Dead spot in idle
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Senior User
Joined: Feb 2003
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From: Bronx, New York
Dead spot in idle
I have a 97 expy w/5.4l engine. I have a dead spot in my RPM range at about 1300-1600 under load, or 800-1200 at idle. This only happens at light throttle applications. I have no DTC's in memory, and have replaced a few coils & spark plugs that have failed. I have tried to force the ECM to report a DTC by trying to hold the throttle at the RPM where the engine seems to die, but none have reported. This fact leads me to believe that I may have a bad injector or two, since that would not report a DTC. I used some injector cleaner, but it did not help. I checked my vaccum hoeses, but they looked good. Anyone have any help/insight on this ??? Any info would be appreciated
Hotshot
Joined: Aug 2002
Posts: 12,679
Likes: 15
From: BC, Canada
Dead spot in idle
At the RPM you noted does the engine miss or hesitate or?
MAF and TP problems wont always set a code. If it is more of a hesitation than a miss those are the things I'd be leaning towards.
MAF and TP problems wont always set a code. If it is more of a hesitation than a miss those are the things I'd be leaning towards.
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Senior User
Joined: Feb 2003
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From: Bronx, New York
Dead spot in idle
I used the word "miss" because I thought it fit. I can best describe it as a "dead spot". As the RPM's climb to the mentioned range, the engine sputters as if it were starved for fuel. I guess you have to see it to really get a feel for it. From a rest, If I gently apply throttle the engine smoothly accelerates up until it reaches the RPM mentioned, it then seems to just drop off, dropping back to the lower RPM where it all started. If I accelerate hard, the engine just zips past the "dead spot." I don't know if I mentioned it before, but at idle I get somewhat of a rough idle, the motor normally idles at 800 or so, which is the lower range of where my problem starts. In gear or under load, it does not happen until 1400 or so. Thanks for your help.......
Postmaster
Joined: May 2002
Posts: 3,028
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From: Annapolis, Maryland
Dead spot in idle
I'm not quite sure, but couldn't this also be the fuel filter? If it's clogged, it might "starve" the engine here and there (I think that if your engine is demanding more fuel, then the increased pressure may overcome a clog, whereas the lower pressures wouldn't make it past a clog).
It's worth a shot either way - the fuel filter is relatively easy to get to, and relatively cheap. If you haven't changed it before, then you're probably about due anyhow.
Let us know how it turns out!
XXL
It's worth a shot either way - the fuel filter is relatively easy to get to, and relatively cheap. If you haven't changed it before, then you're probably about due anyhow.
Let us know how it turns out!
XXL
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Senior User
Joined: Feb 2003
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From: Bronx, New York
Dead spot in idle
Ordered the Throttle Position Sensor today.....was only 40 bucks and easy to install, going to check the resistance of my injectors too. They should read 11-18 ohms.......
Postmaster
Joined: May 2002
Posts: 3,028
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From: Annapolis, Maryland
Dead spot in idle
I forgot about the TPS. That would be the next logical step.
Keep us posted.
XXL
Keep us posted.
XXL
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From: Bronx, New York
Dead spot in idle
I changed my Throttle Position Sensor today, and also cleaned my Mass Air Sensor. While I had access, I cleaned my throttle body as well. Nothing helped. I even took care to reset the ECU after working on the truck, but no change. I took ohm readings from the injectors, but they were within OEM standards. PLEASE HELP !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
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Thread Starter
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Senior User
Joined: Feb 2003
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From: Bronx, New York
Dead spot in idle
I checked for vaccum leaks as well as I could, but didn't find any. Is there any way to check the MAF sensor, using an ohmmeter to check the little elements ?
Hotshot
Joined: Aug 2002
Posts: 12,679
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From: BC, Canada
Dead spot in idle
I would assume you could if you had specs for it. You might be able to measure a known good one and compare yours. They would both have to be at the same temperature.
On a scanner we watch the voltage from the MAF.
On a scanner we watch the voltage from the MAF.
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Senior User
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From: Bronx, New York
Dead spot in idle
Okay, I posted this same problem on the 4.6/5.4 engine forum, and someone reccomended I clean the EGR and Idle Air Control valves. Would it be smarter to just replace them , if I have to pull them off to clean anyway ? Does this sound like a logical solution ? HELP !!!
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