1993 240 hesitation and almost stalls
 

Hello everyone new to the forum, and new to 240's! i recently just acquired a 1993 240 with 63,000km and in great shape. My problem is I have hesitation on moderate throttle and if the car sits for 20min or longer has a hard time staying running, but will idle fine after a short while. The car will surge forward then just hesitate then surge forward and hesitate again. I have replaced plugs,wires,cap,rotor,TB serviced,new air and fuel filters, also checked for vacuum leaks with my smoke machine and all seems fine. Any suggestions from here??

thanks from Canada

Hesitation
 

Any codes? Could have a dirty mass air flow meter (clean with mass air flow cleaner only) pull back the connector boot to observe corrosion and clean if exist. You may have a faulty coolant temp sensor also 3-4k ohms at 50 f. Fuel pressure should be 43.5psi at the rail.If not remove the gas cap while assistant cranks and pry open door to listen for wirring for transfer pump. Good luck! Hope this helps.

I had a 1-1-3 which i believe is injectors, cleared the code and did not return(this was on from when i first got the 240, then a 2-2-3 which is IAC which I cleaned and cleared code and did not return. I cleaned the mass air, but I did forget to mention that my temp gauge takes a while to move and when it does it rarely gets to a quarter buy usually less. I have a new thermostat and going to install tomr, but would that cause the problems im having???

What did the plugs look like?

I know smoke machines are supposed to be pretty sweet, but did you try checking the vacuum with propane?

the old plugs were not to bad considering they were original, i have not tested vacuum, but I ordered a new Fuel pressure regulator and should be in by morning.

if that car is all original I'd plan on changing ALL fluids, including a transmission flush, brake fluid flush, coolant flush, and engine oil change (after putting a few 1000 miles on it to stir up the stuff thats sitting from its long nap). you already did the first thing I was going to suggest, replace the spark plugs, wires, cap, rotor.

the erratic idle-when-cold could be the engine coolant temp sensor (ECT) on the side of the engine under the intake manifold. it could be the fuel pump(s). if you have a bosch injection system, you probably have dual fuel pumps. there's a transfer pump in the gas tank, and a main pressure pump under the car next to the fuel filter. the engine will run kinda OK with a dead transfer pump as long as the tank is half full or better. also, the hoses connecting the 'intake sock' to the transfer pump rot or fall off, so if you're going to go into the tank, plan on replacing that too, and the sock.

all fluids changed as well as fuel filter, spark plugs, wires, cap, rotor. Both fuel pumps working, but have not checked the hoses at the transfer pump.

Ill have to check to see if the O2 sensor is working properly also.

Also since I cleared my original codes nothing has returned in the last 80km or so, yet I still have the issues from my original post...I really hope the fuel pressure regulator works out

if its a LH2.4 car, any failures of the O2 should be reflected by OBD codes, although many might not show up until after some significant driving, although I'd expect 80km to be enough.

the engine coolant sensor, in particular is suspect any time the engine behavior is temperature dependent (like poor idle when cold). its a dual temperature dependent resistor, higher resistance when cold, lower when hot. one output is wired to the ECU (fuel injection) and the other to the ICU (Ignition). There's three sensors in a row on the engine under the intake manifolds, one is the anti-knock sensor, one is this ECT, and the 3rd is a single wire temp sensor that goes to the dashboard temp gauge.

LH2.4 cars don't have a cold start injector, they just enrich the mixture when cold via the main injectors under ECU control.

oh, another 240 specific thing... the awful flap in the bottom of the air filter box, which is supposed to let warm air into the airbox from a riser over the exhaust manifold when the outside temp is very cold. I highly recommend wiring that flap closed as that thermostat controlled flap often jams open, then when its warm out, the hot air overheats the AMM/MAF causing its premature failure. When working properly, this flap should only open if its sub-0c outside.

OK, so I changed the injectors and the car still had the same symptoms as before, and code 1-1-3 came up again, could this be O2 sensor? I have a code explanation sheet and it says 1-1-3 is injectors or Lambda switch in 94 and up vehicles, could it be O2 issue for a 1993????

this table, Engine and OBD Diagnostic Codes says, fuel trim too rich or lean, and suggests one cause is the wiring to the o2 sensor.

another cause of too rich is excess fuel pressure, which can be caused by the vacuum line to the back of the fuel pressure regulator leaking. air leaks in the intake ducting or exhaust manifold can cause excess lean readings.

O2 tested fine, tested TPS, and cant find any leaks. I did run the car with the TPS unplugged and didnt really notice a difference..maybe I tested it wrong??

Should there be a difference when the TPS is unplugged??

all the TPS does is tell the ECU that the engine is at idle, so it enables the idle control valve to maintain a steady idle. if everything else is working OK, then it would probably idle, maybe a little slow, without the ICV. or, if the throttle plate is sticking a bit open, it might be idling a little too high without any assistance from the ICV (Idle should be right aruond 600-700rpm)

idle is fine when able to stay running, it seems after its able to stay running its fine(other then power surges and near full throttle) im lost at where to look now! haha

Crank Position Sensor?? any idea of location and how to test it?

the CPS is behind the engine block, right where it joins the transmission, and reads notches on the flywheel/flexplate. if its bad, your engine doesn't run at all. the wiring is more frequently a problem rather than the actual sensor, which is a simple magnetic coil. intermittent wiring issues can cause stalls, also heat soak issues (hot engine won't start but starts when it cools down). no CPS == no fuel AND no spark.

what happens near full throttle? does the engine stutter like its losing power? thats indicative of a clogged fuel filter and/or weak fuel pump and/or funky fuel pressure regulator. or a weak coil. or bad spark plug wiring.