engine missing at cruise
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Joined: May 2009
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engine missing at cruise
I have a 1989 F-150 with 5.0 liter and E4OD transmission. The truck has only 137,000 miles on it and I bought it new in ’89. I have a problem with a miss in the engine at cruise. I don’t notice it while accelerating or decelerating .
The problem has been building for a long time. It began very subtly. It felt like being buffeted by wind behind a big truck. But it was getting worse.
Things got worse after I changed the valve cover gaskets. The intake plenum has to be removed to get to the right valve cover. When I removed the plenum I found the port for the EGR valve completely plugged with carbon and the intake was filthy with oil. After the parts were cleaned and reassembled the truck just seemed to miss even more. It starts easy and usually surges a couple of times and then idles just fine. It accelerates ok although it shifts a little erratically and sometimes hard. It does occasionally knock but not all the time. The miss is most noticeable between 35 and 45 MPH with the throttle just barely open but I can now feel it at any cruise speed with very little throttle.
With a simple code reader the first code I got was a 31. I checked out the EGR position sensor with an ohmmeter and found the resistance too low. So I replaced the EGR position sensor. No change. After that I got a code 34. I removed the EGR valve and re-cleaned it. The valve moves properly from 1 to 5 inches of mercury and air flows through it like it’s supposed to so I put it back on. I checked out the air inlet temp sensor, the coolant temp sensor, the throttle position sensor . I also checked the compression. (170-180PSI each cylinder) I replaced the spark plug wires and cleaned the plugs. (Bosch platinum 2) The distributor cap and rotor are nearly new and look fine.
Next I thought I might be getting a lean mixture though the idle control valve. Although it checked out electrically I thought the valve seat may be worn out so I replaced it. At the same time I replaced the oxygen sensor as a precaution (It had at least 75,000 miles on it.)
So now I’m getting a little nutty and I replace the MAP sensor. I’m not really sure why now.
The last thing I did was tee in a vacuum gauge at the EGR diaphragm and took it for a drive. Cruising at 60MPH the vacuum at the diaphragm was 3.75 to 4.00 in. Hg. I know the valve works at that much vacuum but the engine still misses.
To end this all up, the EGR system checks out fine and functions as it should. Why am I still getting a code 34 and why is my engine still missing at cruise?
The problem has been building for a long time. It began very subtly. It felt like being buffeted by wind behind a big truck. But it was getting worse.
Things got worse after I changed the valve cover gaskets. The intake plenum has to be removed to get to the right valve cover. When I removed the plenum I found the port for the EGR valve completely plugged with carbon and the intake was filthy with oil. After the parts were cleaned and reassembled the truck just seemed to miss even more. It starts easy and usually surges a couple of times and then idles just fine. It accelerates ok although it shifts a little erratically and sometimes hard. It does occasionally knock but not all the time. The miss is most noticeable between 35 and 45 MPH with the throttle just barely open but I can now feel it at any cruise speed with very little throttle.
With a simple code reader the first code I got was a 31. I checked out the EGR position sensor with an ohmmeter and found the resistance too low. So I replaced the EGR position sensor. No change. After that I got a code 34. I removed the EGR valve and re-cleaned it. The valve moves properly from 1 to 5 inches of mercury and air flows through it like it’s supposed to so I put it back on. I checked out the air inlet temp sensor, the coolant temp sensor, the throttle position sensor . I also checked the compression. (170-180PSI each cylinder) I replaced the spark plug wires and cleaned the plugs. (Bosch platinum 2) The distributor cap and rotor are nearly new and look fine.
Next I thought I might be getting a lean mixture though the idle control valve. Although it checked out electrically I thought the valve seat may be worn out so I replaced it. At the same time I replaced the oxygen sensor as a precaution (It had at least 75,000 miles on it.)
So now I’m getting a little nutty and I replace the MAP sensor. I’m not really sure why now.
The last thing I did was tee in a vacuum gauge at the EGR diaphragm and took it for a drive. Cruising at 60MPH the vacuum at the diaphragm was 3.75 to 4.00 in. Hg. I know the valve works at that much vacuum but the engine still misses.
To end this all up, the EGR system checks out fine and functions as it should. Why am I still getting a code 34 and why is my engine still missing at cruise?
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Joined: Apr 2007
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From: st.thomas
my 92 is doing the same,,this 302 feels like a bad miss at street speeds,,did everything yu did and no diff. lm gonna pull throttle body off and clean and maybe that will help,,works perfect at highway speeds, no miss ,
