To test the output voltage at hot idle you need to back probe the wires at the connector when it is attached to the MAP sensor and the engine is running (210*F ECT).

 

Thank you. I'll check that sometime soon when the motor is war enough.

More information on the condition. Put a pressure gauge on fuel rail and it primed up to about 40psi. Took a couple rotations of ignition. Drops pressure slowly. Starting the jeep yielded a 32psi at idle. Removing the vacuum line on Fuel Pressure Regulator increased fuel pressure to 41psi.

Also I thought if I disconnected the injectors one by one I could see if one of them needed replacing. However, I really couldn't see a noticeable change when I disconnected any of them. Maybe slight, but not enough to confirm a diagnosis.

Checked each injector and all had 15 ohms resistance. No clue if they are clean or clogged.

If I pop the accelerator in neutral it feels like it wants to die as the RPMs drop. Slight hesitation on pushing down the accelerator.

 

I just pulled the plugs from the distributer cap while the vehicle was running. I thought I'd notice a big change, however, I really didn't. All affected idle, but, not by much.

I'm stumped.

Anyone know what the fuel pressure should be? I've read from 35-50psi. Anyone know for a fact?

 

I've been researching fuel pressures and I think I should be at 49psi +/-5psi. However, Ive also seen people say 32 psi is what the service manual calls for.

I'm going to replace the fuel filter and see what happens. It's probably time anyway. I'll replace it and re-test the pressure.

I might also re-test the compression.

Any other ideas?

 

Okay, I did a little research and came up with this chart. It appears as I don't have the 49psi injectors, but, the 39psi version. I showed 32 psi at idle when I checked my pressure, so, that's a 7psi difference (as opposed to 17psi).

Does this signal my problem? No clue on the age of the pump.

 

Bump. No one has any ideas?

 

My renix 4.0 idled rough for a long time. Sometimes it was the tube to map sensor was disconnected, (not noticed at a glance). Other time it was tps needed adjustment. Not sure if h.o. 4.0 is different far as a tps but it made a big difference with rough idle. Renix motors are also very ground sensitive. First thing I did was super clean every ground and electrical connection I could. Made a HUGE difference.

 

Been a long while since I've been on this site. Had to create new user name for some reason. Cruiser 54 mostly renix tips helped me a lot along with other great people on this site. Hope they r all still around. I know 93 motor is ho, but the tips will surely help you out. Also, lung head hd jeep sensor diagnostics (google it) testing for vac leaks in those old hoses would be something I'd check. Definitely affects idle. Holding a stick to each fuel injector with your ear on other end, if you don't hear a rapid tick, injector isn't working. I could run a scan tool on my 90, but have you tried? I bought the jeep with intention to sell for another, the more I worked on it, the more i loved it. Now I have two heap jeeps😊 good luck.

 

I haven't tried scanning. Don't have a scan tool and it's not drivable. Maybe I'll look into that tomorrow.

Do you know if my fuel pressure seems low?

Also, I know I sinned and put an autozone cps in the bell housing. Maybe that's my issue.

 

Not sure about fuel pressure. It never hurts to put a new fuel filter in. Cheap and easy. A bad filter slows the flow of gas to a noticeable point at idle. Deff. Check tps. All you need is a volt meter n some paper clips. Cruiser54 has a write up in his pink links. (mostly renix tips). Also check your egr diaghram. If the pintle moves back n forth on its own, or you pull it back and engine doesn't bog down, theirs an issue.

 

Forgot to mention check valve cover n head bolts for tightness. Mine need re tightening from time to time

 

I've checked the TPS. Appears to be fine. I've also swapped out three of them and none made a difference. I've got a pile of old parts I can use for troubleshooting.

I'll check head and valve torque. I'm replacing the filter this weekend and then I'll recheck fuel pressure. If it doesn't improve, I think I'll need a fuel pump. 32 psi is low for a system that should be 39 psi. Can anyone else confirm this?

 

When you checked the tps, you made sure it was adjusted properly with the mathematical equation and a volt meter, and not just looking for physical wear? I'm assuming you did but just making sure. Does the engine just idle real rough, or is it like a surge that one could set a timer to that makes your tach needle go up and down with?

 

Forgot to mention, I know you don't have a scan tool, but you could clear your computer codes by totally disconnecting the battery, or just the positive cable and touch it to the negative post for like 10-30 seconds. Then you could try turning the key on-off-on-off-on-off without ever turning the motor, a blinking sequence of dash lights should happen that should give I think two digits. Then look up that code online. It might work with your year.

 

Okay guys. I'm going to start from square 1 here. I'm going to clear the ecu, let it run for 5 minutes or so, then I'm going to look for codes. I don't haven't seen the check engine light yet, but, maybe there is a hidden code.

Also, I want to completely re-check my spark and rule that out completely. Then move on. Any thoughts? This thing is super frustrating. Most all the searches I've run never led to a solution. I'm trying to turn this into a helpful diagnosis thread when complete. I'll update the original post with the useful data when complete.