S4s runnning rough/stutters

[kabdulla]

Hi all, my 1995 S4s is running rough - specifically, on acceleration, it stutters (in any gear).  This happens under light acceleration or under hard acceleration (i.e. seems to be independent of the turbos).  One other (strange) clue is that for the first 30 minutes of driving or so, it accelerates perfectly. After about 30 min however, this stuttering begins.  

 

So far, I have replaced the spark plug suspecting an ignition problem of some sort.  Seems to me that its either an ignition problem or a fuel delivery problem (that is temperature dependent)?

 

Any other suggestions?

 

thank you!

Karim

[mr.oogieboogie]

Check the coil packs and clean the connectors. As a bad earth is common as well as water getting in. Then check the fuel pressure. Coukd be the pump on the way out

[Vulcan Grey]

I had a spark plug wire issue that was similar, replaced all the lead wires.

 

It could be all of the above.  Start with the easy stuff.

 

Inspect the plug wire, the coil packs, the grounds.  Verify spark at each plug, Ohm out the plug wires. 

If it is only on certain cylinders, for example 1&4 and 2&3 are batch fired, where spark and fuel are activated on both cylinders in the pair at the SAME time as the other in the pair.

 

That way if you can tell if it is on a pair, it could be the coil pack not providing spark to both, or it could be 2 bad plugs/leads, or it could be the driver in the ECU.

 

So if you have a pair that isn't working, you have to swap plugs, leads, or injectors around in order to figure out if it is the part, or the circuit that is at fault.

 

I once had 2 injectors that wouldn't fire, but they were on 2&3, so I couldn't tell if it was the injector driver.  I switched the injectors to 1&4, and the problem followed. but you can't tell if it was only one bad injector taking out it's paired injector, so I swaped them again to 1&2, and the problem followed both injectors to 1&2, so I knew I had 2 bad injectors.

 

If you can't tell which cylinders are the problem, do this.

 

Start the car and let it idle.

Disconnect the IAC idle control valve electrical connector.

Look at the RPM's

remove one spark plug wire at a time and note how many RPM's it drops.

do that for each cylinder.

if one or more cylinders doesn't change the RPM's when you remove the plug, then that is the bad cylinder.

 

 

If you have good spark on all 4, then I would pull the fuel rail, complete with injectors clipped in the top, lay some paper towel under the injectors.  Crank the engine and see if you get wet spots under all 4 injectors.  Swap them around if more than one is dry.

 

Also check fuel pressure. The pressure should rise with boost.

[iainskea]

Best answers above. Also, check for a dirty fuel filter.

Iain

[kabdulla]

Peter, Travis, Lain, thank you very much for the great tips! I will keep you informed of my progress, although admittedly, it may take me some time to take the steps suggested! :-)

Karim

[mr.oogieboogie]

The bottom bolts on the coil pack earth them the are 5.5mm and can be tricky to access. I had to re tap the backing plate they screw on to. I would so run an additional earth that links both bottom bolts then to the chassis. My money is on the coil pack. You can replace them with msd ones cant remember the part number. The issue you have sounds like when my coil pack got water in.

All the best

[fflyingdog]

Might also be worth looking at the Lambda sensor,if I remember correctly it doesn't come in to work untill the car is up to running temp,am at work so will stand corrected if speaking rubbish.

 

 Nick S4s

[kabdulla]

Thanks again guys - great tips!

 

-Karim

[JayTwo]

Did you work this one out Karim?

I seem to have the same problem on my carb turbo - the 'delay' before anything's wrong is perplexing, it feels much longer than the warm-up time I perceive for the major components. For me, stopping the car briefly (to get fuel for example) often brings it on early or again though.

I can't keep calling it her moodiness forever :-D

[kabdulla]

Actually Jay, I should be receiving a new O2 sensor tomorrow from JAE - I will publish my findings after I put it in.  I also purchased a new set of plug wires just for good measure.  I'm trying the easy stuff first!

[kabdulla]

Guys, here's an update - I installed the new O2 sensor yesterday and the problem persists.  Specifically, during the first 15 minutes of driving, the car is perfect.  Then after 15min, the stuttering/hesitation begins.  And also at this time, there is a noticeable fuel smell in the cabin.  While the fuel smell could be the hoses and/or the tanks, it seems like too much of a coincidence that the fuel smell starts at about the same time the car starts stuttering - seems to be fuel is going unburned. Next I will replace the plug wires (spark plugs themselves are new), but its looking more likely that its the coil pack.

[kabdulla]

Ok, here's the latest -

 

Recap:

1) Installed new spark plugs - no change

2) installed new O2 sensor - no change

 

New Info:

3) Installed new set of plug wires - stuttering issue is resolved!! And furthermore, fuel smell in cabin is gone also.  Here are some resistance results on the plug wires for both the old set and the new set:

===OLD===

- Cyl #1: infinite ohms (i.e. clearly a bad plug wire)

- Cyl #2: 14.7 kohms

- Cyl #3: 12.3 kohms

- Cyl #4: 11.7 kohms

 

===NEW===

- Cyl #1: 2.08 kohms

- Cyl #2: 1.93 kohms

- Cyl #3: 1.68 kohms

- Cyl #4: 1.619 kohms

 

4) Purchased two new MSD 8224 coil packs - even with the above issue resolved, I will still install these for good measure ($54 each)

 

HOWEVER (why is there always a "but"?!), during my test drive, I noticed the following:

1) The turbo waste gate "hisss" was much louder than before,

2) I was not getting full boost pressure (seemed to be limited to 0.5 bar according to the boost pressure gauge)

 

Any thoughts?

[Vulcan Grey]

It's possible that you have a boost leak from one of the silicone hoses.

Otherwise it is usually either the coolant temp is too low/high, or the ecu detected a lean condition and is restricting boost.

The lean condition usually allows boost once, and then not again for 5 min, and the engine will buck and possibly back fire.

If yours isn't doing that, then it is probably coolant temp, which may or may not match the temp shown on the dash, since the sensors are different. You'll need to cross check using freescan.

[kabdulla]

Thanks Travis.  I have not seen the symptoms related to the lean condition you describe.  For the coolant temp, I will need to get ahold of a freescan and check.

 

For the boost leak theory, any chance someone can post a picture identifying the silicon hoses to check for the boost leak?

 

-Karim

[Vulcan Grey]

The boost leaks from the 2 pink hoses between the turbo-> chargecooler box->intake manifold plenum.  Check the 4 hose clamps and make sure they haven't slipped off.

 

[kabdulla]

Perfect Travis - thank you!

 

-Karim

[rossvm]

As a lotus technician I would suggest you replace the temperature sender for the ecu. This is the one under the plenum in the inlet manifold not the one in the waterpump which is just for the gauge. That would be where I would start as a faulty sender unot will play havoc with the fuel mixture controlled by the ecu. Cheap and easy to do. If you do it with the engine cold and do not open the rad cap you should not lose much water if you are quick and so reducing the need to bleed the cooling system but I would probably bleed it just to be sure.

[kabdulla]

That is great information - thank you!  If anyone has any tips/lessons learned on replacing the temperature sender for the ecu, I am all ears.  I will order from JAE asap!  

 

Aside note - I am already in new territory as far as doing any of my own work on the esprit - I can almost hear it screaming "ouch! what are you doing?!" everytime I poke around in the engine bay!

[Vulcan Grey]

I agree you should check the temperature sensor, but don't replace it just yet.  It is easy enough to verify whether it is working or not.

 

A coolant temperature sensor out of range will cause the ECU to limit boost, but it won't make the noise you were hearing.

 

You need to get freescan and compare the dash coolant temp to the ECU coolant temp.

You can also measure the resistance of the coolant temperature sensor while placing it in water at various temperatures.

 

Not to mention that the sensor may be fine, and it is a stuck thermostat that is actually causing the coolant temperature to be low/high and causing the ECU to reduce boost.

[rossvm]

Very simple and very common fault. Based on the fact it runs fine at first when cold but not when hot would be the reason I am swayed towards the temp sender. It may also be worth checking the setting of the throttle position sensor as if not correct can also cause problems.

[kabdulla]

Thanks Travis - 

 

Turns out the increased hiss sound was a false symptom.  I had the engine cover off during my test drive and I guess I was not used to hearing everything that I was hearing since I typically drive with the engine cover on. Once I put the engine cover back on, it sounded "normal". 

 

So the only valid symptom currently is the less than full boost.  Since I am getting "some" boost (around 0.4-0.5 bar according to the gauge), I believe there is no mechanical blockage (which was the case several years ago when my catalytic converter broke apart).

 

The one question I do have is wouldn't the Check Engine Light come on if the ECU was limiting my boost?

[kabdulla]

Actually, the symptom that was dependent on temperature was the stuttering (the original purpose of my post). The stuttering issue was solved with a new plug wires.  The current boost being limited to 0.4-0.5 bar is constant (i.e. does not behave differently when the car is cold vs. warm).

 

TPS is another good place to look - thanks for the tip.

[rossvm]

The smell of fuel in the cabin is often one of the following two things though not limited to them. Given the age of the car it is worth checking the condition of the fuel tank vent pipes. These run up the channel just above the 1/4 window over the bulkhead and down the other 1/4 window. They are clear although by now probably yellow and about 16mm in diameter. They do perish and split over time. If split they should be replaced. The other possibilty is corrosion on the top of the fuel tanks. This results in the smell of fuel being most noticeable when tanks are full.

Is the boost low all the time or just at first as full boost should not be available until the ecu recognises that full operating temperature has been reached

Sorry trying to read the forums on my phone but small screen and old eyes make it tricky missed that the original issue was resolved

[jonwat]

The one question I do have is wouldn't the Check Engine Light come on if the ECU was limiting my boost?

Does the CEL come on with the ignition & extinguish when you start the engine?

If not then the bulb has gone & that will limit the boost :-)

[Vulcan Grey]

Thanks Travis - 

 

Turns out the increased hiss sound was a false symptom.  I had the engine cover off during my test drive and I guess I was not used to hearing everything that I was hearing since I typically drive with the engine cover on. Once I put the engine cover back on, it sounded "normal". 

 

So the only valid symptom currently is the less than full boost.  Since I am getting "some" boost (around 0.4-0.5 bar according to the gauge), I believe there is no mechanical blockage (which was the case several years ago when my catalytic converter broke apart).

 

The one question I do have is wouldn't the Check Engine Light come on if the ECU was limiting my boost?

 

No the CEL will not come on for the boost being limited due to low coolant temp or even a lean condition in my experience.

 

As Rossvm mentioned, the sources of the fuel smell need to be checked out.  There is one more to add to the list.  The charcoal canister purges into the front side of the intake manifold near the thermostat. There is also a one way valve there. Check for splits at that hose and barb into the manifold and make sure the one way valve is working.  Follow the hoses back to the charcoal canister under the coolant header tank.