[Logan Brouwer]

Hey guys so I've been having a problem with power surges in my 1994 GMC 1500. I don't know if this is relevant or not but my Cat-back exhaust fell off about a week and a half ago due to rusty hangers that broke causing the exhaust flange right behind the cat the break. I was on my way to work about 20 miles away so i pulled over and threw it in the bed of my truck and later that night (I work second shift) I welded on a new flange, bolted and hung my exhaust back on with no problems. a couple days later I started getting a power surge like my fuel filter was clogged. I first started with changing my air filter which was probably long past due because I took my truck to the dunes 6 or 7 times this summer in Michigan. the Air cleaner didn't do anything so I put a new fuel filter in it also. I parked my truck in the garage over night and it wast leaking fuel anywhere which zeros out the possibility of air getting into my fuel line. I have a couple thousand miles on a delco fuel pump so I doubt it is that. I then changed the oxygen sensor and that didnt do anything either. after putting in the new oxygen sensor i thought all was good but now the vacuum line that runs out of the back of my motor to the transmission keeps blowing off causing me to lose overdrive. It has happened twice and I put a hose clamp on it to fix it for now but I dont know if that will be good or bad considering that it keeps coming off for a reson. Is this going to be an easy fix or a trip to the shift shop? I have searched forum after forum and cannot find anyone else who has had this problem. there is about 6,000 miles on a transmission rebuild that happened back in July.

 

[Logan Brouwer]

I Lost 4th gear again on my way home from work today, Vacuum hose is connected still so I do not know what to think anymore. someone out thtere has had to have this problem before please help!

 

[Differently]

When you loose od is it slipping?

 

[Zach Smith]

Hey bud, when rebuilt did it get a vac mod kit installed? I believe they are all CPU controlled OE anyway. The 700 however could swing both ways however... Har har.
Anyway, the 60 OE OD would be cycled by the ecu and would be a ground switch (I believe white) wire coming up from trans, and also easy to find where the main bundle splits at the fire wall near the brake master.

 

[Differently]

Also, did a shop do the rebuild? I would think with only 6000 miles you would have some sort of warranty.

 

[Logan Brouwer]

When you loose od is it slipping?

No It isnt slipping at all. It will just downshift out of 4th and stay in third gear. let off the gas to coast and it will calm down to about 1500 RPMs and then when I get back on the gas it will go right back to the top of third where it was. Trans was rebuilt at a shop and I'm thinking im going to have to pay a visit tomorrow.

 

[Logan Brouwer]

Hey bud, when rebuilt did it get a vac mod kit installed? I believe they are all CPU controlled OE anyway. The 700 however could swing both ways however... Har har.
Anyway, the 60 OE OD would be cycled by the ecu and would be a ground switch (I believe white) wire coming up from trans, and also easy to find where the main bundle splits at the fire wall near the brake master.

going to have to check wiring then thanks for the tip. I do not believe that a vacuum mod kit was installed, but will have to check the paperwork to see if that is true.

 

[Zach Smith]

I would just visit the shop like different says...in other words don't touch unless you really feel you need to...just bring it to them, ask them to ask you, before any work...

 

[Zach Smith]

Also...do you have loss of power...like pulling a hill?

 

[Logan Brouwer]

Also...do you have loss of power...like pulling a hill?

Yes i have a loss of power like that. and also it surges when accelerating from a constant speed. also when in gear and at a stop light it idles very low if i stay in gear but if shifted to neutral it will idle fine.

 

[Zach Smith]

Check engine light? Po420 or similar?

 

[Zach Smith]

Your tans may be doing what it is supposed to, downshifting for lack of power compensation.

 

[Logan Brouwer]

Check engine light? Po420 or similar?

No engine light but haven't plugged in a reader to see if it's throwing codes.

 

[Zach Smith]

Yeh, these older dogs, don't have much to say sometimes anyway.. But the loss of power, low idle and surging suggest, trans may not be the first place to look...what rpm do you idle at in Park...Neutral? Where do you idle in gear?

 

[Logan Brouwer]

Yeh, these older dogs, don't have much to say sometimes anyway.. But the loss of power, low idle and surging suggest, trans may not be the first place to look...what rpm do you idle at in Park...Neutral? Where do you idle in gear?

the park and nuetral idle is pretty normal around 1000 to 1100 Rs and when in drive at a complete stop tach needle reads around 200 but i don't think its the most accurate, also can tell it is idling slow watching the oil pressure go down to about 20psi when at normal idle sits at about 35-40psi. I'm just an 18 year old kid who wants his truck fixed and can't figure it out haha

 

[Zach Smith]

1 to 11k is pretty high for idle bud. Have you modified this in some way, or has it just always been? Mine is a bit high at 7H but I like it there for various reasons. We might have a vacuum leak going on here...what do you have for tools?

 

[Zach Smith]

BTW...your here, listening and hopefully learning. Nothing wrong with being 18, I was once too....a while ago

 

[Logan Brouwer]

BTW...your here, listening and hopefully learning. Nothing wrong with being 18, I was once too....a while ago

I have had the tuck since August of 2016 and it has always been that way

 

[Zach Smith]

Tell me about this vacuum line, where exactly does it come from...go to, pics are great also...

 

[fatboy022]

the 700 or the 4l60e does not have a vacuum line going to it . unless someone put in a modulator in it to eliminate the epc .. and that is NOT part of a standard rebuild ... im with zach .. where is this line coming from and running to . the only trans with the vacuum was the 350 and 400