Question: 1998 Mazda 626LX
Mr. Ciulla, I have a question concerning a 1998 Mazda 626 LX I am working on for a friend. Originally it was throwing code P0171, System too lean. I found a small vacuum leak around the intake manifold, retorqued the manifold bolts and reset the computer. CEL came back on about 80 miles later with 2 new codes. P0117, coolant temperature circuit low input & P0421, Catalyst warm-up below threshold.
My question though, while troubleshooting this car, it got to a point that it did not even want to start. I pulled the plugs and noticed fuel loaded up in the cylinders. I pulled the plugs one at a time to blow out the fuel in the cylinders and then checked the spark on each plug, checked resistance on the plug wires (good).
Checked fuel pressure before and after the fuel filter, now my question. I was not getting any fuel pressure at either checkpoint by just turning the key to ON, when I bumped it over to start, I was getting 75-80 psi. That is a lot higher than it should be (granted my fuel pressure gauge is NOT calibrated) but should I suspect the fuel pressure regulator for not getting rid of the excess pressure and is their a way to test the regulator. I did pull the vacuum line off of the regulator to see if possibly there was a hole in the diaphragm, nothing. I think it could also be an injector(s) putting out to much fuel.
Thank you for your time and sorry for such a long email.
Thank you,
Rick Shepherd
Answer: 75-80 psi of fuel pressure is within the spec of 69 - 92 psi so the fuel pressure is correct. What's probably happening is the bad Coolant Temperature Sensor (CTS) is telling the PCM the engine is much colder than it is and the PCM is increasing the fuel to comensate. The excess ruel would, in turn, cause the P0421 code. I would suggest checking the CTS circuit for an open and if that checks out to replace the CTS.
Question: 1994 Volvo 850 GLT turbo
Just wanted to see if you had an idea. I have a 1994 Volvo 850 GLT turbo. The other day the battery cable that powers the electrics broke. I fixed it, then noticed that the MPG computer doesn't read correctly.
It started at 100 MPG and then it goes down to 6 MPG, then goes back up to 11-14. When I accelerate harder the MPG goes back up, when I coast the MPG goes down. Opposite of what it used to do.
Any ideas before I bring it in?
Answer:This is a new one on me. The only thing I can suggest is to disconnect the NEGATIVE battery cable for a few minutes to see if it will reset. If not you may have hit it with a voltage spike and damaged the unit.
