Q: Car misfires after distributor, rotors, plugs, plug wires replacements. 1999 GMC Savana 3500

asked by on September 09, 2016

I purchased my car from a public auction and then had my mechanic examine it. He told me that it was misfiring and should have a tune up. He changed the distributor cap, rotors, plugs, and plug wires. After those replacements, the car is still misfiring. Even though the check engine light is not on, he still hooked up the hand-held computer to the van but there was not any code. He had me drive the car for 30 minutes, he re-tested it, but no check engine light ever appeared. Now, he is speculating the it might be the fuel filter, fuel pump, intake manifold gasket, or something else. He also suggested that perhaps I should take my van to the muffler shop so that they can change the intake manifold gasket. He is a good mechanic and usually can spot the problem right off and fix it, but this one has him puzzled as to what the solution should be. I’m wondering if perhaps I should take the car to a dealership for a diagnostic. Before I spend more money on replacements, would you give me your assessment of the misfiring problem and how it can be fixed?

Although the person who serviced your vehicle the first time did not repair the issue, I think he might be correct about the fact that it could be an intake manifold gasket or a fuel pump issue.

You may want to consider having another mechanic look at the vehicle to get a second opinion on this. This inspection would include testing of the fuel pressure to determine whether or not it is within the specifications set by the manufacturer. If the fuel pressure is low, the fuel pump is very likely having an issue.

If the fuel pressure is within specification, I would recommend having a vacuum test performed on your vehicle to determine whether or not the vacuum level is within specification. If the vacuum level is low, the intake manifold gasket may be the issue. Another way to confirm the intake gasket issue would be spraying some brake cleaner around the area where the intake manifold connects to the engine. If the engine revs up when the brake cleaner is sprayed in a certain spot, the intake gasket is most likely the problem. Once the problem has been verified, the mechanic will be able to give you a list of parts that may be needed in order to resolve the misfiring issue.

Was this answer helpful?
The statements expressed above are only for informational purposes and should be independently verified. Please see our terms of service for more details

Get an instant quote for your car

Our certified mechanics come to you ・Backed by 12-month, 12,000-mile guarantee・Fair and transparent pricing

Get a quote

What others are asking

Car is shaking violently

Since you have listed a number of issues, there is no certain way to provide you with a definitive answer. It's highly unlikely that all your issues are rooted in one part or system. If the plugs are covered in...

My car will be in neutral but still stays at 1500 or 2000 rpms while driving

There are a number of things that can make a car jerk while you are cruising. Many of them would bring up a check engine light, but there are a few, like fuel pressure problems, that might not. With a...

Clunking when braking

This comes up often on this vehicle. It is caused by a loose part on the suspension. It is usually a bad ball joint or control arm bushing. When one of these parts fails, the suspension will move or shift...

Related articles

Symptoms of a Bad or Failing Brake Rotor/Disc
Common signs of faulty car brake rotors include noisy brakes, vibrations that can be felt through the pedal, and score marks on the rotor.
How Often Should the Fuel System Be Inspected?
Without Without fuel, an internal combustion engine will not run. For this reason, parts used in the fuel system are built for durability and can stand up to years of near-constant use. Some parts, like the fuel filter, exist to...
What Is the Purpose of Engine Gaskets?
Engine gaskets work as seals to maintain pressure, hold fluids, and prevent debris from entering the engine. Gaskets are vital for engine performance.