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post #1 of (permalink) Old 12-30-2001, 09:47 PM
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loosing power on the highway

Recently I have noticed what seems to be large lack of power on the highway in overdrive. The truck studders like it is in too high of a gear. It used to occur only on steep grades at about 65 mph. I would simply drop out of OD manually until the top of the hill. This didn't really bother me, but now it happens a LOT more often and on even less steep inclines. And sometimes will also studder for a little bit just after a hill (on the downside) when I put it back into OD.

I turn about 1750 in OD at 65 mph with 3.55 gears pushing 31" tires. Is this RPM low? It has always run smooth at this speed untill recently. It is an 86 302FI with an AOD trans. 107K on the engine. Everything is pretty much stock.

All of the exhaust is recent except the cat (it may be original) Could an old cat cause a choke like this? Any ideas or recomendations to bring back power on the highway? thanks.



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post #2 of (permalink) Old 01-02-2002, 12:59 AM
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Re: losing power on the highway

Check the air filter, fuel filter, & spark plugs. Then try to figure out how much slop you have in the timing chain and see how far off the ignition timing is.


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post #3 of (permalink) Old 01-02-2002, 02:37 PM
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Re: losing power on the highway

I had the exact problem you described. I have a '92 Bronco XLT with a 302ci and 4EOD trans. I was starting to think I had an overdrive problem because of the symptoms you explained. I went back and started checking everything I had recently done to the engine and drivetrain. Bottomline... I pulled the spark plugs and found the #8 cyl. plug pretty well burnt up around the electrode and its insulator. I checked the resistance of the plug wires with the the values in the maintenance manual (Haynes)and found my #8 wire was way over the >5k ohms in the book. I replaced the wires with some lifetime warranty Bosch wires about 2 months ago and it's been running great since.

I know it may sound hard to believe, but it fixed what I thought was a tranny problem.

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post #4 of (permalink) Old 01-03-2002, 03:56 PM
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Re: losing power on the highway

Thanks for the suggestion. I will look into that spark plug idea of yours. Sounds like it might be the same thing... my first thoughts were tranny problems as well, but I've decided its gotta be the engine. It would be nice to find the problem is an easy fix like that! I know I have had troubles with the plugs and wires before. If I'm not mistaken, they were replaced not too long ago and I did notice an increase in power at the time. I'll check my receipts to find out when I did that. If it turns out to be the same/similar issue again, then there's probably another root this problem.

Also, the filters are ok. I have not ruled out the timing suggestion, steve83. A friend of mine had a dodge with a serious lack of power on the highway (couldn't get above 55) and it turned out to be timing related. Although I think his was also a problem with the computer? not sure about that

thanks again
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post #5 of (permalink) Old 01-03-2002, 08:49 PM
 
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Re: loosing power on the highway

Make sure all your wires are plugged into the spark plugs. I recently drove 20 some miles on the freeway on 7 cyclinders and I just couldn't figure out why it was struggling to cruise in 4th gear (yet alone OD) and why it was shaking so bad. When I got home I found one wire completely hanging not connected (someones idea of a joke or something). Anyways, both my motor mounts are shot now along with my exhaust (it leaks for who knows what reason). Yeah I know I'm retarded.


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post #6 of (permalink) Old 01-03-2002, 11:21 PM
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Re: loosing power on the highway

The one thing I didn't mention the first time is... when I first found the bad plug, I replaced it hoping it was just a defective plug. It ran okay for a month or so after that and then started up with the same symptoms. I pulled the #8 plug again and, low and behold, it was tore up again. That's when I found the wire with high resistance and changed it. It's been 2 months since then and the truck is still running as strong as ever.

post #7 of (permalink) Old 01-10-2002, 05:03 PM
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Re: loosing power on the highway

Hey riff-raff, I have a 92 with a 351, but was experiencing the same symptoms you explained. I also was having a back-fire in the engine. I checked the timming, changed the fuel filter changed the air sensor had it hooked up to the scanner and couldn't find anything wrong. I changed the 02 sensor just had it tuned up about 2 months before this started happenning. I was baffeled. Before I changed the Fuel Pump (thinking it may just be getting weak) I decided to get a set of MSD ignition wires to replace the wires from a local parts store. I have a used car lot and have had some problems with parts from them so on a last ditch hunch I changed the 2 month old wires. I then took my truck up to the MTNs. near Las Vegas and had absolutely no problem what so ever. It's been about 1 month and 4 different trips and still runs smooth. I hope this will help. P.S. I also had my tranny rebuilt just before the tune up. I took it back 3 times and they said it wasn't the tranny. I guess they were right. I have over 150,000 miles on my engine.

post #8 of (permalink) Old 01-19-2002, 01:10 AM
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Re: loosing power on the highway - UPDATE

Thanks for the suggestions. I've gotten around to checking out everything. Nothing seemed to be wrong with any plugs, wires, filters, etc... I didn't dive as deep as to investigate a timing issue though.

While I had the hood up I figured I'd top off the fluids: The radiator was down considerably... About 2 quarts! [img]/wwwthreads_images/icons/blush.gif[/img] (oops..) Hasn't been running hot though... unless the temp gauge is broken - that would suck. The oil was almost due for a change, so I did that too. I never have quite as much used oil going back into the containers as I do coming out (old filter is always full) but this time it seemed a bit less used oil than usual...

Not sure what I did, but after the tinkering and changing the oil, the Bronco has been running noticeably better on the highway. Minor inclines that I had to drop out of OD would hold a steady 65 in OD like it used to! Although the real test will come next week running up and down the hills on i84.

Guess I gotta check the oil level more often... [img]/wwwthreads_images/icons/tongue.gif[/img] It does loose some (along with coolant apparently!), but it now seems to have been quite a bit more. This time it may have been down a quart after 2k? bad huh? I change it every 3k, but this time it was at 2200 since I knew I wouldn't have the time to do it later in the month.

On the side - I had also been noticing drive line vibration. I pulled the shaft and the Double Cardan joint was shot to pieces! Oh, it was BAD ... what used to be grease was now a fine powder and the needle bearings were everywhere!!! Anyway, I put a new one in and it runs smooth. I did this about a week prior to changing the oil. It didn't solve the highway problem, but did make the truck run smoother at all speeds in general. I do wonder if the bad joint helped contribute to the lack of power or at least the stuttering tranny like symptoms I had earlier.... hmmmm???



post #9 of (permalink) Old 01-19-2002, 11:27 AM
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Re: loosing power on the highway - UPDATE

Interesting enough, read DAVID post on "IDEL PROBLEMS" (his spelling, not mine)[img]/wwwthreads_images/icons/wink.gif[/img]. Check your ECT sensor as well. I am sure being two quarts low (the Bronco, not you) would create a problem with the ECT and give you performance problems.

post #10 of (permalink) Old 01-19-2002, 04:41 PM
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Re: loosing power on the highway

I had the same problem on my 1990-302EFI. After changing spark-plugs and also redoing the complete ignition system with distributor and coil, nothing changed.

So I brought the Bronco to a shop and did let test the engine with their engine test equipment. Turned out that 2 of the IGNITION WIRES where damaged and burned.

After that it was clear to me, ignition wires can get old. The insulation actually lets moisture onto the wire and it starts to corrode. With the high voltage the wire can burn through and cause loss of power to the spark plug.

So check or completely replace your ignition wires. My suggestions.



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