All,
About two years ago I posted a big write-up about how replacing my ACT and ECT sensors fixed my hot weather related pinging in the 3K to 5K RPM range under 3/4 to full throttle.
Well, two years later, my pinging was back! So, what, I say to myself, these sensors only last two years and then they’re bad again? But this time the pinging was there all the time, not just when it was hot outside, so it couldn’t be these sensors.
At this point almost all of the sensors on my car have been replaced (including new O2 sensors and, yes, cleaned MAF wires) so I was forced to look elsewhere for a cause.
Well, I FOUND IT! It was a vacuum leak at the intake manifold end of the vacuum hose that connects the intake manifold to the fuel pressure regulator!
This makes sense, since a leak there actually causes two problems. First, the fuel pressure doesn’t change correctly in proportion to engine load anymore since the FPR vacuum diaphragm isn’t getting the full manifold vacuum signal. Second, an air leak there allows un-metered air into the intake which the MAF never sees and thus incorrectly calculates load as a result. And our fuel/spark tables are what? Load based!
This hose is only about a 5 or 6 inch piece of 5/32 inch ID fuel hose. Mine must have been the original piece because it was completely hard as a brick and brittle. Since it was kind of hard to pull off over the flare on the fitting on the manifold side it really didn’t look like it could be leaking there, but it definitely was. It was hard to pull off because the hose was not flexible enough to get past the flare in the fitting.
The one-foot piece of fuel line cost me 79 cents. The hardest part was actually finding a 5/32 inch ID fuel line. It seems not to be a common size. I could find 3/16 inch ID fuel line at most car parts places. Though it’s not the best fit, it will work until you can find some 5/32 inch, which is a good tight fit. (Don’t try to use any thin-walled tubing for this, the vacuum will flatten it out and close off the hose. It’s got to be thick-walled fuel line or thick-walled emission control line.)
For the past week I’ve gotten all over it with full throttle runs (even with the AC on in upper 80 degree weather). The ping is gone!!! Can I get an “Amen”!
I hope this helps someone else with their pinging problem.
UNSOLICITED RANT ABOUT 94/95 PCMs: After working on this car for a number of years and reading many posts in this and other forums about how common this pinging issue is with our cars, I have come to believe that the cause is the combination of the “on-the-edge-of-drivability” load-based fuel/spark tables in the stock 94/95 PCM and the poor burn properties of the stock cylinder heads. If any single system or item under the PCM’s purview is just a little bit off, pinging will result. Because that combination puts us on the ragged edge from the get-go, nothing in the system can be allowed to age or deteriorate without causing pinging. Not sensors, not hoses, not EGR, not MAF, not squat!
OK, I’m better now!
About two years ago I posted a big write-up about how replacing my ACT and ECT sensors fixed my hot weather related pinging in the 3K to 5K RPM range under 3/4 to full throttle.
Well, two years later, my pinging was back! So, what, I say to myself, these sensors only last two years and then they’re bad again? But this time the pinging was there all the time, not just when it was hot outside, so it couldn’t be these sensors.
At this point almost all of the sensors on my car have been replaced (including new O2 sensors and, yes, cleaned MAF wires) so I was forced to look elsewhere for a cause.
Well, I FOUND IT! It was a vacuum leak at the intake manifold end of the vacuum hose that connects the intake manifold to the fuel pressure regulator!
This makes sense, since a leak there actually causes two problems. First, the fuel pressure doesn’t change correctly in proportion to engine load anymore since the FPR vacuum diaphragm isn’t getting the full manifold vacuum signal. Second, an air leak there allows un-metered air into the intake which the MAF never sees and thus incorrectly calculates load as a result. And our fuel/spark tables are what? Load based!
This hose is only about a 5 or 6 inch piece of 5/32 inch ID fuel hose. Mine must have been the original piece because it was completely hard as a brick and brittle. Since it was kind of hard to pull off over the flare on the fitting on the manifold side it really didn’t look like it could be leaking there, but it definitely was. It was hard to pull off because the hose was not flexible enough to get past the flare in the fitting.
The one-foot piece of fuel line cost me 79 cents. The hardest part was actually finding a 5/32 inch ID fuel line. It seems not to be a common size. I could find 3/16 inch ID fuel line at most car parts places. Though it’s not the best fit, it will work until you can find some 5/32 inch, which is a good tight fit. (Don’t try to use any thin-walled tubing for this, the vacuum will flatten it out and close off the hose. It’s got to be thick-walled fuel line or thick-walled emission control line.)
For the past week I’ve gotten all over it with full throttle runs (even with the AC on in upper 80 degree weather). The ping is gone!!! Can I get an “Amen”!
I hope this helps someone else with their pinging problem.
UNSOLICITED RANT ABOUT 94/95 PCMs: After working on this car for a number of years and reading many posts in this and other forums about how common this pinging issue is with our cars, I have come to believe that the cause is the combination of the “on-the-edge-of-drivability” load-based fuel/spark tables in the stock 94/95 PCM and the poor burn properties of the stock cylinder heads. If any single system or item under the PCM’s purview is just a little bit off, pinging will result. Because that combination puts us on the ragged edge from the get-go, nothing in the system can be allowed to age or deteriorate without causing pinging. Not sensors, not hoses, not EGR, not MAF, not squat!
OK, I’m better now!