Contour Enthusiasts Group Archives Forums General Troubleshooting Stumbling/bogging when engine cold

Problem happens before the engine is fully warmed. After warm, no sign of this problem.

The behavior occurs whenever I try to accelerate (pretty much any gear) anything more than very mildly.

Example, engine cold, accelerate half throttle in 2nd gear starting at 1500RPM. Engine begins bucking/kicking/surging and sounds like it's going to stall if I keep it up. It gets pretty violent.

If I left off the throttle slightly (still bucking slightly) and keep the RPMs climbing, at about 2700RPM the behavior stops and it totally smooths out. It's almost like it hits the point where the secondaries open up and that solves the problem.

So...a quick questions about the secondaries. I know they open under WOT, but do they also open if you happen to accelerate lightly and happen to reach a high enough RPM??

I've just recently done the following things:

Replaced both O2 sensors
Cleaned the EGR passages and TB
Verified EGR operation
Replaced plug wires
Replaced plugs AutoLight double plat. .054"
Replaced fuel filter
Air filter is clean

I've been meaning to test the fuel pump pressure, but haven't gotten around to it yet.

Chris
'95 SE MTX 107Kmi.

secondaries dont have much of anything to do with this problem, since you have a 95. You dont have an IMRC box, hentz your secondaries are vaccume operated. As for them opening, they only open when you pass 4K rpm's. At which point your engine knows you need to GO GO GO so it sends your gas mileage down the drain and lets the engine push hard. THIS sounds a hell of a lot like a misfire issue, like sometime wasnt installed correctly when you were changing your plugs and wires. Do you get a CEL or any kind when the bucking occurs?

If your Secondaries werent opening or not functioning correctly, the only time you would feel it is if you ever passed 4K rpm's. Not if you just gun the throttle for a few seconds.

Clean the MAF. Put Heet in gas. Test for plugged cat by removing O2 sensor.


Edit. The best way to test if the exhaust is blocked is to take out the O2 sensor (disconnect battery first), then see if the car drives better. That gives the exhaust a place to exit. Remember to put back the O2 sensor after the test. I think the O2 sensor can be removed with a 22 mm crescent wrench (I used a 7/8 inch crescent wrench when I removed mine to install MILeliminators).


MAF
http://www.contour.org/mods/mods.php?s=howto&displayid=36

Although warmup related problems are usually related to vacuum leaks or the ECT, yes the secondaries can also cause this and it is worse when it gets cool out. The secondaries are strictly RPM operated.

Look under the throttle body for the secondary shaft ends and the linkage bars both between them and down to the vacuum operated dashpot. Have someone start the engine. they should close (they will even close just when the ignition is turned on if there is still vacuum in the reservoir). If they do not, test for vacuum going to the dashpot at idle. No vacuum means the IMRC vacuum solenoid bolted to a plate on the back of the rear head is bad.

Sometimes the system is working except the plastic retainers have broken and the linkage has fallen apart.

BTW if you were wondering, the secondaries are closed at low RPM to speed up intake runner air velocity and both improve fuel mixing and improve cylinder stuffing as the intake valves close.

Thanks for some good suggestions/responses.

A couple of other things that I thought of that I meant to ask:

1) What sort of engine behavior might I see if I had a fuel injector going bad or not having a good spray pattern? Could it give me these symptoms:

2) How do coil packs usually fail? Do they quickly fail one or more plugs or can they slowly die?

Chris

Check your DPFE sensor. Try unplugging it if it goes away replace with a new sensor. Should be an easy test. It is the silver box that has two hoses coming out of it and a connector attached to it on the driver's side rear head.