Engine Starting

starting

#1

I have an '89 Chevy Caprice with the small V-8 engine. The engine has developed a problem with starting. The starter engine engages and turns the engine over but it doesn’t always start. In the old days I would have checked the choke but I don’t know where to look for the problem on this “modern” engine. If I hold my foot on the Accelerator pedal while cranking, it will sometimes start. Any suggestions?


#2

Once it starts does it run OK? Any error lights/codes in the computer?


#3

There are no error lights lit. I have not scanned for computer codes since I don’t have a scan tool.

Most of the time it starts fine and always runs smooth without any misfires. When the problem occurs, it starts but runs poorly (slowly), as if starved for fuel or air. If I depress the accelerator, it generally starts but takes 5-10 seconds before reaching the normal idle speed of about 700 rev/sec.

I used it 4-5 times this morning and it started and ran fine each time. Temperatures here in Fl are in the mid-eighties. I’m not sure if outside temerature has anything to do with it!

Thanks for helping.


#4

youshould have fuel injection. you never should have to touch gas pedal to start engine and if you do do this the car should not start . the TPS sensor will tell computer you are already running, do to age I would have TPS checked. auto zone will check this for you. If you have not changed fuel filter do this also. people forget about this filter because it is under car. I would like to see the car company,s put an automatic warning light for this when the miles reach the change milage.


#5

Thanks… I’ll have the TPS checked.

I appreciate your time and comments.


#6

When starting, the engine computer uses signals from the MAF (Mass Air Flow sensor), or MAP (Manifold), TPS (Throttle Position Sensor), and the CTS (engine Coolant Temperature Senser) to adjust the iac (idle air control valve) and the fuel injectors. Carbon and oil deposits in the air intake tract can cause the sensors (MAF or MAP, TPS) to read wrong. The carbon/oil deposits can, also, cause the iac to stick or it’s air passsage to be blocked.
Use an intake tract and carb/throttle body spray cleaner to remove the carbon/oil deposits. You should notice an improvement in start and idle.


#7

Hellokit: Thanks for the thorough explaination of the inputs feeding the engine computer. I’ll get the throttle body spray you suggested and use it immediately.


#8

as if starved for fuel or air. If I depress the accelerator, it generally starts but takes 5-10 seconds before reaching the normal idle speed

Similar to the days of carburetors, when you fully depress the gas pedal in a computer controlled, fuel injected car, it signals the computer to shut down the fuel injectors completely (with a carb, you fully opened the throttle plate/choke to accomplish the same thing). This is a means to overcome a flooded engine. If it seems to help start the engine, I’d be looking at reasons why a leaner mixture helps it to start. Many possible causes; low fuel pressure, bad pressure regulator, leaky injectors, bad input signal from feedback sensors causing too much fuel to be injected, excessive carbon deposits in the cylinders, weak spark etc etc etc.

The first place I would start is back at the basics, especially if they haven’t been done in a while. New plugs and an intake inspection/cleaning if necessary and go from there.


#9

It sounds to me like possible fuel starvation. When you depress the accelerator all the way the TPS is signaling the ECU to widen the injector pulse widths and it’s getting sufficient fuel.

Since this is intermittant, and if it’s throttle body injected, you may have a sticky injector. I thought of a weak fuel pump, but the symptoms for that are usually a bit different.

However, having said that, it could be ignition related. A good tech with a scope could determine that.


#10

I discover the cause of the poor starting problem! It turned out to be a loose negative battery cable. Strange but true.

Thanks for you help.


#11

I discovered the cause of the poor starting problem! It turned out to be a loose negative battery cable. Strange but true.

Thanks for your help.