Bizzare problem
 

This has been going on for a couple weeks now. Here are the symtoms: When the engine is cold (like sitting over night) then car will idle really low (300 rpm) and ussually die if I don't give it gas, sometimes it will just idle at 400 and then rev up to normal idle (900). When it is idling low the volt meter drops to about 6 - 7 volts.

When I am driving the car, it is down in power and runs rough. like a lawnmover. I borrowed a scanner from my uncle (he runs a Sunoco station) and hooked it up. A few problems came up after the testing cycle. First, EGR sensor contaminated, O2 sensor bank 1 short. I had cleaned out my EGR about 3 months ago when the gasket between the EGR plate failed. I cleared the codes and did it again. Only the o2 sensor came up. The fuel pressure was OK (about 38 psi at idle) . I checked the o2 sensors with this $5,000 graphing volt meter that I borrowed. the voltage was low idicating that the sensor thinks the engine is running lean. All the other sensors are saying the engine is running rich. It is def running rich becuase if I try to accelerate when the engine is cold, it makes small backfires, and at night you can see small flames coming out of the exhaust. Also, when the engine has been sitting overnight, if I try to accelerate, it makes these knocking/banging sounds, like someone hit the heasders with a mallet.

I changed both o2 sensors (I have that 3 day battle in a different post, funny) and the problem went away for a few days. but now it is back. If I disconnect the battery for a while then hokk it back up, the car runs like normal for about 10-15 minutes then suddenly goes back to the way it was.

I don't have access to that equipment until sat and I really need ideas. Anyone???

well the running for 10-15 min then running bad is the computer going from closed loop to open loop and getting the info from your o2 sensors and fouling things up. so maybe there is something making the o2s go bad and changeing them just masked that ? i have a hole where my passenger o2s use to be and the car runs good untill it warms up and then runs like crap i just turn it off and turn it back on have to get time to get a bung welded back in.( i hade to lower the boost because i blew off the peice i brazed over the hole)

have you checked tps voltage ? or changed your tfi moduale ?

Is there anyway to eliminate those bastards anyway? I hate them things.

You need to inspect the wiring harness to the O2 sensors. It sounds like there is either a short in the wires, or part of the insulation has worn, or burned, away. Check the wiring.

Take care,
-Chris

I can't believe I didn't think of that. When the full length headers were installed, the o2 wire harnesses were extended. The scanner said there was a short in the o2 sensor, I will have to check the wires then. The installer might have done a bad job. But that was done last year, and my problem has only been going on for a couple of weeks.

It could have taken this long to melt threw the insulation for the o2 sensor wires. Funny how these things delay themselves so you can't figure them out.

Ain't that the damn truth!!

Ford says that 02's need to be within 17" of the exhaust ports for perfect world, with my long tubes I had same problem, there is a calibration code that determines which 02 sensor you need, did you buy a universal type or motorcraft units? The code is on the drivers side door area.

I bought 2 new Bosch sensors. I hope that the faulty harness (maybe, havn't checked yet) didn't destroy my new sensor, there goes another $50......:(

Any master mechanics in the house?
 

O.K., I spent some quality time with my car over the 4-day weekend. Here is an update.

I was able to use my friends garage where he has a dyno and just about any scanner/tool you can think of.

the first thing I did was look at what was coming out of the exhaust. They hydrocarbons were off the chart, pegged at 2000 ppm. So that confrimed it was running rich.

I pulled a bunch of plugs and they didn't look too bad, a grey color, not too bad, but still rich.

I them put the car on the lift to get a better look at how the o2 sensor harness was routed. Not bad, but I pulled it out of the car and took a careful look at it. It seemed fine. I was expecting it to be burnt or broken.

I then checked evey sensor, BMAP, TPS, MAF, etc. Everything checked out O.K. , Except last time my FP was at 36, now it was at 30:( I tapped the fuel press reg, and the pressure jumped around, so I ordered a new reg. But that coulndn't be all of the problem, the car was running slightly rich.

I then took a propane canister and injected some of it into the intake while tapped into the O2 sensors. As soon as I hit the valve, the graph jumped up and responded imedaitly to the inrichment. So the o2 sensors and harness were working fine.

I also knew that a vacum leak would cuase these problems but I couldn't find one. I got the idea to go around the engine with the propane tank and check again. Well guess what!, there was a small leak in the diaphram of the EGR valve. So I made a Plate out of aluminum and blocked it off. The car ran a lot better!, but not totally back to normal. After I get the regulator installed I hope it will be.

What does the deletion of the EGR valve do to drivability/performance?
Anyone got any ideas? Anyone ever have similar problems? Any input would be VERY helpful!

Any other ideas?