sort of stumble at idle

[LT4man]

LT4's are just too darn cool for an EGR valve. They are so clean and efficient they don't need one.

JimBobC4!!!!! You win the prize!!!!!

Technically speaking, the intake and exhaust valves overlap so significantly with the reprofiled LT4 camshaft to render the use of an external Exhaust Gas Recirculation valve utterly useless!

This overlap contributes to the high revving capability of the most advanced and most unique small block engine ever designed and built by the Bow Tie Guys!

Next question, class!

SAVE THE

 

[Toms007]

Issue comes back with a vengance

OK, today I take the Vette out to run back where I grew up for a funeral. All the way down she runs pretty good, maybe a touch warmer than usual (200-205). I get about 140 miles from home and going through a town the little stumble at idle in gear starts again (not bad but I can feel it). I take her on in to the in-laws (another 25 miles or so) and she runs ok. After the funeral (about 4 1/2 hours later), I get back in to head home, the little stumble is back. No biggie when I have to stop I just kick it in neutral, then once I get it going again she's alright, but as I get further down the road the worse she runs rough, pinging, bucking at times. And when all this is going on the temps start to climb (up to 230). Once I get it up to cruising speed she kind of smooths out, but don't step on the gas (as in passing) as it starts pinging and bucking and the temps start up again. Once I get in to a cruise mode the temps will come down some (215 -220). I have made it home (170 miles) and she is running like cr@p.

What's the verdict? No lights came on during the trip, but I will go out and see if it has any codes set later.

 

[gmjunkie]

What's the verdict? No lights came on during the trip, but I will go out and see if it has any codes set later.

Maybe check the EGR Tom!!Maybe the screen slipped on you putting EGR back on,I had that happen to me once and it started sucking air between the gaskets!

 

[LT4man]

Is this a Multiple Choice Test??
1.You always use Name Brand Quality Fuel.(Moble/Exxon,Chevron/Texeco,Shell,exc.)
2.You never store your car unless it has a full tank.
3.You drive your car Daily,if weather permits.
4.Your car is always properly warmed up.
5.Your car is always properly tuned.
6.Your car is always properly serviced.
7.You'd Never let a MoonShine toting HillBilly drive it.
8.Your car is always locked in the garage with the keys and fob in it and it don't go anywhere!!!
Damn Gregory,Sorry I just couldn't resist that!!

junk: You get a prize because of the creativity you used in formulating the answers to the test.

Wanna know what kind of prize???

THE BOOBY PRIZE, BUDDY!!!

You didn't see that comin', did ya?

SAVE THE

 

[LT4man]

OK, today I take the Vette out to run back where I grew up for a funeral. All the way down she runs pretty good, maybe a touch warmer than usual (200-205). I get about 140 miles from home and going through a town the little stumble at idle in gear starts again (not bad but I can feel it). I take her on in to the in-laws (another 25 miles or so) and she runs ok. After the funeral (about 4 1/2 hours later), I get back in to head home, the little stumble is back. No biggie when I have to stop I just kick it in neutral, then once I get it going again she's alright, but as I get further down the road the worse she runs rough, pinging, bucking at times. And when all this is going on the temps start to climb (up to 230). Once I get it up to cruising speed she kind of smooths out, but don't step on the gas (as in passing) as it starts pinging and bucking and the temps start up again. Once I get in to a cruise mode the temps will come down some (215 -220). I have made it home (170 miles) and she is running like cr@p.

What's the verdict? No lights came on during the trip, but I will go out and see if it has any codes set later.

Tom, the temp increasing while this problem is happening tells me the fuel mixture is leaning wayyyyyyyy out.

I agree with junk. Check the gaskets at the EGR valve.

I would also attach a fuel pressure gauge to the fuel rail and see where your pressure is. All of the LT1/4 engines LOVE lots of fuel pressure. 41 to 47 pounds of the stuff. If you can, attach the gauge to your hood with some tape where you can see it from the driver's seat. Take it for a ride (not too far from home!) and see where the pressure is.

Lack of enough fuel pressure would make the mixture lean and cause all the bucking you are experiencing.

SAVE THE

 

[Toms007]

OK Junk and Gregory, I'll check those things tomorrow....one more item that might have an impact on things.....when i left this morning it was 68* outside, by the time I got to my destination it was 90*...when I left to return home and all the way back it ranged from 99* all the way up to 107*. Not sure if this has any bearing.

 

[Toms007]

OK here's where we are....

I removed and reinstalled the EGR, I had used a bit of sealer to hold the two gaskets together with the screen in-between. Everything looked good so I put it back together.

I put a fuel pressure gauge on and turned it to the "ON" position, I got a constant 42PSI. Fired it up, fuel pressure is pretty much the same. Still bucking idle in gear, not real smooth in neutral. As I rev the engine the fuel pressure may vary for a split second as far down as 36psi but no higher than 44psi, I didn't actually take it for a drive as it was bucking pretty good, however if you guys feel I need to, I can.

I checked for set codes, I now have a history code 43, nothing in the current.

 

[LT4man]

OK here's where we are....I put a fuel pressure gauge on and turned it to the "ON" position, I got a constant 42PSI. Fired it up, fuel pressure is pretty much the same. Still bucking idle in gear, not real smooth in neutral. As I rev the engine the fuel pressure may vary for a split second as far down as 36psi but no higher than 44psi, I didn't actually take it for a drive as it was bucking pretty good, however if you guys feel I need to, I can.

I checked for set codes, I now have a history code 43, nothing in the current.

Tom, according to my FSM, your engine needs 41-47psi fuel pressure at ALL times.

The only things that would cause it to dip to 36:
1. Restriction in line (ie. clogged fuel filter)
2. Defective fuel pump (ie. took a dump!)
3. Leaking fuel injector(s) (how old are they?)

As far as driving. As mentioned earlier, only for a SHORT distance! IMHO, I would keep it in the driveway!

Hope this helps!

SAVE THE

 

[LT4man]

OK Junk and Gregory, I'll check those things tomorrow....one more item that might have an impact on things.....when i left this morning it was 68* outside, by the time I got to my destination it was 90*...when I left to return home and all the way back it ranged from 99* all the way up to 107*. Not sure if this has any bearing.

A border-line fuel system will react proportionately to extremely high ambient temperatures. The temperatures will cause an engine to run hotter and the hotter engine will lean out the mixture. Also, lack of proper fuel pressure will lean out the mixture. Without the exact correct fuel pressure, one will experience symptoms of bucking, hesitating, missing & backfiring.

SAVE THE

 

[gmjunkie]

OK here's where we are....

I removed and reinstalled the EGR, I had used a bit of sealer to hold the two gaskets together with the screen in-between. Everything looked good so I put it back together.

I put a fuel pressure gauge on and turned it to the "ON" position, I got a constant 42PSI. Fired it up, fuel pressure is pretty much the same. Still bucking idle in gear, not real smooth in neutral. As I rev the engine the fuel pressure may vary for a split second as far down as 36psi but no higher than 44psi, I didn't actually take it for a drive as it was bucking pretty good, however if you guys feel I need to, I can.

Tom,I think you have a fuel pump getting ready to Take a Dump or a Plugged Fuel Filter!!Lt1's and Lt4's really Like Good fuel pressure!! A L98 can run Good with less than 40,but LT1's and LT4's Won't!!

 

[LT4man]

Tom, H43 is Knock Sensor.

With all the pinging and knocking around, I am not surprised this code was set!

SAVE THE

 

[Toms007]

OK, so should I go ahead and put in a new fuel pump? Injectors are new, fuel filter was replaced in 05 when we were in Bowling Green for CruiseFest 2 about 18K miles back. Of course if I replace the fuel pump I will replace the filter too.

Suggestions on fuel pumps. I know Junkie will say GM but I don't have a GM dealer within 40 miles, do I go ahead and order one from GMparts Direct or someplace else? Part #?

BTW, thanks guys.

 

[gmjunkie]

OK, so should I go ahead and put in a new fuel pump? Injectors are new, fuel filter was replaced in 05 when we were in Bowling Green for CruiseFest 2 about 18K miles back. Of course if I replace the fuel pump I will replace the filter too.

Suggestions on fuel pumps. I know Junkie will say GM but I don't have a GM dealer within 40 miles, do I go ahead and order one from GMparts Direct or someplace else? Part #?

BTW, thanks guys.

No Tom,I don't have a problem with Carter,Bosch,Airtex or other Name Bands on a fuel pump!!I'd rather have a AC,But I think the only it comes is with the whole sending unit!!And it's just too Damned much $$$

Edit : I just looked on GMPD and it's not that bad!!

CLICK!!

The last AC I bought was only offered with the whole unit,Maybe they figured out that everybody was getting them somewhere else and split them up!!

 

[Toms007]

I ordered one from Superior Chevy (in Kansas City) $89 then I went ahead and ordered the basket screen filter that goes with it $35. So for around $125 + shipping it should be here Friday.

 

[Toms007]

I did get the new FP/strainer and fuel filter yesterday...just too late to try and install. Right now I am working on a computer(desktop, not automotive) and one of my daughters' from KC and family are here for the weekend, so I don't know if I'll get to the install today or not.

 

[Toms007]

Alright I have the new fuel pump/strainer in, unfortunately no change in the rough idle/bucking. Fuel pressure reading are the same as before. I have a new fuel filter that I am going to try and get changed out. It's a real PITA to get to even with the lift.

 

[Toms007]

I got the filter changed out too, while doing so I found that the #8 plug was loose so I tightened it up as well. With all of these things changed, replaced or fixed I am still in the same boat. Still runs rough, no power when I step on the gas (bogs down actually), has "popped" (or back fired) through the TB a couple of times. I am now at a point where I don't know which way to turn.

Suggestions please!

 

[scotch1]

Hi everyone.
Just a suggestion. I had a similiar problem, and discovered that I had a bad tank of gas. I dumped in some additive and the problem went a way.

 

[LT4man]

Tom, the low fuel pressure problem is being caused by a mechanical malfunction.

Do you have the FSM? What do they say about the fuel pressure regulator on the back of the fuel rail?

I am working on a deported Mazda Protege right now. Otherwise I would look up the info. :L

SAVE the gosh darn

 

[garyg]

adventures of Tom94

Hi all, I have been following the adventures of Tom94. I also have been conversing with the guru GMJunkie. My 88vette starts right up but won't hold an idle ( replaced air filter, fuel filter and fuel pressure regulator ). I get no code readouts other then 12. You suspect dirt blocking either the EGR or the IAC valves ??? According to my Vette GM service manual an EGR problem causes "stops after cold start", "engine stops at idle after deceleration" and "rough idle".

Does this make any sense? frustrated !!!