Well folks,

It has been a while since I have been on this site.

My latest project of restoring a fishing boat for my Grandson has been eating up all of my time.


Anyways…….

Recently, I started an issue with my 96 xjs.

It seems upon startup it runs rough and spits out soot from the tailpipe. After it starts warming up it get better and when it get to normal running temp……NO ISSUE!!!!!!

SOMEWHAT PUZZLING? Since I installed a new temp sensor this morning….thought that would solve my issue.

THEN

1. pulled off idle air and cleaned
2. pulled off the EGR.. and cleaned soot….the plunger seems to move smoothly. I don’t know how to check diaphragm?
3. Pulled off upstream O2 sensors and cleaned…seems to runs a bit smoother upon startup and smooths out quicker….possibly because it wasn’t quit completely cooled down.

This situation started a couple of weeks ago when we had the really cold heater in florida….temp in the 30’s .

It would startup but runs rough for a while…….WET SOOT ALL OVER MY DRIVEWAY!

Also did notice some soot around the EGR VALVE ….FEW DROP HERE AND THERE…LOOKS LIKE IT NLEW OUT OF THE VALVE.


Please render your wisdom ….I need your help!!!


Softball60/Paul

 

Paul,

it seems it's massively overfuelling when cold. forgive the question, but you did change the temperature sensor (2-wire plug) rather than the temperature transmitter (single wire plug)?

As a rough diagnostic, try disconnecting the temp sensor plug before the next cold start and bridge the 2 terminals in the plug, then start the car and see if it is better.

Good luck

Paul

 

How old are your oxygen sensors? If you don't know the answer, I'd recommend replacing them. They could be dying, just not enough to throw the CEL...yet.

Could a filthy EGR sensor cause this too? I think so.

A failed coolant temp sensor could also be causing this problem. A very cheap and easy part to replace.

When was the last time the throttle body was cleaned? They get filthy over time and can use a cleaning, but that can throw off your idle, so let's not start here.

After that, we get into checking spark plugs and replacing coils....

 

I replaced the two (2) wire sensor….I don’t think this is the issue.

The EGR HARDLY HAS HARDLY ANY MILES ON IT.

It was okay till the cold weather hit!!!

At some point soon I will purchase Two(2) upstream O2 sensors. I believe these are the ones sending signal back to the computer.

Like I said, after it comes up in temp, it smoothies out.

Softball60/Paul

 

Paul,

Apart from the lambda sensors heating up, I think that the only thing indicating a signal to the ecu to enrich the fuelling when cold is the coolant temp sensor. So try disconnecting it and bridging the plug as suggested and see if the ecu fuels differently.

Paul

 

No. Regarding the oxygen sensors, on these cars, its the downstream sensors that do the heavy lifting. I'd have replaced all four, but maybe it is something else.

How old are the spark plugs? I'd consider running the car from cold for a few minutes, and before it gets better, shut it down and take a look at each of them. See if any are wet, or charred. That might help you find a leaking injector perhaps? Or maybe a coil that isn't behaving when cold. Once warmed up the cracks on the case expand enough to get them to work well.

You might have a leaking seal, allowing oil to enter the cylinder. Again, once warmed up, everything expands enough to keep more oil from entering cyinder?

 

While I may be on the wrong track here, I'm thinking it could be Vacuum, as if that pipe is being blocked the ECU will do its thing and over fuel the Engine

So wondering if the Vacuum source could be relocated somewhere else, ie to the rear of the inlet manifold

Just throwing it out there to hear what you other guys think

 

What vacuum are you talking about?

There's a hose connecting the camcover to the elbow between the MAF and throttle body. I always assumed that this hose gets is positively pressurized from the camcover.

The only other connection would be the pipe between the EGR and the exhaust manifold.

I do agree that a vacuum leak would cause this condition as well, I just assumed the PO checked for one.

 

Hi Vee

The First one

 

Quite frankly, you can block it off at the elbow, but the hose side will spray some oil deposits out while driving. I ran mine through an oil catch can, but I learned that I can disconnect the hose connecting the oil catch can back to the elbow. The can should catch the oil vapor, so the air coming out of the disconnected side of the catch can should just be hot air.

That would eliminate the possibility of the engine creating any issues, but I don't think that is the case here. Temporarily unplugging the hose from the elbow, and capping the elbow port with a short piece of hose with a bolt in it, clamped in should reveal any changes.

 

Not sure I understand what you are talking about with vacuum issues.. I will pull hose and look at.


I did short across the temp sensor………IT WOULD NOT START!!

Not sure if I mentioned but the EGR SPIT OUT SOME SOOT. NOT A LOT . I CLEANED AND REPLACED.

Have not done anything else at this point.

thanks

Softball60/Paul

 

Please check all of the unions and connections of the hoses between the MAF and the intake manifold. You may have a hole, or a gap somewhere there. I wouldn't worry too much about that hose from the camcover to the elbow...but while you're there. Often times people misalign some of these pipes when reconnecting them, or maybe forgetting to tighten something up. You don't need to strongarm any of these hose connections, snug works just fine here.

I am not shocked the car would not start with the coolant temp sensor jumped, since the engine is cold, and jumping the sensor tells it that its hot, but I am rather surprised. I didn't think it would do that. An OBD2 sensor would tell you if the coolant sensor was giving the ECU bad information. You should really get one that can display ECU info. It's not expensive, and it's invaluable for reading codes and troubleshooting.

(Can I assume that you jumped the harness pins and not the sensor itself?)

 

If it is rough immediately upon starting I don't think your O2 sensors are involved, they take a short time to warm up and start operating. I would be concerned with fuel age and quality, fuel injector operation and spark plugs and coils. If it is OK when warm the coils probably are OK but worn or dirty spark plugs or injectors with poor spray patterns are a likely cause of rough running cold.

 

Well it has been a bit. Thought things were getting better when fired up in the driveway….so took it for a ride…….MISTAKE!!!!!!!

The more I drove the worse it got. No acceleration, then clear up. Took it on the expressway and it starting slowing down. Got off the highway trying to get home. Finally stopped running and died at a roundabout….WHAT A MESS I CREATED WHILE TRYING TO PUSH IT OFF THE CIRCLE.

IT would fire right back up but died in a second.

Some kind people from Delaware helped me push it off.

waited for the tow truck to pick me up and take me home.

HERE IS MY TAKE.

Got it home and for giggles tried to fire it up. IT STARTED RIGHT UP AND SOUNDED GREAT….Then it died.

I THINK IT’S THE CATALYTIC CONVERTER. Builds up back pressure. Will start and run rich, blow black soot out tail pipe.

Everything I have research indicates so.

What do you think?

Softball60/Paul

 

Paul,

what error codes do you have?

Paul

 

PAUL,


Sorry for the delay in responding…..NO INTERNET FOR SEVERAL DAYS!!!!!!

NO ERROR CODES.

After it died on me and I sat for a while it fired right back up……Did not take a chance and waited for the tow truck.

After I got home it starts right up each and every time I try.

Will not take it for a ride and go through that mess again.

WHAT DO YOU THINK ABOUT THE CATALYTIC CONVERTER BEING THE ISSUE ????

Softball60/Paul

 

I don't know how to diagnose a cat converter problem without a code being thrown, which these cars are notoriously stingy with. The only advice I have read here in the past is if you can bang on them with a rubber mallet or something and hear something crunchy, it may indeed be the cat.

Have you checked your ECU for corrosion? A common problem is water getting into the harness connector. It would be a free and easy check. Make sure you have some kind of contact cleaner.

We've crossed off:
1. upstream oxygen sensors, you replaced them with new? (But not the downstream ones, which only provide a check signal, so you're probably ok)
2. EGR...not replaced, but cleaned - although you said it spit a small amount of soot out
3. Coolant Temp Sensor - replaced
4. MAF cleaned
5. IACV cleaned.

Because of the soot at the EGR, backpressure is certainly possible.
a. Have you taken the exhaust manifold shield off to check on the condition of the exhaust manifold? The EGR connects to the rearward manifold, by the way, perhaps you can check that connection for soot?
b. MAF might be bad? That could cause a problem, even when the engine is cold.
c. Did you check for vacuum leaks? Wrap the downstream end of the MAF in plastic wrap, pull off the hose at the camcover and blow smoke through that thing. (With the engine off!) Maybe at first, you can blow without smoke, just to see if it holds pressure?
d. Could also be a failing TPS. They do cause mysterious issues. No way to clean, or refurbish them. They aren't cheap either.
e. Catalytic Converter failure. Again, tapping with a mallet could help diagnose, but no easy way to be certain. Disconnecting the exhaust from the manifold to take a look is not a simple job. You would need replacement olives and single use copper nuts.
f. Have you ever checked the spark plugs? You could have a leaking injector, or a blown spark plug well seal. If you start the car cold, let it chug for a minute, or better yet, not start, and you can check spark plug wells for flooded oil? If all dry, you can then pull spark plugs to see if any of them are wet? A leaking injector would cause this. A flooded spark plug well could also cause this.

 

Vee,

Thanks for all the detail.

1. All four (4) oxy sensors were cleaned up a while back. Not many miles on cleaned units

2. EGR was new probably less than several hundred miles.

3. Coolant temp sensor new. Jumped the connector not the sensor itself for the no start

4. Clean theMAF every 6 months

5. IAC was also new but also cleaned

That pretty sums it up!!!!!

I have been busy with my boat project and it will be a while before I replace??? The catalytic convertor.

My question now is can it be eliminated….I have heard of a few that have removed it with success. What has to be done if I remove?

thanks

Softball60/Paul

 

1. Clean oxygen sensors are very different than new. They are parts that wear, therefore have a limited lifespan. They should be replaced if you don't know how old they are, but I don't think that's the cause of your issue since the sensors are not read at a cold start. It would be the reverse, it would start fine and then once the engine is warm, you would see issues.

3. No cold start when the CTS connector is jumped? Hmm. I have to ponder that one. That is a sensor that is read on a cold start. But you replaced it...

4. Clean MAF can still be a malfunctioning MAF, and it is read at cold start. This is not crossed off the list then.

 

Hello from sunny Venice, Florida. I live on the island of Venice and I own a scantool. Text me tomorrow at 941-416-4030 to schedule a time tomorrow for a look over.


Larry Louton