Hesitation when restarted hot

Trying to figure out what might be going on. I have an '86 3.2 with 21k miles. It is just excellent in every way except one.

It starts and runs beautifully from cold. When I start it warm or hot, it starts beautifully but it then will often run a bit rough, sound slightly off, and hesitate under power. It won't quite wind out. It feels almost like it's not running on all eight.

But why? If it were just that it ran poorly when hot, that might lead my thinking one way. But it runs great cold or hot..except when restarted from hot. This sucks. If I drive it somewhere it often runs badly all the way home.

Suggestions?

 

not really...but how about the fuel accumulator?
When the diaphragm is leaking the fuel pressure may sink and with the engine hot vapor lock may occur.
Another thingy to look at may be the cold start fuel valve, does it shut off after the right time, is it dripping?
Just some thoughts,

cheers

braq

 

What version? US or euro or euro converted to US or?

(PS Is your Profile out-of-date since it shows a 308-2Vi?)

 

How old are the ignition wires? As they heat up it loses the dielectric insulation strength and the spark "escapes" out the insulator
if they are old it gets worse and the car will run poorly when hot

I would say to touch them but it might give you a jolt

 

This was my thought, heat soak could be bringing up the temp enough to cause an open. But then wouldn't driving it cool it down?

I'd probably still start with the wires and the extenders.

Maybe when it's hot, do the fire it up in the dark and look at the engine bay to see if you can see arcing. Not conclusive unless you see it

 

Yup, profile is out of date. Used to have a 308.

So why would it be different after restart than when just running hot. I can drive for an hour and it will run great. When I shut down and restart before it's fully cooked (like when returning home from a restaurant or something) it will misbehave -- but only then.

Cold start system seems like a likely bet to me. How best to test?

 

Agree that that seems a little strange.

But you didn't answer the version question -- US or euro or a euro converted for US importation?

 

uhm cold start is only for COLD start .....that is not what you are describing

so only after RE - start when hot?

1) could still be wires you have not answered how old they are, trust me out the box I had a bad extender
2) accumulator
3) cis pressure
4) fuel pump relays
5) ignition module

possible solutions:
1) while off unplug and visually check extenders for any black marks (that would indicate the extender going bad) twist wire in you finger if microcracks or "whitening" the insulation is going bad) grab hold of couple wires.... just kidding..but seriously while running unplug one wire at a time and see if that makes the engine reduce idle,
2) take off the fuel return hose from the accumulator if its wet bad accumulator
3) take off the air filter housing and gently touch the plenum there should be pressure for at least 4 minutes (if not there are other issues to track down), unplug the blue safety plug and check that the fuel pump motor runs when you push harder to open the plenum
4) clean the relays contacts possibly replace
5) clean contacts and grounds

 

.

Sounds like a sensor problem -- Mass Air Sensor and/or MAP.

 

Steve: sorry. U.S. Model.

 

Getting the CIS pressures checked would be a good place to start for diagnosis (along with checking the ignition harness as previously suggested) .

I have had "hesitation" when running and usually when spooling down from a high speed run (er, umm....where legal of course...!). Also loss of power and "e-awing" when hot and pulling away in low gear. All cured when CIS checked and adjusted properly.

 

The first thing to do is confirm/deny if the frequency valve (sometimes also called the metering valve) is working/buzzing when the engine is running well, but maybe not working/buzzing when running poorly (you can do this just by touching it to feel if it is vibrataing). If that's not the trouble, then try unplugging the single wire from the O2 sensor during warm running -- if it also runs poorly (warm) with the O2 sensor unplugged = that virtually confirms that either it's not tweaked up properly or the various pressures in the CIS system have shifted since it was last tweaked up correctly and need to be checked/fixed as 308mon suggested. Good Hunting!

 

The mystery here is why this all happens only upon restart. I understand that the cold start system is supposed to be active only for a cold start, but I was thinking it might be malfunctioning but nevertheless active upon starting. I had an issue with that setup in my old 308, although it led to high idle not this kind of rough running.

I do not think it's the extenders. My friend and mechanic (also an Fchatter) checked those out and found them to be in good condition. He couldn't get the car to act up while he had it so he wasn't able to diagnose the problem. It's acting up again now. Some of the things on this thread are certainly worth investigating. Thanks for all the advice!