Engine missing on three cylinders

LUGNUT67

MEMBER
1986 CHEVROLET CORVETTE
5.7L
V8
2WD
MANUAL
27,000 MILES

The car was running okay when parked a few months ago. Now it is missing on at least three cylinders, number five, six and seven. Those are all in a row in the firing order, I changed the cap and rotor, even though they did not look bad. I checked for compression, and listened to the injectors, and checked the spark at the plugs. The plugs are new, and everything checks out okay. The computer was changed last year and everything had been running good before it was parked. Is there a sensor that could causing this? Or something like an EGR that would cause a vacuum leak?

Friday, March 10th, 2017 AT 12:38 PM

1 Reply

STEVE W.

MECHANIC
15,241 POSTS

Parking a vehicle for a few months can really kill them. If you have been running modern alcohol enhanced fuel it it I suspect that is the problem. It attacks the rubber used in older vehicles. It also cleans any dirt or rust in the fuel lines and plugs up filters and injector screens. The only real fix for this is to replace all of the rubber lines flush the rest of the lines (or replace them with stainless) replace the filter and pull the injectors and clean them.

However -
First test, fuel pressure and flow, plugged filter from dirt could cause multiple misfires.
Next test the resistance of each injector and do a simple injector flow test. https://www.2carpros.com/articles/how-to-test-a-fuel-injector
As you have already checked for spark and compression the fuel system is about the last item.
Test for a vacuum leak using either starting fluid, propane or water.
Good luck.

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Friday, March 10th, 2017 AT 4:35 PM