loooong start. 1990

at first i thought that it was a sensor. but when i sprayed throttle body cleaner in it it started right up. surprising because on my other car it took forever to start because of the throttle body cleaner.

and i thought it was low fuel pressure so i cycled the key on and off but that didn't help.

ive got all new injectors and fpr so im confused. and its a 1990 4.0L

How long is loooong?
Renix engines usually take a little while. My 90 has always done this, even after a motor swap.
I like it because it allows it to build some oil pressure before it fires.

well thats true its about the normal long start. but as i said it fired right up when the tb cleaner was in it.

Well does it consistently fire up right away with the TB cleaner? or just that one time?

I ask because mine has a long start to, although about 1 out of every 5 starts will fire up without the long wait.
So maybe it was just a coincidence with the cleaner? :dunno:

no it did it twice with the b cleaner. and it has never done it before.

RENIX wants valid signals from BOTH the CPS (Cranskhaft Position Sensor) and SYNC (camshaft position sensor) before it will fire the fuel injectors and the ignition - and it wants to see an estimated crankshaft speed of 300rpm. There are various reasons posited as to why - many apocryphal - but we learn to live with it.

RENIX will start without a valid SYNC signal (it will "guess" until it hits a runner, I've tried this,) but the condition is quite obvious. RENIX will NOT start without a valid CPS signal - and if your CPS is on the way out - or has a shonky connection - that could delay starts.

The engine will start right up with Tbody cleaner for much the same reason it will with ether - it's easier to light than gasoline vapour, and probably ignites upon compression. Once that gets started, and the ECU starts firing fuel injectors, it becomes self-sustaining.

Also, failing/corroded/dirty mains can cause slow crank (delaying starts,) and a dirty/corroded/failing ground strap from the cylinder head to the firewall WILL cause trouble (it's called a "RENIX Killer" for a reason!)

Also, a failing/dirty TPS (yours is probably getting old...) will cause trouble with starting. It usually won't prevent starting, but make starting more difficult and cause idling trouble.

Check, in no particular order:
CPS connection (3-pole Delphi Weatherpack with two wires in - you'll see this at the back of the fuel rail. And, a good sensor should show something like 125-275 ohms at ambient temperature.)
TPS action/adjustment (better to check with analogue ohmmeter, than digital. You're looking for a clean, smooth sweep of the needle when you move the throttle)
SYNC sensor (Use analogue voltmeter set to 15VAC. Backprobe with wiring still connected - + lead to BLU wire, - lead to GRY/tracer. Crank engine, you should see about 5VAC.)
Check for vacuum leaks (just for giggles - these can cause all kinds of Hell!) at the manifold mounting surface, throttle body base, and all Nylon engine management vacuum lines. Vacuum lines can be had from NAPA for RENIX - about $50/set, and all three part numbers you'll need are posted on here somewhere...)

Report back after testing, and if you need more detailed test instructions, we can help you.

5-90

tps is brand new. the other on went up to 3 volts then started over. the cps if i can remeber was within spec.
if you can send a picture with all the sensors location. (manily the sync sensor.) and i cannot test them due to the fact that it is currently in storage.
but i will make notes to what it is i should do.

The CPS is at 1100 on the rear of the engine, screwed to the bellhousing. You should be able to see it from up top, but it's easier to access from below... (damn. AMC got something wrong there!)

The SYNC sensor is in the distributor - if you pull the cap off, you'll see the rotor. There's a sort of plate under the rotor, and the SYNC sensor is under that. Replacing it requires removing and disassembling the distributor. Access it electrically by the three-wire connector coming out of the distributor.

You already know where the TPS is, since you changed it. Bear in mind that it's set referring to a percentage of the reference voltage supplied by the ECU - so it's not an absolute. Work with the voltage signal as supplied, and divide it according to procedure (which I'm not looking at at the moment...)

You can get a set of "Weatherpack" tools from your local, which would allow you to remove the pins in a Weatherpack and clean them individually - thus doing a better job. I usually use a plan "brass toothbrush" for basic cleaning, or an old toothbrush and cheap toothpaste (NOT gel!) for deeper cleaning - remove the part and rinse with the hottest water you can stand, then reassemble...

5-90

well when i get my jeep back i will check the cps and the sync. it sounds like it has to make a complete revolution be for it will begin to fire.

More like two or three - but the engine cranks faster than you might think, when the starter, battery, and mains cables are all in good condition.

Also, try turning the key to ON and leaving it there for a couple seconds (don't turn it off!) and crank it.

Throttle body cleaner/carburettor cleaner is flammable. Not quite so much as ether (starting fluid,) but it will still burn and provide a fuel when cranking.

Apparently, as fuel pumps get older, they may take a little longer to develop spec head pressures - there may also be a check valve in there to maintain pressure for a little while, and that might be getting old as well. To support that argument, I do note that my 88 starts quicker during the day (while running errands,) than after sitting overnight...

5-90