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99 Acura not re-starting in heat

I have an Acura TL 1999 that has started having trouble re-starting in hot weather. I’ll drive it to a store and when I get back in to go home, it has trouble starting. If it does start, I have to pump the gas to keep it going and it takes it a few minutes of driving to stop shaking. It’s only on days that are 75+ degrees outside. We had a mechanic tell us a few months ago (right after getting the transmission flushed by the dealership) that the transmission is on its last leg and will need to be replaced soon. Are the two problems related at all? We’re trying to decide if it’s worth putting the money into it to fix it at this point.

Starting problems are totally unrelated to your transmission.
Hondas of that era (your Acura is, after all, a Honda) do have known issues with their transmissions, so it is possible that you do have trans replacement in your future, but–related to a starting issue? Ummmm…no.

As to the root of the starting problem, what you describe is typical of a Honda that needs to have its main electrical relay replaced. This component is located underneath the dashboard, and when exposed to high interior temps, it will typically prevent electricity from flowing to the fuel pump–hence, no start. Open the windows, air the car out for awhile, and it might start, due to a drop in interior temperature.

Replacing the relay is a relatively cheap and easy fix, and is also well-known to any mechanic worth his salt.
If your mechanic is not aware of this Honda issue, then I would question his expertise.

Yeah, the problem with the main fuel relay is well known, or so I thought. So it always surprises me when someone reports that his professional mechanic is either completely stumped or is advising a far more expensive repair when this issue comes up.

The problem might be with vapor lock. If the fuel pump shuts off and the fuel system doesn’t hold residual fuel pressure the fuel in the fuel rail(s) can start boil from the engine heat. This then makes the engine very hard to start and if it does start the engine can run rough.

Have someone check the fuel pressure to see if the residual fuel pressure is within specs.

Tester

I thought the main relay problems were gone by the late 90s, but it’s obviously easy to figure out & not a big investment of $$ or time to look into it.

I was going to add the possibility of heat soaked ignition components. You run the car & park it on a hot day & lots & lots of heat builds up under the hood. This can, for example, send an iffy ignition coil over the edge until you drive enough that it cools down.

Overall my bets would be on this or on a fuel pressure issue, as Tester noted.

Is the check engine light flashing while this is going on? It must be on. Don’t drive it if it’s flashing. Have the codes read and post them. Many auto parts stores read them for free. The codes look like “P1234” and folks here won’t care what anyone said about the codes - just what the exact codes are.

Tester- I thought vapor lock when away with the mechanical fuel pump/carb… I have been told its not possible on a fuel injected car due to A) pump in the in the tank in most cases B) higher pressures they use…

There are probably multiple meanings of the actual term “vapor lock” these days. A fuel pump won’t vapor lock anymore being that it is in the tank and submerged in liquid gasoline. And the “anti-vapor lock” characteristic on fuel injection systems is heavily predicated on the pressure preventing that. The problem comes in when the pump/check valve do not maintain the pressures. Fuel rails are really thin and if not pressurized there’s no reason the fuel in it can’t turn to vapor.

I happen to know that some version of this happens with my car. I know that when its hot & I shut it down I almost immediately lose fuel pressure. I have watched that on a pressure gauge. I also know that I often get mild rough running on a hot restart and have a very audible gurgling from underneath my back seat (the fuel tank). I have always assumed that is either fuel vapor or air or whatever running back into the tank through the return line. After about 30 seconds, the sound stops & the car runs well. Is it old-fashioned carb & external pump vapor lock? No. But its something in that family of stuff.

(I have a fuel pump from a parts car in my garage. I’ll put it in one of these days).

Cigroller,

It doesn’t matter if the gas boils in a carburator, fuel pump, or in the fuel rails, it’s still called vapor lock.

See what it’s called when a hot fuel injection system has a low residual fuel pressure here. http://www.aa1car.com/library/2003/us60324.htm

Tester

Tester, Thats cool. I was agreeing with you. All I was saying is that I don’t care what “X” person calls “vapor lock.” That includes what aa1car or any other source calls it. On older external & mechanical pump/carb systems the basic problem is that once the fuel vaporizes the pump can’t pump anymore b/c it can’t pump vapor. So it ceases to be able to move fuel. Nowadays that part isn’t true. The pump is electrical and in the tank. The fuel in it won’t vaporize and it can always pump. But the fuel can still vaporize in the rail, as you said, and cause problems the one described here.

Your description was correct. gsragtop expressed skepticism. I defended your interpretation. But I won’t require anyone to call it “vapor lock” in case they somehow want to reserve that for the slightly different, older kind of problem.