The first thread was really disorganized and so I thought I would make a new thread with everything updated so its easily read and hopefully I can have somebody figure out what I should do next....

The misfire is random and inconsistent. There is no correlation to how hard it misfires. The misfires can only be felt at idle, and there are no problems accelerating at all. Car will accelerate all the way to the red-line at 6200rpm. Car shifts great and the condition of the engine is very clean. I have 80k miles on the car right now.

Here's my compression rates:
Parts replaced/steps done so far

• OVP
• Coolant Temperature Sensor (checked and ECU adjusted accordingly)
• Voltage Regulator
• Injector's+Seals (previous owner)
• New Fuses
• Non-Resistor OEM Bosch H9DCO's
• New Bosch Ignition Wires (Misfires were now not as strong, but still present)
• Distributor+Cap
• Fuel Filter
• Valve Stem Seals
• Breather Hoses
• Fuel Distributor
• Ignition Coil
• Fuel Pressure Regulator
• O2 sensor
• EHA Valve
• --Checked for Vacuum Leaks with solvent (also by 3 Indy's)
  -----
• I have taken the car to three separate Mercedes Indy's in California and none of them could tell me what was wrong so far.

Exhaust smells normal. I sprayed WD-40 around the injector's to test for leaks, but there was no change in engine speed.

We have set the duty cycle/mixture correctly ourselves, and by 2 indy's.

What's next to test for?

Here's the condition of the engine:

 

What is the status of the EZL? I can't see the vacuum line attached to it.

 

I haven't touched it. Is there a way to test it?

 

I guess I would start by pulling off the vacuum line, plugging it, and seeing if it makes a difference. Does yours have a check engine light?

 

Yes it does, and no its not on.

 

So the car thinks there's nothing wrong? No codes? That's odd... I recalled that I had this exact symptom with a '76 Cadillac Seville. It had the 350 cid fuel injected V-8. It idled rough but as soon as I touched the gas it was smooth. If I closed down the idle air valve it would smooth out. I never did resolve it and it didn't bother me that much.

Have you verified that the seal is good around the cold start valve AND the cold start valve is not seeping/leaking fuel into the manifold while running? I'd pull the valve while the engine is running and quickly cover the hole in the manifold so as not to kill the engine, and look for leaks or dripping. Be careful not to start a fire by getting gas on the manifold.

 

The error codes that the Indy pulled was for Altitude sensor and coolant temp sensor....The altitude sensor can't do this can it? And also the coolant temp is fine because he plugged this metal block into it and the engine increased the rpm's accordingly (this is why he said the ECU is fine otherwise it would not have adjusted)

I have not checked/touched the cold start valve at all. I don't have any problems starting the car when its cold. I'll check for leaks though.

 

The cold start valve is pressurized at all times when the fuel pump is running. If it has a piece of crud in it keeping it from shutting off completely it will drip or spray fuel into the manifold all the time. This will not affect cold starting but will make for a rich and rough idle that the EHA will try to compensate for. I would check it out right away. If you pull the valve and disconnect the wire there should never be a drop of fuel that comes from it when the engine is running.

 

If the coolent temp is fine and its drops a coolent temp code then the coolent temp sensor is bad.
Two bad sensors might be a wiring (ground) problem.

 

Would you recommend getting it replaced or is there any other way to test it?
My coolant temperature is fine.

Also, I was thinking and I don't know if this has any possible problem, but my gas cap has a lot of pressure when I release it to fill her up. There is a pretty distinct pressure release. Is this normal or ??

 

Well the cold start valve isn't leaking. Check that off the list.

Any thoughts about Temperature Sensor and the pressure release at the gas cap?

 

You indicate a misfire....is it truly a misfire ( which would be primary ignition related ) or an erratic idle with the engine occasionally "missing"???

You've done all the main things, but sometimes the obvious is not considered.
You have a few small vacuum hoses which become brittle and crack....did you mechanic do a full vacuum leak test?

Also you might want to check the idle speed air hose for leaks along with the airguide housing ( rubber boot between the mixture control unit and throttle body for leaks

This area is usually ignored as it is hidden under the mixture control unit.
You may be able to perform a smoke test to detect leaks in this area.

 

We have changed the all the idle hoses. It misses all the time, but can only be "felt" at idle as when the engine speed increases you can't feel it. The car is as smooth as can be accelerating. No problems at all. It just misses at idle.

We need to do a leak down test next when I get the time. I'm going to buy the gauge and do it myself.
The best we have done to check vac leaks is just using solvent (the 3 other indy's did the same).

What are the possibilities of bad injectors? The previous owners showed us the receipt that they were done....but should I trust that it was done correctly?

Also, what is this smoke test you speak of?

 

It's a low pressure test using a smoke tracer.
This is typical equipment used:

http://www.redlinedetection.com/faq.htm

 

$995 :-O

The temperature suddenly shot up today from 70F to 85F in southern Cali and the misfires are noticeable worser today.

Could this give any further indication? What about this coolant temperature sensor code? Could it have any relation to the misfires even though my temperature readout on the dash is normal?

 

Ps2co,

The outside air temp climbed 15 deg. Hotter = less-dense air introduced to the intake. The engine operating temp. remained a constant, water temp. regulated. The engine didn't run hotter. The water-temp sender would have sent the same output to ECU. However, that doesn't rule out the sender as suspicious for overall idle problems.

The hot day effected the mixture. It would be heading toward lean like a vac leak which creates poor idle. The electronics should compensate richening it from O2 and other inputs like temp and altitude. Altitude changes mixture where higher becomes leaner.

Rougher idle points to mixture not ignition. RB's smoke monster could be a call away from a shop that can perform leak tests. Temp senders are cheap.

 

So there is a water-temp sender and a water-temp sensor? I see them both on a parts site.

I was doing some research and I read that the water-temp sensor (assuming thats what the coolant temp sensor is) sends info to the ECU, so then adjusting the EHA valve accordingly. They said its unlikley, but a possibility. If I have an error code for it, and there is a possibility, then it needs to be done. It looks very cheap too (new $25).

How can I read the codes myself? Do I need a special computer to read them? Where can I find the list of codes?

Thanks,

 

Does that year have a crankshaft and or camshaft position sensor. I have often found that rough idle and stalling out is a result of that sensor going bad. You press the gas and it will somewhat compensate but at idle you get rough idle, or even stalls. Just a thought.

 

I believe it has a Crank Pos Sensor...Can I test the resistance on it to see if its good or not?

 

You could put it to a meter and check it as you would any other electrical sensor. To be honest it is something that is routinely replaced anyhow and if it is not bad now chances are it will be later. On GM's (i know it is not a fair comparison) the CPS is the #1 reason for no starts and stalls. If it is not too much $ i would just swap it out. You will know immediately if it was the issue.

 

That CPS runs about $160 non-dealership and is a special order part (autozone part # SU4733) Hope this helps

 

Yeh the local place has one for $140.

I'll probably do it next pay period.

Its another $140 ya know?

 

Hope that fixes it. I am surprised the techs didn't suggest the CPS.

 

I am assuming they were all thinking it was something more common.
I really hope it fixes it too! I have been fighting it for almost 2 years now. Kinda sick of it ya know?

Oh and should it be normal that when I turn on the front defroster the economy gauge goes up?

 

Economy gauge is vacuum operated......only thing that will make it move is a change in the vacuum it's seeing.