After trying EVERYTHING, I could not solve performance problem w/ '88 F-250, 351C. I unplugged EGR sensor and my truck runs much, much better, although running rich for obvious reasons. Does this give anyone a clue as to what else I could try?

 

>After trying EVERYTHING, I could not solve performance
>problem w/ '88 F-250, 351C. I unplugged EGR sensor and my
>truck runs much, much better, although running rich for
>obvious reasons. Does this give anyone a clue as to what
>else I could try?

well what exactly are your performance problems? by the way your motor should be a 351w not a 351c unless someone has swapped engines. anyway have you checked for error codes? i have an 88 f250/351w with EGR trouble too. code 31 i can't seem to solve yet. what have you tried so far? i might be able to help - done a little work on mine and lots of reading but need more info. it can be a lot of different things like your EGR regulator, EGR position sensor, those thin hard plastic vacuum lines get brittle and break/leak. please elaborate.

Rusty.

 

Correct! Windsor. One of those days. Thanks for reply and accept this additional info. Truck runs like mad on cold motor, however, once @ temp. turns sluggish and out of breath. All new filters, pressures checked, new sensors, compression good, injectors cleaned, and on it goes. Now, with EGR sensor unplugged, runs pretty good, although tough to keep idle first couple mins. after morning start.

 

>Correct! Windsor. One of those days. Thanks for reply and
>accept this additional info. Truck runs like mad on cold
>motor, however, once @ temp. turns sluggish and out of
>breath. All new filters, pressures checked, new sensors,
>compression good, injectors cleaned, and on it goes. Now,
>with EGR sensor unplugged, runs pretty good, although tough
>to keep idle first couple mins. after morning start.
Sound as if your are running lean. When cold you are in open loop then iengine heats up and goes int closed loop and then your performance goes bad. Could be the O2 senser.

 

I too would check the O2 sensor. on the EGR, plug the sensor back in and unplugg the vacuume line that runs to the EGR valve. This will dissable the valve but the computer is still able to get a respnse from it.

 

Thanks for relpy. Already replaced O2 sensor. In fact, first replacement was generic from parts store. I was told spec. is specific on this replacement so I ordered new one direct from dealer. No change. Also, this truck has been scoped 3 times and checked specifically for O2 troubles. No change. Additionally, I had back pressure check @ cat. and that is good. Keep the suggestions coming.

 

Well, I'm no 351 expert, but it sounds like the truck likes more fuel, eh? Well then how about a new fuel pressure regulator - these seem to be a common part people are replacing on our years of trucks nowdays with good results (as opposed to all the stuff everyone reports changing with no results). These actually do wear and go bad over time.

FPR's seem to be a common 302 part in need of replacement, but maybe that's because so many people have 302's instead of the 351's.

(this is assuming you've changed out the fuel filter to make sure a line isn't just clogged)

 

Mine has the same problem. I need to get a fuel pressure gauge to test as I think it is a weak pump or failing regulator. Should the pressure be 39lbs at idle and go up on acceleration (vacuum drop)?

 

You know, I don't want to claim this is the end-all, be-all fix these days, but I've been reading a lot of posts lately that claim that the fuel pressure regulator change-out fixed fuel problems that both showed up via a guage, and those that just didn't.

In the short period of time since I wrote that last post above and this one, I found a new post in the Inline Six forum from a poster claiming he got a recall for the pressure regulator in the 1993 six cylinders (I'll go check my post office box tomorrow to see if I got one).

So my claim is only based on the research I've done through this site, and others, where there are tons of Ford parts people commonly replace with no great effects (TPS, EGR, O2 sensor, etc.), but apparently the fuel pressure regulators are really a part that is starting to wear out on our trucks. And apparently it is more of a wear-sensitive part no matter what the engine size.

Somebody posted the stock style pressure reg. was cheap. While the fuel pumps are certainly suspect on higher mileage trucks, the FPR should be the easier of the two to change... and since a lot of people (1987-1996 owners) are changing them out anyway...

But again, this is just a suggestion, so please do some testing.

Best of luck,

 

Thanks for the valuable information. I did have fuel pressure test done with good results, however, I find this fuel pressure thing quite interesting. I will replace and see what happens.

In the meantime, per someone's suggestion, I plugged my egr sensor back in and disconnected vacum line to egr valve. Performance is about same with egr sensor unplugged, perhaps better, and this is acceptable for this truck. Question: What, if any, are long term issues of running with this vacum line removed from egr sensor?

 

Not too sure about the long term effects - perhaps the EGR vavle would seize?

While I really dislike to mix the Inline Six cylinder and V-8 remedies, many I-6 users are using home-made restrictor plates on their EGR's. We have a problem with tkae-off from dead stops - the RPM's actually go down (to like 300-400) instead of going up when we step on the gas and let the clutch out from stop signs. This really was a pain with a manual transmission around town, but I imagine it might be described in sluggish driveability problems as you said if one had an automatic transmission that just accounted for the loss of power.

 

Gamma Driver: can you tell me mote about restrictor plate? ie. orifice size etc.

 

[updated:LAST EDITED ON 11-Jun-02 AT 11:06 AM (EST)]Ok, this is what I know.

Typically, the V-8 owners - primarily 302 owners - report their EGR holes get plugged up with hard residue, and that cleaning out all the EGR and respective manifold holes makes their engines run better. This is why I don't like to recommend, or even mix, six and eight cylinder information. Many owners report that Ford mechanics also agree this is the fact. (so take yours apart and check everything closely)

On the other hand, many I-6 owners have found that we have clear EGR and manifold holes, and that the EGR doesn't seem to adjust for higher mileage engines. Thus it lets in too much exhaust gas, and (I assume) reduces the overall vacuum in the air plenum - plus it doesn't do the air/fuel charge any good inside the cylinders. What we do is buy two EGR gaskets and use one of them as a template on sheet metal. Some of us restrict the flow (like down to a 1/8-inch hole from approximately a 3/4" hole), and some of us completely block it.

Once made, we pull the EGR off, clean the old gasket off, and use the metal plate sandwhiched between the two new gaskets. (I used some high-temp gasket sealant, too).

But different engines accept different amounts of exhaust gasses, and the EGR's for the different engines were made to different spec's, so the I-6 fix is one for the overall poor design of the I-6's engine systems once they get old. I would still tend to look elsewhere on a V-8 based on all the reports from 302 owners, though the fix is a cheap one to try out.

 

So is the FPR something that engine heat could cause to be faulty? Seems like it is a closed loop problem but maybe it is a heat related problem.

 

Your guess is as good as mine. Some systems are made to respond to the heat, and some may respond to it when they go bad.

I just ordered one for my truck and I'll report back when I get it on. (of course, I have different symtoms than those above, but my truck is not starting right when warm, so I've got a few parts I want to replace - perhaps the Idle Air Control valve, too.)