Hesitation at idle & accelleration only

[Dave G]

91 Festiva L, EFI, 5 speed, totally stock. When I first got the car about 3 thousand miles ago, it would sort of "buck" or missfire slightly sometimes during heavy accelleration. Has gotten steadilly worse. Now it does it all the time during idle, and all the time during heavy accelleration. Runs great when cruising steady or gently accellerating. I've replaced the air filter, cap, rotor, and plugs recently (before it started getting bad), but am pretty sure doing this did not cause the problem because it ran fine for some weeks after that.

What's the most likely problem?

[Tom]

The vacuum advance on the outside of the distributor has two hoses going to it, if they are loose or bad you lose vacuum and that can cause this, any vacuum leak can cause this.

My step one in this situation is always to put the yellow bottle of heat for 99 cents in the gas tank, one drop or less of moisture, summer or winter can cause this.

Step two replace the fuel filter. It also can cause this.

All these things need done once or twice a year anyway and cost little.

Half the cars in the junk yard wouldn't be there if these steps were taken.

My 89 carbonated was doing this so bad the guy that had it sold it to me for $150, it's a one owner with 168,000 on it.

Several mechanics and he and then me worked on this dozens of times.

I finally concluded that it was fuel not getting to the fuel pump. I took the fuel filter off on the lower firewall and then took the short hose off that goes to the fuel tank line and replaced it with an 18 inch hose, I then loosened the gas cap and blew with my mouth on the new rubber fuel hose, it blew hard at first and then let loose right away and blew easy. I blew some more and now it was a easy blow. I kept that long hose on and put it back together, it finally runs perfect. If it does it again I can just unhook the fuel filter and blow. The gas Gage doesn't work properly and I think he ran out of gas and put some dirty fuel from an old can and got something in the gas tank that gets in the hole that feeds the fuel line. I could take the tank off and shake it around and dump it and probably see what it is but as long as it works and I have an easy fix I will wait on that.

[festivaWES]

i don't think any of the EFI models have vacuum advance on the disty. My bet it is in your fuel system. Clogged injectors/filter, pump maybe going out.

[darkdan]

My was doing something similar at idle.

The engine would "loop" and sometimes die.

Turned out the fuel pressure regulator was really bad. It was allowing fuel to go into the vacuum hose somehow. I don't get it either.

[Dave G]

I seem to have fixed it! The plastic air plenum gizmo was not fully home on the throttle body. Loosened everything, pushed it in and tightened everything up. Hasn't coughed since then!

[Tom]

What is that thing, do I have one on my carborated, this may be my problem, my doesn't just cough and miss when I step on the gas, it coughs and misses so bad I can't drive fifty feet.

[FestYboy]

^^

no you don't have that on your '88, what you should do is replace your filter (it sits on the firewall) and splice in a fuel pressure gauge betweent eh pump and carb. it should read 2.5-4.5 psi. also make sure your accelerator pump and jet are opperating properly. do this by removing the air filter lid and look straight down the carb. have someone step hard on the gas and look for a sharp stream of gas to shoot out the inside wall of the barrel. NOTE: do this with the engine OFF!!!! another thing you can do is make sure the vac advance diaphram is working properly (the arm should move when reving the engine) SOMETIMES, the coil can't put out enough juice under load to make a spark, you'll need an inline spark tester to check this.

[Tom]

OK, I'll try these, thanks.

[Dave G]

I seem to have fixed it! The plastic air plenum gizmo was not fully home on the throttle body. Loosened everything, pushed it in and tightened everything up. Hasn't coughed since then!

Spoke too soon - started screwing up again. Soooooo, started looking for other problems. In examining the distributor cap, I noticed the poles were getting burnt way up on the flat of the cutout, not down where they are supposed to. And the rotor was getting burnt on top, not on the edge. Pulled the distributor and compared it to the one from Karl's old engine. On the other one, that plastic cap that goes under the distributor cap had an edge about 2 1/2 times thicker than the other - so the distributor cap was spaced out away from the distributor more. With it too close (as on the problem car), that would explain the "too high" burn pattern. So anyway, I swapped distributors completely, and the problem is gone. Oh happy day