hey guys, i have a 1990 S5 TII. it has the hot start problem and im looking for some advice cause I'm lost ha. it starts good when it is cold but after driving it till its hot. when i shut the car off and try to start it right back up it wont start. the car has a fuel pump cut switch that helps but its still a pain to start even when using the switch. when trying to start it i have to crack it and when its starting to get going i have to pump the throttle to get it started. i know you should never pump the throttle but it wont start any other way. i just did a compression test last week and i have 80 PSI + at each rotor.I've changed the temp sensor, plugs n wires, fuel filter, intake air temp sensor. any idea's???

 

Leaking injector?

 

Hi,

If you're saying you have 80 psi of peak/hold pressure (schrader valve installed) then this is the typical response of low compression.

I had the same issue with my 87 TII which was running similar pressures. Since at the time I was too lazy to rebuild it, I added a N/C relay to the injector +12v power feed. It was energized by a push-button below the dash.

I found this was far more effective than the fuel cut switch because that method still allows the injectors to inject all the remaining pressurized fuel before the A/F goes lean enough to fire with low compression.

The effect of inhibiting the injectors is immediate and doesn't further flood the engine.

A word of warning: wire the switch so that it can only be activated while cranking. Accidently interrupting the injectors while driving is a very bad thing. ;-)

Of course the real fix for this problem is to rebuild the engine.

BTW, also make sure your starter is cranking at the proper RPM when the engine is hot. This can give the same problem as low compression.

Russ

 

thanks guys for the feedback. Russ when i did the compression test i rented the tester from oriellys. first i took out the front leading and trailing plugs out and put the tester in the trailing hole (top hole), i unplugged the crank angle sensor and put the pedal to the floor and cranked for between 5 or 10 seconds. and did the same at the rear rotar and just yesterday i seen that my oil fill cap was cracked so im guessing that could change the readings?. is this the correct way to do a compression test? i got about 83 psi in both. i just thought anything over 80 psi was good. what is a rotary motor supposed to have for compression? i know its a lot lower that a piston engine. Thanks Russ. The info is great!

 

How to check compression.

Banzai Racing Compression Test

 

Hey thanks satch. i was reading that page just before you sent me the link. and i see that i did the test wrong. correct me if i read the page wrong but when testing the front rotar you remove either the top OR the bottom plug but NOT BOTH at one time to do the compression test. so only one spark plug is removed to do the test on the front housing, then replace plug and take top rear plug out for rear test? Thank you. This site is the best!

 

Correct.

 

Awesome. so if i was showing 80 PSi with front plugs out and texter in the top hole, leaving the leading hole open. doing it the right way should give me a much higher compression reading? Thank you Satch! and thank you for the ideas about unplugging soleniods on my other thread!

 

try shutting the car off via killing the fuel pump "pull the relay"

then start it, if it started well then it we can find a direction to go for trouble shooting it.

 

ok so i turned the car off using the fuel pump cut off switch and when trying to restart it i have to leave the switch off and crank it, it will crank a few times and then it will start to start and i have to flip the fuel pump back on quick. so its like its cleaning extra fuel out and when it just about start up, i flip the pump on and it fires off and then i can smell gas. What ideas you have for me? leaking injectors? as far as i know and the previous owner knows they have never been serviced.

 

New info.. if i kill the car via fuel pump cut off and leave the pump off it will start back up. it has to crank a few times but it will start up with the pump cut. so what does this mean? FPR?

 

Just based on your test results and symptoms, I would say it's one three possible problems:

1. Leaking injectors - you should remove them and pressure test them. (cheaper than a rebuild)

2. The compression is low because the seals are worn and the engine needs to be rebuilt.

3. Your starter is cranking under speed when it gets hot (worn brushes).

I've had trouble with all three of these one time or another.

Russ