Severe stumble, misfire and no start issues

Heyho, its me, again...

have severe stumble / misfire issues with my 89
Renix.

If im in P it Starts up every 5th or 6th try, Then it idles quiet low. If i accelerate slowly it runs great, if i acc a Bit more it „Stucks" at 1k rpm and stumbles, stutters and sometimes is misfiring, if i accelerate more it runs well again.

I cant Drive Like that obviously and it is anoying that it now starts to not start properly anymore...


What did i do?
Spark Plugs + Cables
IG Coil + Cap and rotor
Redid and added all the grounds
Big Cable Upgrade (except Alternator)
Removed and cleaned TB + new Seal
Removed and cleand IAC
Testet and set TPS
New Map
Checked harness ground
New Injectors (genuine Bosch 746)
New Fuel Regulator
New Fuel Filter
New Fuel Pump
New Valve Covergasket
Complete new Vacuum Harness Front and back

Im quiet lost. Im throwing parts at that thing that it should love and its Just disappointing.

The PO „removed" the EGR Valve by Just cutting and soldering the hose to the exhaust... I unplugged the EGR Vac line and closed it off.

I Even Removed the CC to rule that out...

What is throwing me Off completely is that After changing the injectors and the preassure regulator it got worse (Not starting at First try, but when it runs its Smoothie, yet the stumbling stays)

Im totally out of ideas and i feel stupid AF.
Any help? First one to solve it gets a beer as

How do the plugs look after being used?

Have you tried replacing the crank position sensor?

I will pull them tomorrow and have a look, didnt touch the cps yet cause i thought it would cause a no start condition and Not shitty Running in General

Can you post pics of your used firing pins aka spark plugs ?

I would also do a compression test at the same time!

jeep ride said:

Can you post pics of your used firing pins aka spark plugs ?

Click to expand...

Ill do tomorrow, its 10pm here and the jeep is outside
But they are in there for around a month, i dont expect horrible things

RCP Phx said:

I would also do a compression test at the same time!

Click to expand...

I sadly dont have anything to do a compression test at hand


PLUS:

I fixed my no start issue.
The PO messed with the butterfly screw, he literally just took a dreml to it and shortend it instead of turning it with an allen key, i adjusted it open a bit more since i adjusted it to factory spec while cleaning the tb, i guess my iac is toast, since it always died tried to start, i guess the iac is not opening, hence its not getting enough air...

One issue solved / error found

jeep ride said:

Can you post pics of your used firing pins aka spark plugs ?

Click to expand...

The first set of Plugs i just put in for the purpose of testing, they look good, they are from the po just for shits and giggles.

The second ones are brand new champions, not even 100 miles on them...

https://drive.google.com/file/d/1zHK7YZPmuBHKmRxcGiEj0eFR9CMHMxK1/view?usp=sharing
https://drive.google.com/file/d/15EnvwBpUkIv4GJMns0OrCDB3s-Z1A0JG/view?usp=sharing
https://drive.google.com/file/d/1qRKgT9NJz9DB9ZeMCLCgGKRmhbtYW_V6/view?usp=sharing

didnt help anything of course...

I would definitely do compression test and also a leak down test. Most of the auto parts stores here have free tool rentals!

RCP Phx said:

I would definitely do compression test and also a leak down test. Most of the auto parts stores here have free tool rentals!

Click to expand...

I will, i think a friend has one aswell.

Can the CPS cause issues like that?
I just meassured it like cruiser states, and i get .3-4v instead of the .5 and up it should get...

It starts after like two cranks, but it runs like shit..

Next thing, i know for a fact the iac is broken.

I don't remember what role the O2 sensor has in older XJs, but if it provides feedback for running at stoich, that is another potential culprit. However, the ECU would be throwing an ODB code, or at least it would with an OBD-II system.

Also, from what I've read, a bad CPS most commonly causes an XJ to stop running (my XJ ran perfect one night, and the next morning it wouldn't start), but I think it can cause a range of issues.

maxbraketorque said:

I don't remember what role the O2 sensor has in older XJs, but if it provides feedback for running at stoich, that is another potential culprit. However, the ECU would be throwing an ODB code, or at least it would with an OBD-II system.

Click to expand...

Renix cant really throw codes, sadly, luckily, i love that analoge feel yet sometimes id love some odb2

I ordered the IAC (for sure bad) CPS (0.3-0.4 Volts instead of the 0.5+ it should have) and an o2 + relay just because i have to pay for shipping anyway, i hope that solves it once and for all

Well, those Champions are black as they can be. You're running waaaayyy too rich.

I see you already have an O2 sensor on the way. What brand is it?

Are you getting a lot of smoke out the exhaust?

Saudade said:

Well, those Champions are black as they can be. You're running waaaayyy too rich.

I see you already have an O2 sensor on the way. What brand is it?

Are you getting a lot of smoke out the exhaust?

Click to expand...

Yep, that's what prompted me to ask about O2 sensor.

Saudade said:

Well, those Champions are black as they can be. You're running waaaayyy too rich.

I see you already have an O2 sensor on the way. What brand is it?

Are you getting a lot of smoke out the exhaust?

Click to expand...

And they barely have a hundred miles on them...
Most of it was running in idle for testing.

I ordered a BOSCH one + the Relay, aswell as an WVE IAC and CPS since Rock is the only good source i have to send to Germany.

But can it even be the O2s fault while standing still after coldstarts? The engine ran twice for 15mins max, else it was just minutes or an half an hour drive here and there... and the issue happens even after a cold start

It's possible it's remaining in "open loop" mode where the ECU ignores the O2 sensor input. A/F ration is determined by the MAP, CPS and CTS.

Once the engine reaches operating temp (determined by CTS and IAT), it goes into closed loop where the O2 sensor input is now used to calculate A/F ratio.

So, did your engine get up to temp when it ran for either time for 15 minutes?

Look again at your plugs. Now imagine that's all over your valves, combustion chamber and piston. It could be just so fouled up it won't run properly.

If you haven't already, try cleaning the plugs give it another shot.

Saudade said:

It's possible it's remaining in "open loop" mode where the ECU ignores the O2 sensor input. A/F ration is determined by the MAP, CPS and CTS.

Once the engine reaches operating temp (determined by CTS and IAT), it goes into closed loop where the O2 sensor input is now used to calculate A/F ratio.

So, did your engine get up to temp when it ran for either time for 15 minutes?

Look again at your plugs. Now imagine that's all over your valves, combustion chamber and piston. It could be just so fouled up it won't run properly.

If you haven't already, try cleaning the plugs give it another shot.

Click to expand...

I unplugged the O2 already, wich should keep it in open loop but that didnt change anything sadly.

I threw in some "used" but well in shape NGK that i had laying around, the black champions i took out were basically new, the NGKs didnt change anything about the behaviour sadly.

I didnt actually check if the engine got to temp, since i was so happy that it ran fine with the vac from the MAP unplugged that i totally forgot...

The sparks seem to me like its running way to rich, wich is weird since its running great when i unplug the vac of the map, wich should cause it to do exactly that...

Heres the timeline:

Bought it and drove it home for 250ish km, ran fine except a slight stumble at around 2000rpm on the highway.

Did a tuneup (sparks, cables, cap, rotor) all quality parts, ran like shit, tried the old stuff except the spark plugs, ran like shit.

Started throwing parts at it (new Vac hoses, TPS adjusted, cleaned bunch of things, complete ground overhaul, new batterie wires up to the whole fuel system including pump, filter, injectors and preassure regulator..)

I have a IAC (broken), CPS and O2 Sensor on its way thought

At this point, my money is on the front O2 sensor. My XJ ran totally rich and like crap when it went bad.