Rough Idle

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Feb 27, 2003 | 06:37 PM

Rtpjunior

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From: Bronx, New York

Rough Idle

My truck has had a rough idle lately, along with a "dead spot" at about 1000-1500 rpm. At idle, the motor shakes slightly. While revving up slowly, the motor "hiccups" (for lack of a better word), around 1000-1500 rpms. If I rev quickly, it doesn't happen. I am lucky enough that my wife works for a Ford dealer, so one of the techs put my truck on the diagnostic machine. It showed cylinders 5 & 6 were dropping off in the rev range I specified. I changed the coils and plugs for 5 & 6, but it didn't help. I was thinking maybe an injector ??? Any info would be a great help. All the advice I have received so far has been Excellent, far better than the "Professional" techs at my wifes' dealership. By the way, I have a 97 Expy 4 X4 with a 5.4 engine.

Feb 27, 2003 | 11:01 PM

Racerguy

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From: BC, Canada

Rough Idle

Does your wife get a good deal on work done where she works?
Will any of the guys do her a favor and take a quick look at it?
If so, I think it would be good to get them to hook up WDS and watch the power balance and see what it shows. They could also do a Datalogger display and see what happens to the MAF, TP, INJPW, SHRTFT etc at the rpm the problem happens at. They could also check for vacuum leaks while watching the SHRTFT and maybe do a relative injector flow test. Have you tried running any injector cleaner in the tank?

Feb 28, 2003 | 09:54 AM

Rtpjunior

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From: Bronx, New York

Rough Idle

I have tried using fuel injector cleaner, but have had no improvement in performance. My wife does get a break on service, the only problem is the techs who work there are IDIOTS !! All they know are brake jobs and oil changes!!! I am not familiar with the terms you used, but when the tech hooked up my truck, he had a laptop-sized touch screen machine. He displayed a screen that had individual line-graphs for each cylinder, and you could clearly see where #'s 5 & 6 would drop off, at the exact time the motor would shudder. His best guess was the coil packs, which I changed. I have changed a few of the coil packs already, #7 & 8, which got wet when one of the Morons at the dealer decided to pressure wash my motor after he spilled antifreeze all over the place during a flush and fill. Please let me know a little more about the tests you specified, and I'l l try them, Thanks...........

Feb 28, 2003 | 10:45 AM

mikevincelli

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Rough Idle

Hi,
I have had somewhat the same problem with my 97 expy 5.4. 90K miles. I have a very good engine tech. freind that looked at it and said it was the EGR valve kicking in, that caused the rough idle. He said not to worry about it.

Hope this helps.

mike vincelli
97Expy 5.4
K&N air filter
Mass Airflow sensor
Bosch +4 plugs
Magnaflow muffler
Jet Chip

Mar 1, 2003 | 06:39 PM

Rtpjunior

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Rough Idle

Thanks for the reply, but if it was the EGR valve, all cylinders would be affected. The test only showed dropoff on #'s 5 & 6.

Mar 1, 2003 | 09:08 PM

Racerguy

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From: BC, Canada

Rough Idle

It sounds like they hooked up the WDS to your Expedition. If they know how to use it properly it is a good tool. The power balance looks like a graph that shows how much each cylinder is contributing. The tests I mentioned are ones that would be done on WDS. At home though you could check for vacuum leaks by taking a spray can of carb cleaner such as Carb-Medic and spraying it at where the intake manifold meets the heads, at the vacuum hoses etc. If the idle changes at all with the carb cleaner you've found a leak.
Did you change the plugs and coils at the same time? It's possible that a bad coil fouled the plug. I'd be inclined to replace the 2 plugs again.
You can do your own power balance test at home by unplugging each fuel injector one at a time with it idling. They should all make the same difference to idle speed and smoothness. If you swap around the coils from a couple good cylinders to #5 & 6 you should be able to tell if it made any difference that way.
Those are the things I'd try first. Let us know if anything helps.

Mar 2, 2003 | 09:08 AM

Rtpjunior

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From: Bronx, New York

Rough Idle

Thanks for the help, I'll try the carb cleaner first. I replaced the coils and plugs on #'s 5 & 6 at the same time. Do you reccomend replacing the injectors ? I can get a set of 8 Bosch (aftermaket) for about $175. Oem's are like $100 each. I can install them myself, I have the Ford shop manual. I have over 100k on the truck, and I am thinking that the injectors have gone past their service life.