Engine knock


Question: 1987 Ford F-250 mileage: 150,000. Thanks for all of the great info on your page. A wealth of info to say the least. I have a question for you of which I am stumped. Living in Arizona I need to pass emissions and thus the need to correct something with the carburetor or emissions and I am hoping you can help. I just bought a 1987 Ford F250 460/7.5ltr with 150,000 miles on it. Replaced plugs, wires, rotor, cap, and made sure all hoses are connected. The carburetor is a Holley manufactured for Motorcraft LIST 50262-2 (E5HE-9510-MC). The idle was kind of high the first time I went in (~1500 rpm in park). The first emission test: HC (Hydrocarbons PPM) Loaded 185 (300 pass) Idle 275 (300 Pass) CO (Carbon Monoxide %) Loaded 2.53 (3.00 pass) Idle 5.2 (4.00 FAIL) I felt the idle was high and turned it down to ~900 rpm, replaced the PCV, Next test: HC Loaded --> 181 (OK) Idle 558 <--FAIL CO Loaded --> 2.08 (OK) Idle 8.37 <---FAIL BIG TIME! I have been looking all over the place to figure out how to set the idle mixture or where the screw is with no luck. Is that factory set? One last note. The previous owner put some type of hand valve between the PCV and the port on the carburetor. I did not find this till I was turning down the idle. It looked like it was perpendicular to the line (off) during the first test thus I opened it for the second test. I am unsure the reason behind putting a hand valve there? What do you think? Idle mixture adjustment? Timing? Any help would be great. Thanks again for your helpful site. Matt (Phoenix, AZ)

Answer: Check to make sure the carburetor does not have a slight internal leak causing raw gas to be drawn into the intake manifold. If okay, try replacing the catalytic converter. We have found that new converters clean up the emissions. Most Holley carburetors have an idle mixture screw on either side of the carburetor body.

I have this same engine in a 1982 bronco with ca. Registry, there is no cat and the idle screws arn't normal for holley's i'm also smog approved "no cats no computer 4 barrell holley" milage unknown recently had head gasket blow between 1 and 2 cylinder after repair, which included edelbrock performer egr smog legal manifold, all tune up items, partial carb rebuild, and new gauges , I temporarely eliminated some of the smog equipment (some vacum lines and float bowl vent to charcoal canisters ) but retained most of it. I was having problems tuning the engine when I discovered that if I disconnected the vac to the egr even with leak major improvement so I pluged the vac line and it tuned right in ((sorry so long )) went on a drive 250 to 300 miles and accuired a knock sounds too light for bottem end but preliminary inspection dosent show anything up top and the engine "runs" good but knock getting bad and had to tow last 50 miles. As it started temp app. 194 but oil pressure went to about 20 psi at freeway speed but is normal now 60/40
any ideas?
also vac pressure is said to be normal between 15 and 20 and if lew means "problems" can't find anything that refeers to high pressure either way (app. 22 or 23) steady and consistant
does this mean anything?

thanks for any help

Do you
have the same problem?
Thursday, January 4th, 2007 AT 2:24 AM

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