Need help diagnosing an idling problem . When the engine temp rises from 150 to 200 degrees, usually when I am stuck in bumper to bumper traffic and after the car has been running for a while the idle starts to get very choppy and the car seems to want to lurch forward. When I first start it up in the morning and drive it around with out getting stuck in traffic, no problems, just when the car has been run for a long period of time (about an hour) and I get stuck in the stop and go traffic. If it starts getting choppy, I put it in Park and it idles normally. Then back into drive and it’s choppy again. Short trips are no problem but once it starts getting hot and idling badly, it seems like I have to wait until the next day to drive it again so that it idles smooth. I know when the warmer weather gets here; it will start idling badly a lot sooner.
Car Setup: SB 350 (330hp crate engine), TH 400 Trans, stock converter, Edlebrock 600 CFM carb, Edlebrock Performer Intake, Hooker Super Comp Headers out to Flow Master dual exhaust, 4 core radiator, 17" flex fan, 2 x 14 air filter.
Concerns: The spark plug cap on Cylinder 5 is touching the header pipe...I put some insulation on it to prevent it from melting until I can make a performance dent [img]graemlins/clonk.gif[/img] . The heat in the engine compartment getting into the intake...would it run better sucking in cooler air?
Could be borderline vapor lock. Make sure your fuel lines past the headers and front of the block aren't taking on allot of heat from the engine. Your engine will perform better with cool air. Thicker air in the cylinders makes more combustion.
Oh yah. Check even the path of the exhaust pipes going along the fuel line path. There have even been some guys found the fuel line and return lines got reversed at the tank. Amazing world.
I have a steel line from the tank down the side of the frame where the fuel pump is, then rubber fuel line to the pump and from the pump to the carb. The line from the pump to the carb runs up the front of the block, behind the water pump and on top of the header to the carb. A couple of years ago, I put a Flex-a-lite Black Magic fan in place of the flex fan off of the water pump to cool the older engine I had in the car at the time because it had an over heating problem and I am thinking the problem went away. That fan was only on for a short period before I put in the new engine. I took it out because the thermostat in the fan went and I had to manually switch it on when I saw the engine temp hit 180. That fan blew 2800 cfm and it did a great job of cooling the engine and even cooling where the fuel line runs in front of the engine block.
However, I am still confused as to why it would run choppy in Drive then smooth when I put it in Park?
I think I will reroute the fuel line in front of the engine and try and insulate the steel line along the frame, it does run close to the header. I have no return fuel line. If the problem continues, I might put the Black Magic Fan back in and operate it manually to see if that is the problem. I will also check the spacer between the carb and intake. I am not much of a carb mechanic so if all the other things fail, I will take it to a shop and let them take a look at the carb (Edlebrock 1406).
Thanks for the quick response [img]smile.gif[/img] ; I will let you know what happens.
I put the fiber spacer in and put rubber tubing around the steel line by the RH header that runs along the frame rail. Still get the rough idle around 180 degrees. I noticed that I had some serious vacum when I went to put gas in the tank. I put another cap on that had a vent. I put it in Park and idles fine, put it in Drive and rough idle . The only thing I can think of is the fuel line next to the header, maybe I should route it on top of the frame rail, right now it is about 1/2 an inch away from the header. Then again, the ruber fuel line going to the carb from the pump is touching the lower radiator hose. I don't know, I am stumped, I will try and look at everything again this weekend.
I figured out what the problem was. After putting the spacer and insulating the steel fuel lines and still no luck, I started wondering about the fuel pump. I decided to put in an electric fuel pump and by pass the mechanical pump altogether. That was the answer , I am guessing the mechanical pump was old and when it got hot, it would not put the 5 to 7 psi out. I had the temp up to 210 degrees and it was idling as steady as a rock. Now I just have to figure out how to insulate the electric pump, when I am at idle, I can hear the hum of the pump. I located it between the gas tank and the rear axle. Thanks for all the help, this is an awesome site. [img]graemlins/beers.gif[/img]