1975 Ljet 1.8l. The car starts and runs fine in cold weather. When it is warm, the engine cranks and cranks and will not start. Use a little starting fluid, it starts, but unless I keep my foot on the accelerator, it will stall until it warms up. Head temperature sensor???

Have to checked all the hoses that carry the vacuum ? Start with the small hoses, they crack and leakage is barely detectable. If there is a Y connecting hoses, make sure its not cracked. Then move to the AAR to Plenum hose, pull it and put a rubber stopper in the plenum ( Home Depot has these) Then move up to the hoses that go into the boot, they gotta seal real good. Lastl, check the gasket between the throttle body and the plenum. 914 rubber makes replacements now.

I installed a vacuum gauge into one of the lines that connect to the plenum. When everything is right, it reads a steady 18 at idle; when there is a vac leak it occilates.

If. none of these pan out; it could be the T! sensor connection or the sensor itself

Good luck with this...

yep, you have a vacuum leak. Could be anywhere or everywhere. You have to find it. Go to YouTube and search for a smoke machine. fresh paint can, compressed air, charcoal, cardboard and some hoses. Pump the smoke in, watch where it comes out.

Even the distributor can be a vacuum leak. Good luck.

Thanks for the help. I'll get my vacuum gauge out tomorrow along with a can of carb cleaner. But why does it start right up and run fine in cold weather and run like crap when the weather is warm???

Could be the extra air from the AAR and leak act together; but when it’s hot, it doesn’t like the extra air ?
Does the AAR work ? Easy to test.......

AAR was checked, it works. I was thinking the head temp sensor because it is related to cold weather vs warm weather.

That’s easy to test...,

Hey, I see you are from Salem, NJ. I live in South Harrison right around the corner. I was wondering if there is a 914 club in the area and if there is a reliable shop for 914s locally?

Thanks, Mike

Don't know of any 914 club in the area. I joined the local Porsche club in South Jersey a few years back. I was the only 914 and felt like a bastard child. They were more into wine tasting and dinners. Too rich for my blood. I don't know of any shops in the area as I do all of my own work. Try calling Joe Palma, Palma's auto repair, 529 Kings Hwy, in Audobon. 856 547 6522 and ask who he would recommend. He specializes in Bentleys, Lambos, Jags, and Ferrari's.

Checked out head temperature sensor and it read 2588 ohms cold. Hooked up a vacuum gauge and it held steady at 17. Sprayed carb cleaner around hoses and there was no jump in the idle. Gremlins? I may try a smoke test with a cigar and see what happens.

Tim and I did some trouble shooting one time. I have a Air/Fuel meter that really told me what the engine was doing during this test. But I un screwed the TS2 sensor (CHT for FI). Plugged the wire back in and stuck the sensor part in a cup of ice water and started the engine. The brain thought it was 32 * outside so it loaded up the engine with fuel.... A/F sensor gave us a rich A/F reading... 10-ish IIRC so we knew my sensor (914 rubber) and brain were working.

The graph below is partially from Ratwell's site. The green line is one of my old sensors that I replaced with 914 rubber's sensor. I did these tests in the kitchen with boiling water. should have used cooking oil to get hotter data points, but you get the idea.

what was the temp when you ohmed out the sensor? 70 is kinda hot for NJ this time of year. Does it fall in line with Blue and Red?

Click to view attachment

It was around 54 degrees yesterday when I checked the sensor. It was 36 this morning and it fired up no problem. Something is preventing the engine from getting enough fuel to start on a warm day.

Sounds like a vacuum leak to me, like the others already pointed out. To help aid with your diagnosis, using a air/fuel ratio gauge will help paint a better picture on how your car is running cold vs hot.

Several years ago I had a similiar problem; I had gone through everything, even the TB and Oil Filler gaskets.
It turned out the FI boot between the AFM and TB was cracked. Ended up repairing it with some rubber wetsuit repair glue.

Smoke would have found it after 5 minutes.

Or is your Cold Start Valve giving you extra gas on a cold day? I guess I mean maybe you aren't getting enough fuel from your injectors at any outside temperature and your Cold Start Valve makes things work when it is active? I suppose the same thoughts work for too much air (vacuum leak) all the time and the Cold Start Valve is giving you the extra fuel needed.

Looks like I have to buy a cheap cigar and do a smoke test.

got one like this for around $80 and it help me a lot find a leak with our few cars.

Click to view attachment

That is a good one. You can go cheaper tho.
Lowes has the can for $5 or was it $8?
I like the regulator. Mine came from harbor freight. Maybe $10 but it is adjustable... 1 to 5 psi. The Gas grill one is low, but not adjustable. need to stay low.
A couple of hose fitting for another $5
Some scrap hose
Charcoal
Cardboard scraps
And a compressor

I saw one that uses a bicycle tire pump.
So you can go even cheaper. No charcoal? Use incense.

I had a problem with a '75 L-jet 1.8 where it ran great at first and then after 20 minutes when the car warmed up it ran like crap. After replacing the cht and vacuum lines with no difference I replaced the maf (or whatever you call it) and that took care of it.

Buck

L-Jet has the AFM. They are NOLA and not cheap. Was the part you replaced over $300?