Hello All!

Glad to be back. This is a followup on my previous problem regarding my old car. The problem came back but Ive narrowed down the symptoms.

Lets say we have 1 to 10 with 1 being cold engine and 10 being fully warmed engine based on temp gauge needle (temp guage needle is right below almost at the middle mark when fully warmed up).

When I start the car and let it idle without load from cold to full warm, it runs fine. Now when I put load on the car (switch to Drive or Reverse) while the temperature is around 6-9, the car bogs down, sputters, and most of the time stalls. Restarting it is not a problem as it starts right away most of the time (sometimes it hard to start and just keeps on chugging). The closer it is to fully warm, the more the symptoms got worse. But once its fully warmed up then the problem goes completely away (with occasional small sputters). The more gas I put on while the symptoms are taking effect, the more the car bogs down (it feels like its choking). Remember that this only happens with engine load. Also im only getting around 15-17 MPG (is this normal?).

This is really annoying because this means I have to wait till the car fully warms up (takes about 15-20 minutes from cold engine and its really cold this time of the year) before i can use the car going to work in the morning. Furthermore when I start the car in the morning I can sniff some smell of gas (only when first start in the morning).

I have this funny feeling that some gremlins have invaded my car's engine and are playing tricks on me.

If not the gremlins, could it be the Coolant Temperature Sensor? The car has not thrown any CEL at all.

Assuming ECT sensor is not working as it is, here is my very wild theory out of desperation (which I think is not correct but just listen to me rant hehe). When car starts cold RPM is high and fuel mixture is rich. When temperature is around 6-9 fuel is still rich and RPM has dropped lower but still more than 1K so its fine. When temperature is 6-9 and I put in load the RPM drops to around 800 RPM (this is normal right since the start needs to roll from low RPM so it doesnt lurch forward). Now this is where the problem starts, since the RPM is low and the fuel mixture is rich then it bogs down and sputters and stalls due to too much fuel (the gremlins must be rejoicing that moment). This also explains why symptoms get worse when depressing the accelerator as its getting more and more fuel. When the engine has fully warmed up (level 10) ECU switches to another mode and uses info from other sensors. So it adjusts to the correct fuel-to-air ratio (so its not rich anymore) and with this the car runs fine now even at low RPM on initial load.

if my theory is at the least partially correct, how do you replace the ECT sensor? The location is right below the distributor and its so damn tight in there. Tools needed? The ECT was full of oil/grease when I last checked so I cleaned the wire and connector (threw CEL when I removed it). I think the engine has overheated before because one time when the radiator fan broke down the coolant was boiling in the reservoir and overflowed so I replaced the fan and radiator (leaking) and few months later the symptoms above.

Or could the ECU have not been working properly (maybe due to rewirings done by the gremlins)?

Here are the new stuff in the car:
- radiator
- radiator cap
- radiator fans
- oxygen sensor
- thermostat
- spark plugs
- spark plug wires
- fuel filter
- air filter
- oil and oil filter
- transmission fluid
- rear tires

So back to the ECT sensor, how do I replace it? Is it really the culprit? Tools needed to reach it and remove it?

I hope you guys can educate me on this. Very long post indeed!

 

Replacing it is simply unscrewing it from the engine & screwing the new one in. Coolant will come out from the hole, so be prepared & be quick with the new one. You can probably do it without losing more than a couple ounces of fluid. Top up the fluid & bleed air out etc.

Is it really the culprit?
A shop manual will have a table of resistance (ohms) vs temperature. If you can reliably measure the temperature of the engine when it's warm-ish or hot, then you can check it with an ohm-meter. Otherwise, the proper test for the sensor is to put it into a pot of water together with a thermometer.

Also.... rule out stuff like dirty/loose/corroded wiring connections. I don't believe it relies on electrically grounding to the engine, because it's got 2 wires.

 

It was the coolant temperature sensor!!! The the hesitation/sputter/stall are now completely gone (during warm up with load)!

I bought a duralast sensor at autozone for about $21. Since I dont have advanced tools and the space at the sensor location is very unforgiving, here is what I did to replace it:

1. remove negative wire from battery terminal
2. remove the air pipe from filter to manifold
3. remove that thing beside the distributor (is that the ignition coil?) and all wire connections. use socket wrench and extension
4. remove the distributor using socket wrench since you now have better working space (make sure to remember the original position of the distributor end)
5. you will now have access to the temperature sensor, use #19 open end wrench
6. before completely unscrewing the sensor, place paper towel below the sensor
7. quickly replace the sensor and install the new one (make sure to place anti-sieze on the threads)
8. reverse the procedure above until #2
9. remove air in the cooling system by opening a bit the coolant bleed valve at the thermostat housing until no more air bubbles (that is if you lost a lot of coolant)
10. refill coolant as needed
11. reconnect negative wire
12. start the car and let it run for a while and check if symptoms are gone (mine did)

Hope this helps others too

 

All right, THANKS for coming back with the rest of the story.