When you click on links to various merchants on this site and make a purchase, this can result in this site earning a commission. Affiliate programs and affiliations include, but are not limited to, the eBay Partner Network.
Stock XJ Cherokee Tech. All XJ Non-modified/stock questions go hereXJ (84-01)
All OEM related XJ specific tech. Examples, no start, general maintenance or anything that's stock.
For my 1990 4.0 liter Renix engine.....My scan tool tells me my Renix ecu is staying in open loop. This after the jeep is fully warmed up. I am getting a O2 sensor voltage display, about 2.3 to 2.9 volts at idle but it will increase to 3 or 3.5 when engine speed increased. Thus I think the O2 sensor is functional, O2 sensor is only a few thousand miles old. Both my short and long term fuel trims are stable at 128. and injector pulse width is about 5 or so when warmed at idle it was about 9 when engine cold. Coolant at 187F per the scan tool.
What will cause the ecu to not enter closed loop mode?
Coolant temp too low or sensed as too low, but that isn't it in your case as the scanner reports normal.
My cars report fueling as one of three states: "closed loop", "open loop", and "open loop drive". Closed being normal, open for warmup, and open loop drive for heavy throttle.
That being said, if yours doesn't differentiate between the two open states perhaps an out of adjustment throttle position sensor could cause it. Should be a quick check with your scanner.
Coolant temp too low or sensed as too low, but that isn't it in your case as the scanner reports normal.
My cars report fueling as one of three states: "closed loop", "open loop", and "open loop drive". Closed being normal, open for warmup, and open loop drive for heavy throttle.
That being said, if yours doesn't differentiate between the two open states perhaps an out of adjustment throttle position sensor could cause it. Should be a quick check with your scanner.
Throttle position was listed on the scan tool as "closed" , and the position reading listed as 17% which is within the specification for throttle position setting for closed.
Now I have tied two different ecus, and two different MPS My MAP voltage seems high, as the manual claims it should be 1.5 to 2.1 volts at hot idle
I also noted that at hot idle when I restart the motor, the idle can dip down to 450 rpm or so, and when it is below 500 rpm the ecu will go into closed loop mode temporarily, then the idle will surge to 1200 to 1500 after 5 to 10 seconds and at that time she goes into open loop, if she drops again to less than 500 she goes into closed loop ( or she goes into closed loop which then makes her go to below 500 rpm) this may cycle several times, then stabilize at 600 or so rpm and open loop operation, until I turn her off and then restart.
I drove on freeway while monitoring, and she stayed in open loop the entire time.
Your manifold vacuum is weak, but I believe in this case that is not a real sensor, but is calculated from the MAP sensor which you already found is off. I would check the wires for this and the vacuum line feeding it.
Your manifold vacuum is weak, but I believe in this case that is not a real sensor, but is calculated from the MAP sensor which you already found is off. I would check the wires for this and the vacuum line feeding it.
Thank You. That is very helpful. I will look for vacuum leaks.
update....well I put a vacuum gage on the intake at the fuel regulator port on the manifold, gage reads 8 inch of Hg vacuum, it matches the MAP sensor value, which means I have poor intake vacuum. Tried the carb cleaner spray on various fittings and manifold to head areas, but it was not conclusive as the idle is hunting so much anyway that I cant tell if the spray is causing idle changes. Visual inspect of vacuum hoses did not find any defects.
Will need to hunt down why vacuum is so poor.
PS... Update, the plot thickens... I got a small hand vacuum pump and tested a few accesories, The brake booster has a small leak, I cant pump mkre than about 4 inches Hg below atmosphere and it leaks back up in a few seconds, The evap charchol can also leaks back fairly quick, as does the erg exhaust solenoid (but is that not supposed to vent anyway when it does not want the egr to activate?) and the aircleaner thermo vacuum valve leaks back. so I got four items that that have leaks, but I am not for sure certain if the egr and evap can are supposed to have small leakage. Does anyone know?
so what I did was disconnect these items from the manifold and plug their ports, and tested the engine. No change, I still only get 8 inches Hg of vacuum at idle with these ports blocked.
So on these four leaky items, are any supposed to have a small leakage? sure they are not the cause of my issue, but if these are defective I still want to deal with them later
Borrowed a smoke machine. A good deal of smoke came out the tail pipe, blocked that off and then found smoke coming out the egr stem, from the where the stem goes into the intake manifold.
I expect the charcoal canister should be a leak by itself. Usually There is a vent line from the tank through the can and then through an electronic valve into the intake. That way the valve can control if/when it leaks through to the tank to extract vapor. If that solenoid valve is stuck open that might be a small problem.
The EGR would be a small problem.
I don't think the brake booster should leak through like that.
But the elephant is that you should not be able to put smoke in the intake and have it come out the exhaust on an engine that isn't turning. You could have a hung up valve or a burned valve or damaged seat. You'll want to do a leak down type compression test to locate this problem.
But the elephant is that you should not be able to put smoke in the intake and have it come out the exhaust on an engine that isn't turning. You could have a hung up valve or a burned valve or damaged seat. You'll want to do a leak down type compression test to locate this problem.
How about if the diaphragms in the EGR are destroyed?
Removed the egr.
1.. The egr vacuum diaphragm is leak tight, tested with my hand vacuum pump, holds vacuum.
2.. But the valve seat inside of the egr, well it fell out, I think it was swaged internally, it was rattling around. thus even when the valve is closed, it is actually very much open, that is my huge intake leak no doubt.
see image.... I am shining a flashlight into the egr, and you can see the light getting right past the "closed valve" becuase the seat for that valve is sitting there on the workbench. UGH! The light is a crescent of white you can thru the port.
I did a web search for a replacement valve. every place I looked says out of stock, no longer available, and Mopar says "discontinued".
So now I have to try to find a replacement. I doubt there is anyway for me to be able to re insert the valve seat and swag it, as the whole egr would need to come apart.
Anyone got an egr valve for a 1990 XJ six cylinder (the 4 cylinder egr is available) mine has the exhaust back pressure transducer tube. Is there an alternate valve that can be used, perhaps a simple one without the transducer tube? The 4 cylinder version has no transducer, but I have no clue as to if the mounting holes or ports will line up on a 6 cylinder. I will need to pass smog, and they do check egr operation, but I might be able to get away with no transducer.
Good point. An EGR failing in that way could let the smoke through. Also, thinking about it hard, it might be possible, with some camshafts, for the engine to stop at just the wrong point so that valve overlap could pass it, but usually it would stop where at least one direction is all the way closed on each cylinder. You could check for that by doing the smoke test again after rotating the engine just a bit by hand.
But for now I would go with the EGR. If no other solution comes along you could permanently block off the EGR but leave it on the vehicle connected in other ways so you get no check engine. It isn't nearly as important to exhaust content as the cat and the O2 sensor are. For starters I'd look for one at the junk yard.
Last edited by doublechaz; 02-06-2021 at 10:28 PM.
02-03-2021, 09:09 PM
Renix 1990 4.0 liter closed loop/ open loop Oxygen Sensor Operation
