Just wondering how many others have the low speed stumble and just live with it. A 160 deg thermostat and manual fan switch keeps mine at a minimum. Just for grins I will include my list of attempted remedies. Plugs, wires, opti, coil, TPS, EGR, MAP, temp sensor, injectors, O2 sensors, and fuel filter changed. Cleaned throttle body, relocated coil and ignition module. Installed off road pipe. Seafoamed it. Blocked the egr. Checked fuel pressure. Cleaned the idle air valve. Throttle body bypass. Bypassed the knock sensor. Checked voltages and grounds to all sensors. Some of these things stopped it for a short while, then it would be back. Since it's a 93 theres no MAF to change. No codes. No arcing wires. No vacuum leaks. No exhaust leaks. Reset the computer, many times.
The manual fan switch and 160 stat git rid of it pretty well, you wouldnt notice any stumble unless you look for it. When the temp hits 190 it turns into a real slug until 2K rpm, then runs great.
I have considered taking it to the dealer for scanning but have heard enough horror stories about them so that I cant bring myself to do it.



93Z M6 RED
B&M Shifter, 58K
egr, tbb, offroad pipe

 

Going out on a limb here but follow along. Remember that in open loop the fuel ratio is richened up. Then in closed loop it takes measurements and directs fuel ratio accordingly. I'm thinking lean condition. Open loop richens it so its fine but closed loop is too lean. If you haven't done so get your injectors professionally cleaned. I do it with a 3m kit hooked directly to fuel rail and regulator disconnected and vac line blocked. Remove the fuel pump relay and car runs off the can of cleaner for 10 minutes and shuts down.

I recommend a car that hasn't had this done in long time use 2 cans. When the can is empty, the engine shuts down. Reconnect every thing and try it.

One question, when you checked the fuel pressure (we assume at idle) did you check it both with and without the vacuum line connected to the regulator. You need to see if the pressure jumps up when the regulator is disconnected. Don't forget to plug the vac line when you disconnect it.

If that doesn't do anything, check exhaust back pressure. Easy to do if you can get downstream O2 out.

If that shows less than 2.5 psi than check fuel pressure while driving. Tricky but can be done. Don't run long with the gage on, it's dangerous.

I have a feeling cleaning the injectors is gona cure your problem.

Hope that helps.

 

badass,

just wondering, where do you get the 3m injector cleaner kit? I've been looking for something like this for some time now but haven't found anything in the local car supply stores..

 

Sorry it took so long to get back to you. The kit normally has a lot of things you don't need. And it costs about $300.00 cause it was designed for shop use. I went to a very knowledgable NAPA store and they ordered me the hose and adapter for $100.00

Yeah I know that's a lot but I use the s@#$ out of it for me and friends. According to the papers I got with it the 3M PN is 08914. I think the adapter for connecting the can to it comes with that. Don't loose the adapter for the can. You can't buy it seperate. I had to buy another hose cause I left it attached to a can when I tossed it.

There are different cans of cleaner some use a regulator but I use the can of 08912. It does not require the regulator. Cost at NAPA is about $16.00 per can.

AS far as I'm concerned, this is the only way to clean the injectors with out removing them.

Hope that helps

 

Hey seabat, I just noticed (didn't the first time) does your first thread say you put in NEW injectors?

Scanning is ok at a dealer, just tell then you do not authorize any work be done. Try a local shop. If they have a good scanner they can see the data real time.

Have you done the basic checks such as compression and leak down? Good things to eliminate as you search.

I'm gona say you have a restricted exhaust. considering you replaced just about everything else. Easy to check from the O2 bung if so. Maybe some others can chime in on this one. Sorry I didn't notice before you changed the injectors. Got my piston up my tail pipe sometimes.

 

I think you are running rich as well. I was getting like 111 BLM's on both banks and I just needed some tuning.

 

I know how you feel. I've been living w/ a stumble for the past year now. I've done everything you have done plus some. I'm working on my car right now and I have the headers off it. I found a leak on one of the primarys and one on a collector right before the o2, so hopefully thats my problem. But I'm thinking thats not my problem because I've had exhaust leaks alot worse before and I never had a stumble.

While I have the headers off I'm gonna do a compression check, but I think it will turn out ok because when I checked my vaccum it was dead on.