QuestionHoward,
Ok, I just ran those two tests. As for fuel pressure, by your info it would seem I have a bad regulator as I ran the vacuum test first, and had a residual 20 PSI in the fuel line, but when I opened the MAF flap by hand, it went to 38 PSI, then on up towards 70 PSI or so when I pinched the return line. I'm ok with that. As for the exhaust, it went right up to 6 and 7 PSI with revs to 3500 and 4000 RPM, 2 PSI at 1000 - 2000 RPM. I'm sure you understand how difficult it is to be exact with these measurements, but by that measure, it does seem the exhaust is clogged. Now, I can say I already suspected this much early on, but detected what I felt to be equal pressure output at both tail pipes. Is it your experience that the Cat converter is the common source of the blockage? I am familiar with how their internals can break loose as I had this problem with a Land Rover.
Thanks,
Michael
AnswerYes, the regulator is bad. Residual pressure is of no use. Only pump pressure with normal vacuum on the regulator (32 PSI) and low or no vacuum on the regulator (42 PSI) The high pressure with the return line pinched indicates the pump is probably ok.
The exhaust back pressure of 6-7 PSI is sure indication of a stopped up exhaust. That is the cause of vacuum going to zero. The fact that you feel the same exhaust out of each pipe makes it most likely one or both of the CATs as they are in line. Most likely it is the first CAT as it catches the worst of raw fuel in the exhaust and thus melts down. With the first CAT removed you can look in it to see how bad it is and put a new first CAT in and try the exhaust back pressure test again to gauge the second CAT.
The most common cause is a dead cylinder either due to a mechanical or electrical problem. Any thing that can put raw fuel in the exhaust.
Yours is only partially stopped up. I have had them so stopped up that they would not start. Zero vacuum on cranking.
I believe you found your problem, let me know.
Howard
