I have a 1991 240 sedan with 132K miles. The car has began to start hard and occasionally back fire through the intake manifold upon starting. Once started and warm the car can be restarted and will start normally. Also when warm the car runs normally. The RPM at idle is 1200. The last major maintenance was a timing belt at done at 125K miles. I did not replace the belt tensioner when I put the the timing belt in.

Thanks any help would be appreciated.
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1983 242 GLT / 1991 244 / 1993 245 / 1999 v70

Also, please see and perform the:
http://www.brickboard.com/FAQ/700-900/EngineOBDCodes.htm

Diagnose and resolve your air intake system issues. Of note is the fuel pressure rail valve diaphragm leaking through the attached vacuum hose into the air intake port (manifold).

Got EGR as my German market 1991 240 sedan does? Inspect that system also. If EGR equipped, OBD-1 socket six (ignition) test.

Indeed, if recently replaced, suspect the timing belt alignment. Always replace the timing belt tensioner every 100k miles (every second timing belt) with OEM; cheapest at Tasca Volvo parts + shipping.

And within a few miles, and every 100 or less miles, reset the timing belt tension using the procedure in your blue Bentley Volvo 240 Service Bible (you DO have one, yeah?). There after, I reset timing belt tension every oil change. I also do the "twist the crank harmonic balancer pulley" slightly counter clockwise as you face the engine front to expose the tensioner pulley to all slack in the belt. Too much slack shortens belt life.

Grumpy Button
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Gland Nut Strikes AGAIN!!!!!

Kitty,

Don't you wish Jarrod would highlight threads with dates < (sysdate - 365) so these informative and well-composed replies we make are not exercises in self - uh - you know what I be sayin'.
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Art Benstein near Baltimore

Waste of time.

First thought is too much air causing incomplete combustion of the improper mixtures across the cylinders.

This can be air leaking in behind the AMM or upon cranking the engine which can be from using he gas pedal. That is a no, no!

The 1200 rpm idle is way to high which flops back to the too much air again and a stuck Idle Air Control motor, if it does it even after warmed up then this valve will act like the foot on the gas no, no. It is located in the bypass air line under the intake manifold.

Next part to incomplete combustion would be improper fuel spray due to lack of the fuel rail being full and the injectors not atomizing correctly. Backfiring is latent fuel vapors burning back up in the intake runners around the intake valves.

So if it runs good the rest of the time, the timing belt idea can be eliminated for the most part in my opinion.

Compare thoughts from other posters and good luck.
Phil

"The 1200 rpm idle is way to high which flops back to the too much air again and a stuck Idle Air Control motor, if it does it even after warmed up then this valve will act like the foot on the gas no, no."

Let's start with the idle. Is the throttle body clean, the idle stop, cable and throttle switch adjusted properly? Ham-fisted mechanics, especially those that grew up on carbs will adjust the throttle cable or idle stop to create some semblance of idle instead of just cleaning the TB and looking for vac leaks.

Next is to find vac leaks. The big ones are the accordion hose (usually hidden on the bottom), brake booster hose, and IAC hose. After that the smaller hoses, including the one going intot he cabin for the HVAC controls) are all suspect. Finally, the intact manifold gasket.

I cleaned the throttle body and looked for air leaks. The throttle body was a mess, no air leaks were found. The idle was still fast. I am beginning to think that when I put in the timing belt it is a tooth off. I will have to purchase a timing light and check the timing. Still working on it.

Thanks



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1983 242 GLT / 1991 244 / 1993 245 / 1999 v70

"I will have to purchase a timing light and check the timing."

Better to borrow it for your '91. The LH 2.4 system decides timing. You can't adjust it. However, you could buy it for your '83 GLT.
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1980 245 Canadian B21A with SU carb, M46 trans, 3:31 dif, in Brampton, Ont.

Trev is right. Nothing the OP could have messed up on the timing belt would change the ignition timing, as measured with a timing light. But that does not rule out improper alignment of the belt.

The belt controls valve timing at the cam sprocket -- a possible explanation for the back fire and idle problem. It also controls the selection of a plug to fire at the I-shaft sprocket; that one has to line up to make sure the path from the coil to the correct spark plug is complete regardless of where the computer puts the ignition timing.
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Art Benstein near Baltimore

With her marriage she got a new name and a dress.

I am having the Same issue with my 1979 245.
It started as a hard start issue that just got worse and worse. fuel economy plummeted. Finally the Hard start would take 20 times then it would start and would restart fairly easily after warming up. then the hard starts began backfiring through the intake and it stopped starting altogether. now she just cranks and backfires.
I have not been able to solve this issue.

Like I said, there are three parts to the throttle body issue. Unless the car has been with you for a very long time and this is a sudden increase in idle, you have to check the other two...is the plate coming to rest with the barest sliver of clearance and is the throttle switch clicking as it comes to rest on the stop with a tiny bit of slack in the throttle cable.