I just can't seem to figure out what's wrong with the car in my sig. It bogs when you first get into it. Once it gets past the bog, it accelerates normally. At idle, it kind of acts like it's loading up on fuel. It actually started doing this almost a year ago, but 6 months ago, I bought another car. It's been parked ever since. Now I'm ready to see if I can finally get this thing running right.

I plugged in my scan tool. At idle, the O2's should bounce around, but have a 450 average. Mine do that, but every minute or so, they start dropping down until they get to around 50-60 (too rich?). After a few seconds down there, they come back up to normal. All of the other sensors appear normal.

I first thought it might be a missfire, so I replaced the opti and plug wires. Didn't help.

Then I thought vacuum leak, so I grabbed a can of starter fluid and started spraying everything. RPM didn't change.

Next I thought fuel pressure regulator, so I checked the fuel pressure. At idle it holds at 39-40#.

Now I'm running out of ideas. Anyone have a idea of where to look next?

 

Go back to the O2 readings and monitor them and the fuel trims after it goes into closed loop. You will expect to see the O2 readings switch from low (lean) to high (rich) numbers continuously. If they are staying at one reading, there is a problem. Pay attention to what the fuel trims are doing at the same time. If the numbers are sluggish, test the harness.

Also, remove the plugs to see what their condition tells you.

 

Wait, low numbers are lean?!? I've been looking at this wrong the whole time. OK, back to square one.

The numbers do jump around, but every minute or so, they steadily drop for about 10 seconds. They still jump, just not very high (100-250). While doing this, the engine stumbles noticably. After bottoming out (50-100) for a couple of seconds, they come back up (150-750).

I have the bog all the time(open and closed loop). I don't remember which it was in when I scanned it.

 

Thats sorta the same problem I have.. It bogs down at take off but after 40 it accelartes just fine.. Does it want to take off on you at a red light while braking? So far ive changed taken apart the iac and it looks clean and i changed the pcv hose .. Still have the problem

-Ben

 

When it comes back up from the stumble, I suppose it could feel like that, but it's just getting back to where it was.

I'm going to pull the plugs today. I really hope I don't have to pull the headers to do it.

 

Let me know if you find anything .. It can probably help me out ..

-Ben

 

accel opti? That would be questionable to me.

Could be dirty clogged/bad injectors.

Have you checked your vacuum? Harbor freight has a nice vacuum gauge for 10 bucks.

 

It did it with the old GM opti, so I don't think it's the Accel.

I had considered the injectors. How would I check them?

I don't have a vacuum guage. I did spray starter fluid all around the top of the engine while it was running. The rpm didn't change.

 

If the leak is between intake ports, the spray trick won't work, but air will be leaking from one cylinder to another.

Sounds like dirty injectors. I fought the same problem for a month. I adjusted my valves about 50 times, replaced plugs twice and replaced plug wires. It was bad injectors.

Use a stethoscope or take a long screwdriver, put it on the injector and put your ear to the handle and it should click. I did this trick on my last set of injectors and they all sounded good, but as it turns out, they were not.

They also measured between 16.1 and 16.3 ohms on all 8, and they're still bad. So I'm guessing they're just really dirty and need to be cleaned.

If I slowly accelerated I could take it up to 6500, but If I gave it more than 3/4 throttle, it wouldn't move.

I don't want you to fry your injectors, but this is how I used to clean injectors on my TSI (different design injector tho...).

Take a 9v battery, and run it to one of the terminals on the injector, ground the other. This will open the injector. Then I'd shoot some brake cleaner up the injector and it would spit a good amount of dirt out of them. Don't use 12v because I don't know if it could fry the injector. They're used to getting pulses. I wouldn't leave it on the 9v for long. Just enough time to spray them out.

This worked for me on my last car. I haven't tried it on my 30# svo's yet.

You should def. change the plugs tho to see if that helps, if they haven't been changed in a while. If they're not too old, pull a plug and see how it looks. If it looks good, I wouldn't waste time with that until you've ruled out any kind of fuel issue.

Sounds like you have a fuel issue, not an ignition issue.

 

It sounds like you need to let the car warm up for 5-7 minutes. Test the O2's and see if they go between 100-900 and never for more than a moment and you see high and low readings. If you get anything but this replace before you do anything else. The Ac Delco are $40 each and have a great track record and the aftermarket ones have all sorts of problems.

 

mrmint69, they do jump around like that, but every minute or so, the numbers steadily drop for about 10 seconds. They bottom out around 50-100 for a few seconds and then come back up to normal.

raroz28, good point on the intake ports, but I'm thinking it's injectors too. I actually had them serviced about 6 months ago, but it didn't fix the problem then. I was going to pull the plugs today, but got side tracked. I'll pull a couple tomorrow, but if I don't see anything unusual, I'll try your screwdriver trick.

FYI The car accellerates fine once it gets past the bog. It stumbles, then takes off normally. It doesn't matter how much pedal you give it either.

 

If the numbers are below 450 most of the time. There is problem. They should be switching from below 450 to above 450.

I wanted you to monitor the fuel trims. Mine had a burnt O2 harness before the O2 connector. On the passenger side where the harness goes down from the top of the fender to the starter. This harness has the right O2 wires in it and is wrapped with foil. Inside the wires had NO insulation from being cooked by the header.

The O2 reading was staying high (rich) and the fuel trims were pulled to as lean as it would go. Then the PCM pop out into open loop momentarily. At that point it would run good. Then it would go back to closed loop and continue to pull fuel until it started all over again.

I tested the harness by shorting the 2 signal lines to the ground line. This should produce a low (lean) number at the PCM. However in my case, the number never changed from showing it was rich. I new that the harness had a break in it and started looking at the foil area since it was obviously too close to the header. I stupidly thought the foil would protect it.

The other thing that was tip off was the fuel trims were going lean but the O2 readings stayed the same.

Just my 0.02.

 

I pulled plug 1 and 3. At this point, I'm just going to replace all of them before moving on.

 

It's interesting that you reported your O2s say it's lean but looking at #1plug tells the opposite.

Also looks like the gap was quite large compared to the other plug.

What's the fuel trims doing?

If 1 continues like that but the others stay clean, let us know.

 

The gaps are actually the same. It's just the angle of the pic.

I noticed that the plug looked rich also but I have to pull the headers to get them all out. I have to get my jack back from my brother-in-law to do that.

I may not have to do it though. I have a guy who want's to buy it as is. I've explained the problem to him and he wants it anyway. We have agreed on a price, but there's the issue of getting it to him (he's a few hundred miles away). He's suppose to let me know later today if he can find a way to tow it home.

I do appreciate the help, and if the sale falls through, I'll get you those fuel trim numbers.