Car dies after starting on me

[daysshebs]

good morning matthew:

can you please help me?
i own 1989 740gl volvo
while i was driving car it would not go reg. speed, i stepped on gas n still would not p/u speed, then minute later i had to pull over bc car died on me. was towed to mechanic last week bc car starts then dies. mechanic replaced duel fuel pumps, still same problem. then he replaced timing belt n tensioner, same problem, then he just replaced 2 relays, still same problem. need help. my car never gave me this trouble i take good care of my car for 32 yrs now. (i bought it brand new back in 1988). ty

[pbierre]

The mechanic you took it to is not impressing me....a good Volvo mechanic uses tests to diagnose engine misfiring. Your guy just guesses and throws hardware at it, sticking the customer with his unproductive guesswork.

Find a Volvo engine expert who has VIDA (a computerized diagnostic tool specific to Volvos), and knows engines from the 1989 era.

There are too many components that can cause misfire to list here. These 3 things have to all come together perfectly in the cylinder for the firing of the power stroke:
• the fuel-air mixture delivered is in a narrow range where explosion will occur
• the spark is high quality and snaps at exactly the right time
• the cylinder is airtight (no leaks), so that the explosion drives the piston forcefully

There are many subsystems that cooperate to make this happen, and failure in any one component can foil it. A good Volvo mechanic knows how to systematically get to the root cause.