88 Carrera not running right after premuffler and O2 sensor install
 

The car was running fine before I made any changes, although very sluggish due to a clogged cat. I installed a euro premuffler and replaced the O2 sensor with a universal Bosch sensor.

When I first tried starting the car, it would barley run and I had to crank for several seconds to even get it to catch. I double checked the O2 sensor connection and tried again. It would barley idle, then die after about 10 seconds. Then I disconnected the O2 sensor and tried again. It idled, but I couldn't give it gas or it would sputter and die. I let it idle for a little bit, and I could rev it up but I had to feather the throttle. I then drove it around the block, and if I gave it any gas or load it would sputter and almost die. If I feather the throttle I can get it going, but I have to slip the clutch a lot to not put too much load on the engine or it will sputter and almost die. If I do give it gas under load it backfires. Once above about 3,500 RPM it seems to run fine and I can floor it to redline with no ill results.

Edit: My problem ended up being incorrect spark plugs. See below for detail.

Let Me Know What You Find
 

Similar problems with my car:

-Starts OK, and idles fine once warmed up.
-Intermittent but very frequent sputter when rev'ing the motor (in neutral).
-Intermittently sputters and acts like it's going to stall when accelerating.
-Allows intermittent acceleration up to red line, but then the RPMs fall and the engine nearly dies.
-I'm fairly confident I'm getting adequate fuel flow: 1 mile trip around the block (RPMs dropping and then accelerating again) turned the catalytic cherry red (I assume from unburned fuel making its way into the cat).

http://forums.pelicanparts.com/porsche-911-technical-forum/491197-3-2-dme-issue.html?posted=1#post4833126

If I resolve it, I will give you a heads up. Appreciate if you could do the same.

Best of luck,

Gordo

The O2 sensor is not the good one on my own.

No one has any idea what this could be? I let the car sit for 4 days and it's much less pronounced now. It is drivable, but still stumbles/hesitates/misfires if you blip the throttle at idle. It also seems to be running very hot still. I thought replacing the clogged cat would solve that, but it didn't seem to make a difference.

New plugs, new wires, new O2 sensor, new cylinder head temp sensor, new battery, new distributor cap, new rotor, new air filter, new premuffler, and the list goes on.

I'm ready to dump this "reliable" Motronic system and put CIS on this thing. My SC has been less troublesome in the last 7 years than this Carrera has ever been. It's been a sluggish dog ever since he got it and we've thrown parts at it left and right hoping to find the problem but nothing seems to work. Now this pops up from changing the cat and O2 sensor. I'm stumped. I guess I'll replace the AFM next and see what happens. I'm not optimistic though.

You can always open up the motronic box and look for cracked solder joints. If you find any, just re-melt. Mine had 2, though it was still running fine when I checked.

Well everytime something bad happens from installing something you need to trace your steps. Put the old O2 sensor on. Could you have bumped anything, or hit any connection in the engine compartment?

Are you sure when you installed that plain Bosch o2 Sensor you didn't mess up anything else like the wiring etc.

Slow down and retrace your steps, 9 out of 10 times it was something that you might have done.

Hey just a though.

JW

And if that doesn't work you might want to check this out
http://www.914world.com/bbs2/index.php?showtopic=67906&st=20&p=861736&#entry861 736

Also worth checking out the ICV

Which Bosch 02 sensor did you install? There are a few different part numbers. I used part number 13953 and it worked beautifully...just a thought.

Unplug the O2 and see how it runs.

I actually leave mine unhooked and my car is mostly for track fun.

This might give you an idea if somthing is wrong with that part of your change over.

O2 measurements OK?

+1.

If all you did was replace the cat and o2 sensor, one of those is the cause of your problem, and I doubt the cat pipe is it. Try unplugging th O2 sensor and see how it works.

The only other thought I have is the muffler. You said your cat was bad, any chance pieces of it came apart and are lodged in the muffler?

Also, what made you think your previous running problems were the cat? Perhaps you have another problem somewhere? Poor idle, lack of response below 3500 sounds like an air leak to me.

yes - do this - i know our cars are 8 years apart and on different fuel systems, but when my car was having similar problems yours is(mine would run rough ALL the time, missing at idle, etc), i went through a million things before i took it to a shop... he set the mixture at 3.5% CO and resoldered a couple of solder joints and it runs amazing now. if i remember right someone told me 90% of all fuel problems are electrical.:cool:

Now that's something that I hadn't thought of. I will check it out. I have a Wong chip on the way so I'll be opening it up anyway, but I'd really like to get this figured out before I put the chip in.

One thing that I really like about newer OBDII cars is that there isn't much guess work with sensors. With these older electronic fuel injection it's trial and error until you find out what the problem is. And it gets expensive replacing parts that might not be bad.

I installed a universal that I got from Autozone. It is an 3 wire that fits an 86 Ford Taurus, and I've heard success from others that it works. It's been unplugged since it started running rough though, and it hasn't helped or made it any worse weather it's unplugged or not.

This is the process I am following now. Thanks for the advice.

It has been unhooked and has no effect (or is that Affect???)

The cat actually looked fine from the muffler end, so I don't think anything made it into the muffler. When I shined light through the cat from the other end though, I could see melted parts at the beginning. The muffler is on my list of things to check though, I just don't know how to tell if it is clogged. I do have an old SC factory muffler that I might try out on it and see what happens.

I'm not entirely sure it was the cat that was the problem, but I think it was part of it. I've been replacing parts (as I listed above) to try to trace down a poor performance problem with this car for about 2 years. The premuffler helped out a lot, so I'm pretty sure the cat was clogged. It now revs up MUCH quicker than it did before.

Thanks, this is on my list of things to try next.

Thanks for all the help!

Just shooting in the dark.

A surprising number of running issues comes from a clogged fuel or air filter.

Check the lead from the coil to the distributor and look for burning at each end. Inspect the coil. Look in the distributor cap for issue/burning.

Check for manifold/air leaks (carb cleaner sprayed in suspect areas).

Check fuel pump by checking fuel pressure.

Check the AFM for liner voltage output when moving the barn door manually.

Look at a couple of spark plugs.

Check compression...

When was the last time the mixture was set via CO%?

The car in question is an 88 Carrera. I didn't think that was necessary or possible on a Carrera.

I have a load of things to check from the suggestions here, so hopefully I'll have good results to report back in the next few weeks.

Problem solved. It turned out to be the spark plugs. I replaced them along with the wires a few years ago, but decided I'd check them to see how they looked. They all looked ok and had a slightly ashy brown color. I noticed that they were platinum plugs and they were all gapped wrong. I remember reading somewhere that these cars don't like platinum plugs, so I replaced them with Bosch copper plugs. I think the clogged cat was somehow masking the bad plugs. The car runs like a dream now. My euro SC is still much quicker though ;).

Moral of the story, don't forget to check the simplest things first.

Things I checked during my troubleshooting process:

-new air filter
-took apart AFM and adjusted it to run on a new track
-checked for vacuum leaks with propane and carb cleaner.
-checked plug wires by spraying a mist of water over the engine while running
-left O2 sensor unplugged to eliminate it from the problem list.
-opened up Motronic box and checked all solders for cracks.

Well I spoke too soon. The problem is all of the sudden back, and worse. The POS just left me stranded at Lowes. I managed to get it home, barley, after letting it sit for about 30 minutes.

I has been running great. We took it on a few road trips and it was running stronger than ever. I've driven it about 2,000 miles with zero problems. The it sat for a few days because it has been raining, and when I tried to start it this morning, it barley started. (that should have been a sign to not drive it). On the way to Lowes, about 2 miles away, it starts sputtering on acceleration. Then it died at a light. Managed to barley get it started and limped it into the parking lot. Wouldn't restart. After about 30 mins. I came back and was able to barley get it started and limp it home.

I could smell gas when I was cranking it. The DME relay clicked twice, once when ignition is turned on and once when cranking. It seems like it's not getting spark, but I have no idea why. It also seemed to be running rich. When I pulled it into the garage the fumes made my eyes burn they were so strong.

Any ideas before I drive, no push it, off a cliff?

Don't push it off a cliff just yet! Although it's a terribly frustrating problem for you, it's not one that appears catastrophic or chronic.
It does sound kinda like a spark problem, you changed spark plugs but next I suppose I'd check to see if there was spark getting to the plugs.
It's easy to conclude that the problem is related to the premuffler/O2 install, but having just done that SAME procedure (including the aftermarket universal O2) on my 88', I can't see any obvious connection between the premuff/O2 and the serious running issue you're having.
Doesn't sound like a DME relay problem.
Could be a CO% issue, but why's it intermittent? (After I replaced my O2 sensor, my AFR needed to be readjusted to lean it out, it had been running too rich.)
After verifying spark, fuel, AFR, ICV, Idle position switch, etc, I'd probably try to borrow another Pelican's working DME and swap it out to see if there's any immediate improvement.

Also, barely, not barley, your post was making me thirsty :)

I'd like to try to help, especially since I just made the same improvements to my 88'.

verify spark. Pull the coil wire from the distributor cap and point it to a grounded source such as the intake manifold, about 1 inch away. Cranking the car you should see a spark arc out. If not, it could be the coil, or DME. If you have good spark, check that your distributor cap and rotor are clean and properly seated.