, throttle damper control unit
903C Electronic throttle control malfunction
928C communication fault
510F vehicle speed signal
912A Communication engine management unit

Some, all or none of these faults may be present when the engine is running roughly. Another thing I noticed, is that when cranking, I often see the RPM needle go to around 3000 instantly and very shortly. To me, this may indicate a bad RPM signal (engine speed sensor). When I waited for the car to cool down, it would start again, and running more smoothly, until it warmed up again.

What I have done so far:

- Tried another engine speed sensor (used, from donor car), which gave the same issues and no start either
- Put the engine speed sensor in aluminium foil to guard against flux from starter motor cable, putting the foil to ground too. I saw fewer RPM spikes after, but still saw some occasionally. No change in bad start
- Checked fuel rail pressure, which was fine
- Generator voltage checked, which is fine when car is running fine (13.2 volts), low when engine is running rough (11.8 – 12.4 volts)
- Checked all fuses in the motor compartment, all fine
- Removed the connector to the thermostat / sensor housing, to maybe have the computer bypass the engine temperature reading. It didn’t make any difference. The dash engine temp gauge is reading fine btw.
- Opening the ECM to check for corrosion and water ingress. It looked fine to the bare eye.
- Wiggling the cable looms, no change

There are 2 things that complicate the issue:

- The gearbox is not doing well yet. There are no fault codes, but the gearbox only goes forward, which includes Neutral and Reverse. Park works, but it’s hard to tell if the gearbox is still in gear then. If so, it puts a load on the engine, without it knowing it, I reasoned. The gearbox is definitely in park (can’t turn wheels, lever in park and display says P). I imagine that the ECM doesn’t know that the gearbox is still putting load on the engine if it is. However, I haven’t seen a difference in the gearbox, where the engine will sometimes run smoothly. I would think that if the load in on the engine, the idle would remain rough…
I also tried to bypass the issue, putting the lever in Neutral, while lifting the front wheels. This way, the wheels could spin freely, decreasing the load on the engine. There was no difference.
- The car runs on LPG as well as gasoline. I changed the O-rings on the LPG injectors too, but some wiring will go through the LPG computer and then to the ECM, because it needs to shut off the gasoline injectors, and fooling the ECM that all is well. However, I do assume that I will read fault codes when the LPG computer is the culprit, which I sometimes do, sometimes don’t.

I once came across a Mercedes once that would die when the engine got hot. It turned out to be a couple of capacitors that would heat up and give out. I am not familiar with Volvo’s doing that, but The problem seems to be very present when hot and I get fault codes which seem a little erratic (sometimes this, sometimes that, sometimes none when engine is almost dying…) Also, I’ve seen the code 3100 (Impulse sensor, no signal) active with the engine running poorly, but running. I am not sure if this engine running can run on cam sensor only, but many engines die when the speed sensor signal is lost… On the other hand, The car was starting, idling and running fine when I parked it 5 months ago and there were no obvious signs of weather related issues in the ECM.

Anyway, I am grateful with all the help I can get to solve this puzzle! Input on the gearbox would be nice too, but I am talking about the supplier of the parts too, as he is willing to think about it too. I don’t feel like giving up on the old gal just yet…
I have to work on the car beside my day job, but I'm willing to test stuff. Also, I can make pictures if it helps. Thanks!

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Re: Volvo S80 T6 1999 bad start, bad idle after overhaul

Post by bronco » Thu Jul 16, 2020 6:20 pm

I hate to say it but maybe you did too many things at once?

Maybe pinch the wiring harness inside the trans?

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Re: Volvo S80 T6 1999 bad start, bad idle after overhaul

Post by Joost » Thu Jul 16, 2020 8:19 pm

Hi Bronco,

Thanks for your reply. I do that sometimes.. I'm not sure how reliable the fault codes of the ECM are, but the ECU for the trans had no fault codes, so I wonder if that would help. Could you elaborate please?

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Re: Volvo S80 T6 1999 bad start, bad idle after overhaul

Post by Joost » Thu Jul 16, 2020 8:34 pm

Could someone maybe provide a pinout of the ECM please? I have an oscilloscope, so I could check if the signal from the engine speed sensor comes through, as well as the throttle body position sensor. Maybe some already brittle wires gave out when moving the cable loom during removal/install.

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Re: Volvo S80 T6 1999 bad start, bad idle after overhaul

Post by bronco » Fri Jul 17, 2020 12:16 pm

Joost wrote:
Thu Jul 16, 2020 8:19 pm
Hi Bronco,

Thanks for your reply. I do that sometimes.. I'm not sure how reliable the fault codes of the ECM are, but the ECU for the trans had no fault codes, so I wonder if that would help. Could you elaborate please?
Just thinking , the range selector switch is inside the trans , as is the speed sensor . I remember thinking when i did the tranny in the 2002 the wiring harness could have been pinched or otherwise damaged while i was fighting to get the side cover off . If you did the trans in the car you might have gotten unlucky in that way. Also it is possible to install the gear switch wrong , like off a tooth kind of, do the backup lights work in reverse and the engine start in neutral ?

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Re: Volvo S80 T6 1999 bad start, bad idle after overhaul

Post by Joost » Fri Jul 17, 2020 3:56 pm

Thanks for thinking along! I had the gearbox dismounted completely and hung in an engine stand, so I think nothing was pinched or anything. Also, when I move the shift lever, the display indicates the right gear, it's just that the gearbox want to go forward always, so also in N and R and I believe in P too, but is then locked, so can't be sure..

bronco
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Re: Volvo S80 T6 1999 bad start, bad idle after overhaul

Post by bronco » Fri Jul 17, 2020 7:35 pm

:( Well you have to pull the tranny again I think , that sounds like some sort of valvebody issue fluid being misdirected .

all gears except D-3 and D-4 have the input clutch applied , even neutral . reverse is the only gear that applies the reverse band it sounds like the reverse band is not holding. The input sprag is holding in reverse but without the reverse band applied you may be in some weird version of Drive-1 without the forward or low band , that might go for neutral also ?

warped or crossleaking valve body ?


There is probably a test port on the trans somewhere you can put a pressure gauge and get a reading in different gears and compare to a chart somewhere

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Re: Volvo S80 T6 1999 bad start, bad idle after overhaul

Post by Joost » Sat Jul 18, 2020 3:54 am

Screenshot 2020-07-17 at 08.39.09 (1).png
3 versions of valve links, 2 with IMS, one with clip, one with spring
I may have gotten along with the gearbox. I may have installed a wrong combination of manual valve link. There are 2 versions of valve links for these transmissions with Internal Mode Switch (IMS). One has a retainer clip, one has a retainer spring. I thought they would be the same, but I was told they are not. So, I will have to change that out first and see what happens. It does look like I have to pull trans/engine again... 🥺 I will upload a photo with the valve links. The IMS helps determine ignition timing, among other things. Although the IMS is installed correctly (display shows the gear I set the gear lever to), the oil pressure still puts load on, so maybe it's still having an influence on the engine. However, I had lifted the front wheel so they could spin freely, reducing the engine load, which made no difference.

bronco
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Re: Volvo S80 T6 1999 bad start, bad idle after overhaul

Post by bronco » Sat Jul 18, 2020 9:34 am

Valve 2 and 3 are the same as far as directing fluid but the retention method is different , so maybe your switch would indicate the gear your shifter cable has selected but the valve body is doing something different

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Re: Volvo S80 T6 1999 bad start, bad idle after overhaul

Post by bronco » Sat Jul 18, 2020 9:40 am

bronco wrote:
Sat Jul 18, 2020 9:34 am
Valve 2 and 3 are the same as far as directing fluid but the retention method is different , so maybe your switch would indicate the gear your shifter cable has selected but the valve body is doing something different

To clarify I mean even if the manual valve is not attached to the cable the electric switch will still indicate the cable moving the detents for each gear are there as long as that spring roller is bolted onto the valve body , the manual valve in the valve body could be free floating

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