Firstfives.org

Could a distributor cause the on/off, jerky throttle response ?

Slight throttle sluggishness ( bogs a bit then catches ) when cold. When warm o.k., runs clean, accelerates well.

But working the gas pedal, tapping it, causes noticeable bouncing. Way more sensitive than my '79.

Switched AFM, new fuel pumps, pressure regulator, plugs, cold start relay, checked vacuum lines, throttle switches, new pedal bushings.

I have 1980 auto with what seems to be the same issues. Cold starts okay, idle 1200 rpm for 4-6 seconds. Warm up: low rpm idle (near stall), bogging while driving. Temp gauge crosses 1/4 line drivability improves. By normal operating temperature car runs great. Replaced all 4 sensors on thermostat housing. Temp sender to gauge, cold start, temp sender to ECU and temp activated vacuum to distributor. I believe that the ECU is not receiving the correct impedence info from the ECU temp sensor or ECU getting good info and not telling the fuel injectors to spray fuel longer which is how L-Jet richens the mixture. When engine reaches operating temp, O2 sensor takes over info to ECU and car drives great. After reading L-Jet articles and finding ECU connector pin numbers (pin 5 GRND, pin 13 Temp impedence) I plan to test sensor wires to ECU. If wires good than ECU is bad and hope I can find a good used one. Sorry for the long note but this one issue has been bugging me for a long time. Will post results.

My main obsession is the bouncy throttle, cold, warm, but I'm interested.

I can drive the drat thing just by paying attention to being smooth on the pedal or feathering rev up to move off when cold, but it's not right.

That's the game. Man 1, machine 0.

pmaronoff wrote:I believe that the ECU is not receiving the correct impedence info from the ECU temp sensor or ECU getting good info and not telling the fuel injectors to spray fuel longer which is how L-Jet richens the mixture.

You are correct in your assumption since the only control over warmup (between cold start and operating temp.) is the coolant temp. sensor enrichening the injector spray through all their phases (idle, accelerating, WOT) of operation.

There is a flow to electricity from + to - and anything that disrupts the path will lead to malfunction (or worse).

The wiring for the sensor is an electrical path to and from the ECU regulated by a coolant-actuated resistor on the sensor. + is the connector on the sensor and the wiring lead to the ECU.

There is a ground for this path located on the right side intake manifold nearest the firewall. It grounds through the engine ground to the battery (-) through the big braided strap. All of these connection points will affect the integrity of that signal (and some other quirky side problems) causing an erroneous mixture (usually lean).

Of course, this assumes your coolant is circulating properly for the sensor to accurately take the engine's temp.

I've been ranting on this for (at least) this long.

T.Hanson wrote:Could a distributor cause the on/off, jerky throttle response ?

Yes, but since it's gear driven, only excessive wear would likely cause your symptom, but while you're chasing, check the operation of your vacuum advance. Unplug the hose from the intake manifold to the biscuit on the distributor (and plug it). Attach a temporary piece of vacuum hose to the advance orifice that is long enough to conveniently stand on the right side of the engine and using your mouth and tongue (not kidding) suck on the hose (doesn't take much) after you start the engine to see how a vacuum affects the advance diaphram at idle. Use your tongue to temporarily seal the end so it holds the advance. After a couple of trys you should be able to smoothly advance the timing and the idle will rise (and fall when the vacuum is not present). Or if there is a problem with the advance, you will be able to duplicate the jerkiness you experience.

Try that.