Q45 Frustration...runs great warm, cold bucks and jerks

[aliciaford]

Ok, Im hoping someone can point me in the right direction. My 94 Q45 had hesitation and some idle fluctuation when climbing a hill and some poor accelleration. So, I cleaned the MAF, Throttle Body and that helped significantly. A week later, back to same old issue. So, I ran some BG44k thru it and decided to replace the MAF with a new OEM one. Car ran like a champ, so I figured problem solved. Next morning, let it warm up 3-5 minutes max and hit the road. The car bucked and jerked, acted kinda like a carb. car running out of fuel. At the stop light, I pulled in the gas station put it in park and the car's idle jumped around wildly. Turned it off, let sit 10 min then let it idle til the thermostat opened and car ran perfect. If thermostat is open, car runs great. Cold car runs horrible. What next??? 02 sensors? Cats? It has 153k. Hoping for ideas on where to do next...dealership? Thanks

[Mint Q45A]

I experienced something similar a couple of months ago - car would sudenly start bucking and almost die. It turned out to be the Fuel Filter.....
When was the last time you replaced it?

[turael]

I don't know too much about the vh45, but could it be the coolant temp sensor? These generally report to ecu so it can adjust afr to match.

I'd also look at the spark plugs, fuel pump, coilpacks. Is it blowing any smoke? Checked for vac leaks?

The fsm probably has a section in it for diagnosis. Sensor checking with multimeter etc.

[aliciaford]

New fuel pump approx 1 year ago. New fuel and air filters in December. Plugs 20k ago, the correct ones. Only other thing I can think of is that I sometimes hear a ticking noise, but intermittent. No vac leaks. My secondary TPS is bad, but shouldnt have anything to do with this. No smoke issues. No foul smells but I did have an overfueling issue and Im worried that might have caused an issue with the cats or O2 sensors. Its just weird, drove it 600 miles on the freeway last week, drove like a dream. But let her sit overnight and the problems back in the am. I will read more in FSM. Thanks.

[turael]

Pop out the sparkplugs and have a look. You will see if any particular cylinder is overfueling that way. While you're at it throw in some cheap coppers gapped at 1.1 and see what happens.

Wouldn't worry about the cats or 02 sensors at this stage. I don't know if the VH uses 02 sensor to adjust idle or anything other than cruising, but it's not likely to cause misfiring or bucking to the degree you've described.

The ticking could be injectors. Injectors could also cause overfueling, if they're dirty. Could be worthwhile to pull them out and get them cleaned and flowmatched, would be a couple hundred bucks.

FSM should have a diagnosis path to follow as well. Good luck and keep us posted

[IThaJ0kaI]

Coolant temp sensor.

If its bad, it will not sense that the motor is cold and will not compensate for it, once it warms up it will be in the correct parameters and will run normal.

[aliciaford]

Is the coolant temp sensor hard/expensive to replace?

[IThaJ0kaI]

I have no replaced one on a q45 yet, but for a 240sx they are only $16 and it only takes a 19mm socket to change it.

[turael]

Yerp looks to be a relatively minor job - take off the front plastic panels of the engine and its right there. There should be two I think? Anyway, grab a multimeter first and read the resistance (I think - or whatever the FSM tells you to do) to see if its within range or if its something else faulty.

[life602]

yeah i would try the coolin temp sensor...also try to messure the pressure on the fuel could be a fuel regulator or the fuel pump isnt pumping enough fuel seen it happen when a guy replaced an h22 prelude engine on a crx it ran ok but when he added the turbo it started acting out also try smellin aroud ur garage when u barely start the car does it smeel like its runnins really rich or if u dont smell anything...it should smell some what rich but not like it fill ur hole garage with the smell

[Mint Q45A]

Aliciaford, what was the end of this? Did you replace the coolant temp sensor? Did that take care of the problem?
If not, you may want to look into the MAF sensor. Look for my posting "MAF Repair..No more bucking", just in case.....