Car wont start and Compression Testing

Damians850 · Post by **Damians850** » 12 Nov 2025, 20:41

my 1994 2.4 volvo 850 wont start. we have spark and fuel. just did a compression test and these are the results starting from left to right

piston 1. 75 cold (150 with some oil poured down)
piston 2. 91-98 cold ( 120 with oil)
piston 3. 110 cold (115 with oil)
piston 4. 71-78 cold (155 with oil)
Piston 5 . 95-100 cold (145 with oil)

do these numbers seem okay what are your thoughts? Timing belt might have slipped a tooth.

Post by **Grantkat** » 13 Nov 2025, 06:59

There are 2 factors to consider: first compression and as I understand it you want to see somewhere between 120 and 175. Just as important is consistency. You want to see consistent compression across the cylinders and no more than 10-15% variation.

You suspect timing slip - what makes you suspect and and was there an incident or issue that started this? In a case like this it is super helpful to describe to the best of your ability what happened between "it was running fine" and it wont start. that might help narrow it down.

Damians850 · Post by **Damians850** » 13 Nov 2025, 07:52

Car was running and then next time i went to start it it idled rough for a min before stalling. car wouldnt start after that. i checked the codes and they read that i had a cam position sensor fault but i checked the sensor itself and its working. if the belt slips it can also show the same code if the timing is off.

The issues im now dealing with is if the timing is off, my cam gears dont have any notches on them indicating where they should allign. any other way i can align the gears if the sprockets itself have no markings?

Post by **volvolugnut** » 13 Nov 2025, 08:29

First, some more background information will be helpful.
How many miles on this engine?
What service and maintenance has been done and at what mileage?
How long between running and next time started with poor idle and stall? Days, weeks or months?
Current information needed.
Have you confirmed you have fuel to the injectors?
Have you confirmed you have spark at the plugs?
Have you confirmed you have a strong battery with about 12.5 volts at rest?
How did you test the cam position sensor?

I think if you are getting these sort of compression readings your valve timing is not bad off if any. You likely have cam marks but they are small and hard to see. These marks are not at top dead center if that is where you are looking.

volvolugnut

Damians850 · Post by **Damians850** » 13 Nov 2025, 08:48

288,000km on the car. yes we have tested for fuel and spark. battery is strong, cam sensor has been tested, oil done every 5km. around 12hrs since it was running fine to when it idled really rough then stalled and wouldnt start again.

Not sure last time previous owner replaced the timing belt and if they used aftermarket cam gears but unfortuntaly there is no markings at all. have spent lots of time trying to identify any sort of markings but nothing can be found. any other ways to allign the gears without markings?

Post by **volvolugnut** » 13 Nov 2025, 09:04

You have done all the right things. I have no other advice.
volvolugnut

Post by **Sveedy** » 13 Nov 2025, 12:29

Look online for a picture of how the cam gears should look when properly aligned, relative to their mounting bolts. As I recall one of the gears 3 bolts pattern make a basic triangle, and the other an upside down triangle. Then you might be able to see exactly where the punch marks are supposed to be. Don't know if the gears can be installed either way, but maybe the marks are on the back sides of the gears.

Post by **Grantkat** » 13 Nov 2025, 13:46

This will be a PIA, but check (as best as possible) the back side of the gear(s) for a mark.

Also This may seem a bit of a waste, but check both sides when its dark (lights off if in garage) and use a flashlight with a focused beam.
I can tell you from experience that often ambient light coming in from the sun, overhead lights etc can wash out a slight marking. More than once looking with a flashlight in the dark, and viola there it is....

Post by **misha** » 13 Nov 2025, 13:57

Even if they are aftermarket,which would be odd,they must have notches for timing alignment.

Otherwise...how would anybody allign timing belt without them?

2 teeth off is a limit...3 teeth off is a game over.

Look more closely...they are there.

Btw...with that compression....engine is long gone.

Post by **scot850** » 14 Nov 2025, 15:26

There is something off with those compression numbers. Misha may well be right. With numbers that low it may be the rings are toast.

Adding oil helps to help confirm that the piston rings are an issue, as the readings go way up it is a ring issue. No change it is a valve issue.

However, there is another possibility. It is called lawnmower syndrome. This happens when the bores get washed down with fuel when you crank the motor over a lot without is starting.

I would look at on-line resources to make sure you can find the timing marks correctly. If you can't, then you have misaligned the timing. The crank pulley mark is hard to recognize, so do look at pictures so you can recognize the marks on the crank.

Get the timing correct. Then finally, add a teaspoon of oil to each cylinder and then try to start the car. If it is lawnmower syndrome, then once the car is running it should go back to normal once it is hot and had a run.

Neil.