86' Cherokee will not start, fuel problem

[dennis98290]

It has a four cylinder engine with a TBI carburetor.
If I pour gas into the carburetor it fires right up so it is not an ignition problem.
Initially the engine would catch and then stall but if I gave it throttle and got the RPMs up it would run fine. So it seems it has to do with the starting state. I had an auto parts store check two relays that I was told keep the engine running for a short period of time until the computer takes over, they tested okay. I put an ohmmeter on the TPS and the resistance seemed linear to the rotation. The resistance across the TBI is less than 5 ohms (1.5 ohms measured).
This is a great vehicle. I bought this Jeep from a friend (Boeing engineer) who had all the maintenance done by the book. It has over 200,000 miles on it with a 40 PSI operating pressure. Ed said that he had it in four-wheel-drive maybe once or twice. Would very much appreciate anyone's help in solving this problem.

 

[greg92jeepxj]

Hey Dennis , thank you for your post and welcome to Jeepz.com :welcome:
Ok , so your getting good pressure from the electric fuel pump and the injector is getting a signal from the ECM. It's now defined as a hard start/no start . You will have to check the idle air control motor on the throttle body to see if it is opening with key on . In open loop , the ECM will open the pintle for a fast idle to aid warm up until CTS reads , I believe 80 degrees or more so the ECM will go into closed loop. Hope you got a good O2 sensor because the computer depends on this signal to adjust fuel trim using its signal . The MAP sensor will need to be checked if the vacuum diaphragm is good and reading engine vacuum to send signal to ECM as well. Pull the iac motor out with engine cold , clean if needed but verify its position . When key in turned to ON position , there should be movement , it should retract slightly . This is to invite more air into engine so O2 sensor sees more air and increases injector dwell time for richer mixture for engine warm up .
once coolant temp sensor reads over the 80 or 90 degrees it need to tell ECM to go to closed loop operation , the IAC motor will return to normal operation to maintain correct idle. Good that yor TPS is working to illiminate that from the equation . Hey , do we know if the EGR is working right ? If stuck open , will cause over rich condition but if no back firing is noted as was not posted , probably not contributing to starting issue. But once ruining , it should be checked. Renix era engines are finicky and all the emmissions gear needs to be maintained regularly or the engine power diminishes quickly. If you believe spark is good and present from crank to run , it should have a good ignition module and pick up. Try these checks and hope that gets it for you .
Let us know what you find when you can . Best of luck and thank you for your membership !