1999 V70 XC Misfiring Problem

[DavidsVolvo]

I have a 1999 XC V70 with a light duty turbo. The car started misfiring a few days ago. The engine runs ruff at idle, has decreased gas mileage, less power and smells from the exhaust. I understand that this is probably resulting from misfiring for some reason.

I have an Autel code reader and it is telling me the following codes; (9160 Throttle unit internal fault and faulty signal; 3502 misfire, at least one cylinder; 3503 Misfire, at least one cylinder; 3523 Misfire three-way catalytic converter -faulty signal permanent fault; 3522 Misfire, emission faulty signal permanent fault).

I reset the codes and the only one that will not go away is the 9160 and the car is still misfiring. I replaced all the plugs and bought a new coil pack. I substituted each of the cylinders with the new coil pack (one at a time). There was no difference, the car still misfires the same way and the codes eventually come back.

What could it be? What else do I look at?

[precopster]

The failed throttle unit starves the engine of air so misfires result. Long term failure of a throttle unit can result in catalytic converter damage. If you've already swapped coil positions you have eliminated the coils as suspects. The 9160 code is indicating one of the potentiometer strips in the throttle has failed.

That throttle unit would be a good candidate for a contactless conversion using a Sacer sensor because you have no other throttle codes, meaning the control board is intact and working.

The XeModex website has a video on removal of the throttle and in Don's ETM Room there is a tutorial on replacement of the sensor. The sensors can be purchased on eBay for approximately $130USD.

[DavidsVolvo]

Thanks. In the meantime I checked the fuel injectors and all the coil packs. All seem good. I downloaded the ETM diagnostics chart and looked at the ETM removal and install videos from XeModex. Xemodex diagnosed and fixed my TCM perfectly. I trust them completely. Well, I am off to do more diagnostics. I'll report back in a few days.

[DavidsVolvo]

Hi precopster...I'm back with more info and questions. I went on the XeModex site and followed their ETM diagnosis chart. One major stopping point was that the chart said an ETM failure will never cause a misfire. I keep recording misfire codes 3502, 3522, 3503 and 3523 in addition to 9160 code. I can reset the misfire codes but NOT the 9160 Throttle unit internal fault, faulty signal code. Before I ignore XeModex about misfires not being related to a faulty ETM and proceed with the rest of the lengthy ETM diagnosis, are there any other potential causes for misfiring?

Here is my thought for your input...the feel of this engine for a misfire is not what I have experienced for a misfire in other cars I have driven. It's more of a very consistent rough running engine. It idles at normal rpm and accelerates at a normal rate. There is NO backfiring in the exhaust. When I took the timing belt cover off, there was a lot of antifreeze on the lower belt area and lower crank shaft cog from the very leaky radiator. (ya, I know. I was about to change the radiator when this problem occured)

Could the timing belt have slipped one cog on the crank? If this is the case, would these misfire faults show up?

Is there anything else that would make the engine run rough besides ETM, Coil packs, plugs and MAF? I believe all the components are fine except maybe the suspect ETM still.

[precopster]

Coolant on the lower crankshaft cog and lots of it? Sounds not good. Coolant is a slippery substance. It sounds more like the water pump has sprung a leak. If timing belt has slipped a couple of cogs misfires will be rife.

Time to check timing marks and whip out a compression tester to see if there's another problem.

[rspi]

When I took the timing belt cover off, there was a lot of antifreeze on the lower belt area and lower crank shaft cog from the very leaky radiator.

How would coolant from a bad radiator get into the timing belt area? Sounds like a water pump leak to me. How old is the water pump?

[DavidsVolvo]

If the leak in the radiator is on the passenger side midway up or higher where the plastic meets the aluminum, the wind from driving at highway speeds blows it across the belt area of the engine. The water pump checked out to be perfect and so was the timing belt position.

It's on to the compression check. BTW, what should the compression be on a 2.4 light turbo engine from 1999?

[precopster]

Good compression may vary from 155 to 180 psi for an LPT.

[erikv11]

It won't help with the coolant leak but: looking at your first post, checking the cap and rotor is the first thing that comes to mind regarding the misfires and if it hasn't been done yet then I would give it a look. E.g. is the rear cam seal popped out?

[DavidsVolvo]

1999 v70 volvos do not have distributors. They have coil packs on each spark plug. I know I need a new radiator, but if there is something real expensive tat is causing the misfire (e.g. ETM) then it may be going to the bone yard. I'm checking the compression now. Stay tuned...