Engine chugs after hot restart

[Breeves002]

Just don't be surprised when replacing the PCM leaves you with the same problems.

If it runs fine after a few seconds, I would just live with it...

[behlinla]

As long as the O2 sensors are functioning properly when the chugging occurs (did you ever check that?), then I would almost have to think it's the PCM because you've basically ruled out almost everything else. PCMs can have heat soak issues themselves if they have cracked solder joints. The poor connections might only exist in a specific temperature range. Crazy one minute and back to normal the next is the sort of thing you see when PCMs go bad.

Yes it's possible that the cause is something else besides the PCM, but it would take a lot more advanced diagnostics to be able to figure out what's wrong. Sometimes when you don't have access to these tools you have to take a guess with replacing the PCM after you've ruled out everything else you possibly can.

If you do replace the PCM, it would be interesting if you cracked it open and found any dull or cracked solder joints. If that's the case, it might be possible to repair it.

[3.0vulcan]

What do you think about this?


When you are completely frustrated with this issue, please do what was suggested by a senior mechanic by the name of Steve in Minnesota somewhere on the internet. The problem is related to the cooling system, and requires you to remove the radiator and/or the condenser for a full cleaning of the surface and fins. The radiator and condenser needs to be completely removed or provisions need to be made to thourghly flush out any accumulated dirt, cottonwood, foreign matter, ect., from the fin material. I for one was completely frustrated with this hot start issue on a 2002 Windstar with a 3.8L engine that would run terrible for 30 seconds to one minute after it was started following a hot soak of 10-20 minutes stopped while warm. The vehicle was tuned up with new plugs and wires, new coil pack, computer scan and reset, different fuel grade and supplier, you name it it was tried! This repair did correct the rough running after hot soak instantly from the time the cleaning was performed. I did remove the radiator and condenser(need to remove refrigerant and plug fittings) from the vehicle(I am an hvac tech/mechanic part time) so this was easier for me to do, but if you can't/do not want to remove the condenser, then it is imperative that provisions are made to make sure that all surfaces of the radiator and condenser can and will be completely flushed and cleaned thouroghly! I did spray all surfaces on both sides of the condenser and radiator with "Purple Power" cleaner available from my local Dollar General store. This "Purple Power" is similar to Castrol brand "Super Clean" but at a reduced price. These two cleaners have high amounts of cleaning power and worked extremely well for me in removing the dirt and crud that had accumulated in the condenser and radiator. Upon first look it does not appear that there is much stuff clogging up the fins in either the radiator or condenser, but when you start cleaning and flushing out you will be amazed with what comes running out I know I was! Once cleaning was completed I re-installed both radiator and condenser and refiled freon and anti-freeze, tested and never had another hot start issue to date! In retrospect I really didn't think this would cure the problem, but after trying everything else it did really work! Although the vehicle here is a Ford Windstar minivan, I have no doubt that this repair may help cure other vehicles ailed with this seamingly random hickup in drivability that is almost nevery re-producable for your local garage! For me I would like to thank Steve in Minnesota a master automotive technicial at a Ford dealarship for the advice to clean the radiator and condenser, it did work for me!

[3.0vulcan]

One more thing to add engine is in open loop when started so o2s are not

reading yet with temp about 185 and starts to smooth out slowly when

going into closed loop approx 15 seconds later

[behlinla]

In regards to the coolant system flush—how does your coolant look? Have you had a clogged heater core before? When was the last time the coolant was changed? Have you had any overheating issues?

If there is a lot of crud in the engine block, it can act as "insulation" and cause the engine block and combustion chambers to trap heat and end up being hotter than expected when the car is started, which will cause a hot rich condition. So there is some credence to that theory. The other contributing factor might be an out-of-range coolant temperature sensor. If it's reading too low, then the PCM will be adding too much fuel. Newer engines used cylinder head temperature sensors to avoid this problem.

So it's running rough, then it goes into closed loop, the fuel trims start at about +9, then the fuel trims come down and it smooths out? In other words, going into closed loop it what makes it stop running bad? Does the coolant temp change much during this sequence of events?

[3.0vulcan]

Originally Posted by behlinla

In regards to the coolant system flush—how does your coolant look? Have you had a clogged heater core before? When was the last time the coolant was changed? Have you had any overheating issues?

If there is a lot of crud in the engine block, it can act as "insulation" and cause the engine block and combustion chambers to trap heat and end up being hotter than expected when the car is started, which will cause a hot rich condition. So there is some credence to that theory. The other contributing factor might be an out-of-range coolant temperature sensor. If it's reading too low, then the PCM will be adding too much fuel. Newer engines used cylinder head temperature sensors to avoid this problem.

So it's running rough, then it goes into closed loop, the fuel trims start at about +9, then the fuel trims come down and it smooths out? In other words, going into closed loop it what makes it stop running bad? Does the coolant temp change much during this sequence of events?

I change the thermostat and coolant about every 3 years, the coolant

looks good, the car has never overhheated and the heater works great.

The coolant temperature sensor is new and seems to to be working

properly when comparing to the live data on my scan tool.

It seems to smooth out when going into closed loop but it might be a

coincidence.

I know i should just live with it. But now I have to know what the problem

is.

[Breeves002]

I could see how it would be a PCM heat soak problem. I don't think the closed loop is a coincidence. I think that it's showing that something is happening. It's an effect of the cause. Either PCM heat soak problem or some other heat soak issue. Maybe MAF?

So we have to think what changes from open to closed loop. Open loop reads from the MAF sensor to set fuel trims instead of O2 sensors like it does in closed loop. So I know you said you changed with a known good maf, but maybe try replacing it? Expensive though.

[behlinla]

Fuel trims are not typically used in open loop. They should show up as zero if you are watching them with a scan tool while in open loop.

It would be more correct to say the PCM uses the MAF and RPM information in open loop to attempt to obtain a predetermined fuel mixture. Closed loop adds the function of the O2 sensors to make fine adjustments or "trim" the mixture.

[Breeves002]

Oh I didn't realize fuel trims weren't used. Again, I learn something new every day. It makes sense though.

So what would cause it to chug in open loop?

[3.0vulcan]

Do you think a crank sensor or cam sensor could cause this problem? I know there either good or bad but maybe there something funny going on.