Engine/Transmission (1994 - 1998) How can you tell when your P 7100 is going bad...

[cray]

A week ago truck just started acting sluggish, 5th gear wouldn't pull past 2500 revs, now 4th won't pull past 2500 revs and 5th won't pull past 2300 rpm's. When I try to get more revs I get alot of blue smoke and it just stumbles and chokes... ... . kinda reminds me of how it acts on a really cold morning if I don't let it warm up a little. Have not changed fuel filter in a while and I have not checked to see how much fuel pressure I have. Any ideas or suggestions would be greatly appreciated. TIA



Christian

 

[tp0d]

Well, a 7100 pump is definetly not a VP, it will almost never go bad, unless you run dry fuel or gas or something like that.



I would definetly check your fuel filter, its a cheap fix. Fuel pressure is a good next step.



Have you checked the condition of your fuel lines? Might be getting some air into the suction lines which will kill performance. The rubber lines can bleed air in but not fuel out. . Make sure to check your return line real good (way back on the drivers side of the head, about #4-5 cylinder) and also check the SS braid quick connects under the drivers feet.



Have you ever checked the overflow valve? If you have more than 100k, and havent messed with it, you probably need a new one. Theyre not too pricey, a seller listed here somewhere sells em for $42 shipped. Got mine there, good stuff...



Welp, mebe someone else will chime in. .



Ohya, you didnt mention what your boost and pyro numbers were...



-j

 

[nfox]

Low Power

I agree tpOd I would also suggest to get the timing checked to make sure it is at 15* to 16*

 

[Will24]

I'll agree with what the other guys said. Timing is more than likely the culprit, but also check the fuel lines and such also, they are a common problem.



-Will

 

[Joe G.]

You definitly need to know what your fuel pressure is while running down the road. If it's too low the problem is the fuel supply system (most likely an air leak somewhere) or a bad overflow valve. If your fuel pressure is ok then check to see if the timing has slipped.

 

[Lsfarm]

Fuel filter first!

I had a customer with the exact same symptoms come to the shop, he had changed his fuel filter only a month earlier.

After checking many items [I had assumed the filter would be good] I finally narrowed it down to fuel supply.

The one month old filter looked like it had 100K on it. A simple filter change fixed all the problems. He had purchased a bad tank of fuel.



Changing the fuel filter: less than 30 minutes

Deciding the filter was bad: three hours!!



I'd change the filter first, and also check the air filter, mice can build a nest in the filter box overnight and significantly reduce air flow. I've found more than one airbox full of dog food!!. Mice think a bowl of dog food is a supermarket with the doors open and no cashiers.



Hope this helps, Greg L

 

[Jim Fulmer]

I've found more than one airbox full of dog food!!. Mice think a bowl of dog food is a supermarket with the doors open and no cashiers.



Nice post Greg!



12V's can be a little trouble at times, the GF calls mine a Bit**, she's moody and needs attention !



Jim

 

[98slushbox]

tp0d,

Who sells the overflow valve for that price? that sounds like that is one of the best prices i've seen.

 

[tp0d]

98slush:



Had to do a search... found it tho. . these are good people. The price doesnt include washers, but theyre a buck or two more. Sure beats Cummins 98$ price. . I didnt have to file down anything to get the new one in either...



Precision Diesel Injection and Turbo Inc.

888-734-7349

$35 + $7 shipping and handling



tell em you're from TDR



-j

 

[cray]

Thanks ya'll, over 200,000 miles on truck..... never messed with timing or the overflow valve. Will start with fuel filter and checking fuel lines and go from there... ... .



ps..... Anybody around Nashville, Tn doing pump timing ???????????

 

[98slushbox]

Thanks tp0d, I'll have to give them a call.

 

[BigPapa]

Hey cray,



Welcome to the TDR!



Head on over to the "Local and Regional Chapter Events" forum, go to "Southeast", and make your presence known to the my fellow members of the Mid-Tenn TDR.



For the timing, contact Meacham at Cedar City Diesel & Automotive, -- email address removed --, (615) 443-3502. He is the MAN!



Scott

 

[1BadDad]

Hey Greg maybe you should do "stand up" instead of flying! Pretty funny! Just a thought to add to the others... There are two steel lines that bend 90* at the top of your fuel tank, I belive it is called the fuel sending unit. Anyway, my truck had 270K and the supply elbow rusted over the years and created a pin hole leak. the more throttle you give the more fule squirts out! The truck was leaving small puddles of fuel until I noticed and was able to replace it. Dodge dealer 300$ Hope all goes well!

 

[AKramer]

I've got the same symptoms as cray described, so I thouhght I would post a question here.

The blue smoke and the stumbling are the same as his, as well as low supply pressure on my gage. The only thing I don't know is the timing, but could it really slip all of a sudden? I'm running a hose straight from a can into the lift pump and I'm seeing 16psi at idle and a slight surge to 20 when I raise rpm to around 2000 but then it drops off to 10 or lower if I goose it. (blue smoke and stumbling) If I pinch off the return I can get 30psi but it rises slowly. I streched the spring in the return valve to 1/2" as some other posts had described, it made a slight difference, but only a couple of pounds. I have both parts comming for tommrow, (valve and lift pump) just wondering if anybody here had a sugestion, or can tell me if the injection pump failing would act like this? The truck only has 115K on it, I'd hate to think the worst... Thanks in advance!!

 

[Joe G.]

It sounds like an air leak in the fuel heater to me. Take the fuel heater off and see what affect that has.

 

[SFenwick]

My '97 did the same thing...

Hello,

Well, by now you have probably found the problem. If you have not, I can offer a simple probable solution, after I tell you what happened.



My 97 12v progressively became harder to start. (It has 225k miles) It used to start without touching the pedal, but for the last 2 months, I always had to apply slight throttle to start.



I then noticed that when pulling a long hill or passing or winding out 4th, the pulling would just stop at about 2200rpm. It was maddening. Then, when pulling a trailer, if I goosed it at all, the truck would just "fall on it's face" and all but stop pulling. It took about 2-3 seconds to recover.



Sometimes it would act like this and sometimes not. Mostly in the morning, when it was cool, it ran fine. I have a number 6 TST plate in my truck, 4in exhaust, K&N drop-in filter, and I really enjoy it when it pulls hard on acceleration. But it never made much serious power after 2200rpm.



Finally, recently when driving on a fairly long trip (about 300 miles round trip) with no load, I set my cruise on about 63 where I get great mileage. After 100 miles of driving, it would literally not pull the hills with the cruise control on. The pedal would nearly be on the floor and the truck would be like I had run out of fuel. Mind you I carry 90 gallons in the back and 35 in the regular tank. I have PLENTY of fuel.



If I shut the truck off for a little while, it would sorta pull fine to about 2000 and then just stop pulling. Then after some constant-speed driving (still on this trip) it would get to where it would not pull the hills.



This has been going on to a lesser degree for about 4 months. I figured that the #6 plate would be my cure, and put it in about a month ago after replacing my 5-speed transmission (which is another story!).



After reading many of the posts here about this suspicious condition, I figured the following:

1. My main fuel filter canister needed replacing - I had never replaced it from when I bought the truck, used, with about 125k on it. (it has 225k on it now)



2. My overflow valve was blown on the pump.



3. My fuel pump timing was bad or the fuel pump was "going bad".



Here is the conclusion:

I first replaced my fuel filter element in the cannister. It was a mess, but glad I did it. It needed it, but it DID NOT fix the problem.

I finally read some more and found a small "pre-filter" fuel screen under the main filter. When I pulled that off - boy was that a mess. The screen was completely black with fine particle dirt, almost like an oily paste. I cleaned it out with hot water and STP cleaner in the purple bottle.

Let me tell you - what a difference. Feels like a new truck.



Don't forget to clean this little filter screen before you go for the big stuff. It is sorta easy to overlook and O-so easy on the wallet. You just have to clean it.



Sorry for the long-winded explanation, but wanted to make sure it was target on by symptom.

-Shawn Fenwick

 

[Heepdriver]

As far as funny things to find in an air box, I found a bird once or what was left of it. found pieces of him in the turbo and feathers when you blew air backwards through the intercooler.

 

[AKramer]

Shawn, your long winded post is great! I wish I was as lucky as you were, unfortunately I replaced that whole heater setup (and screen) allready because my heater burned up and left a hole in the top where the wires go in. Just a note- the new heater assembly from the dealer had a pinched O ring right out of the box, which of course was a mystery vacuum leak for a while. (imagine how happy I was. . ) I'm still waiting for an overflow valve from the people in michigan. Sure hope that's it... any more ideas?