1991 F-250

HEKIII

MEMBER
1991 FORD F-250
V8
2WD
MANUAL
140,000 MILES

I have a 1991 Ford F250 that I bought new, 140K original miles. Engine recently started racing at idle. Check engine light was coming on and goind out. Its now on all the time. Put the OBD I EEC-IV scanner on it and am getting a number of KOEO codes. 63, 31, 32, 33, 34, and 81 in that order. Majority of the codes seem to implicated the EGR valve. But I've had the same symptoms once before and it turned out to be the MAP (81). Where should I start here? Where should I first start spending money? It is also possible that this whole thing is being aggravated by a small exhaust leak that suddenly got a little louder

4 Replies

WRENCHTECH

MECHANIC
20,761 POSTS

Start by clearing the codes and drive it until the light comes back on and see how many of those reset and those would be the ones to go after first.

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Monday, August 22nd, 2011 AT 2:54 PM

HEKIII

MEMBER
3 POSTS

Thanks for responding. Reset a couple of times before I posted. The exact same group of codes come back up in the exact same order. Frustrating. I cannot narrow it down. Thought I would ask if there was experience with the same set of symptoms before I started tearing is apart and spending money. What would you go afer first?

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Monday, August 22nd, 2011 AT 3:25 PM

WRENCHTECH

MECHANIC
20,761 POSTS

The 63 and 81 are the ones to be concerned with. The 63 is TPS voltage low and the 81 is MAP sensor problem so the individual circuits need to be troubleshooted to determine the cause. The MAP is a major player in fuel mixture.

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Monday, August 22nd, 2011 AT 3:35 PM

HEKIII

MEMBER
3 POSTS

Again, thanks so much for the response. That's what I was thinking. That TP and ERG could be affected by bad MAP. Had the same symptoms about 6 years and 20K miles ago. Did not check codes at that time but symptoms were exactly the same. Repaced the MAP and all was well. I have a volt meter but I dont have a vacuum pump to ramp the MAP, so I am just going to start by biting the bullet, buying a MAP for $60, and swapping it out.

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Monday, August 22nd, 2011 AT 4:11 PM