Green XJ Jeep
NAXJA Forum User
- Location
- Spanaway Wa
It would be kind of a pain but how about unplugging the pump itself. Then it wouldnt matter what voltage is getting sent to it.
-
Welcome to the new NAXJA Forum! If your password does not work, please use "Forgot your password?" link on the log-in page. Please feel free to reach out to [email protected] if we can provide any assistance.
Engine miss above 2000 RPM
- Thread starter Ecomike
- Start date
- Location
- MilkyWay Galaxy
Seems I pulled the wrong FP relays, will try again today. Two different sets of images online show different spots for the various Renix relays. Also going to test the MAP with a vac gauge/pump, and test the vac line. I suspect something is still wrong there. No way it should run at 500 RPM at idle and at WOT with no changes between the two pushing the gas pedal to the floor. Also there is a pin on the starter relay that goes to the fuel pump I can pull.
Last edited:
- Location
- MilkyWay Galaxy
I am afraid that would lead to replacing both connectors at the fuel pump. If it ain't broke don't fix it or even touch it 
LOL.
LOL.Green XJ Jeep
NAXJA Forum User
- Location
- Spanaway Wa
I am afraid that would lead to replacing both connectors at the fuel pump. If it ain't broke don't fix it or even touch it
Bu then you would know your connectors are good.:laugh:
Runnin'OnEmpty
NAXJA Forum User
- Location
- Southeast USA
Forgive me if it's already been mentioned, but what about
the TPS/Throttle Position Sensor?
The exhaust popping could indicate a broken or very weak exhaust
valve spring, but wouldn't explain the rich mixture...?
the TPS/Throttle Position Sensor?
The exhaust popping could indicate a broken or very weak exhaust
valve spring, but wouldn't explain the rich mixture...?
- Location
- MilkyWay Galaxy
Starting to feel like my driveway is a junk yard now. hasta
I found the right fuel pump relay :twak:, pulled it, cranked it and dried her out
Bought a new (lost the old one) hand vacuum pump-gauge assy and used the MT-2500 scanner, ignition on, engine off, and checked the calibration of the new MAP sensor, and tested the vacuum line for leaks. Found and fixed more leaks (the rubber fitting on the MAP was not sealing perfectly,) but I doubt it leaked fast enough to cause my problems, leaked about 1" every 3 seconds with a static vacuum applied. The Map sensor data matched the Vac versus MAP kpa readings in the snap on manual, and I used a second vacuum gauge to test the first Vac gauge for porper calibration of the Vac gauge.
So the ECU, all the Map Sensor and ground wiring, the vacuum line all worked perfectly according the MT-2500. Only possible seal left to tests is the rubber thingy at the throttle body for vacuum signal leakage. But it is sealed well enough that I am now convinced this is not currently a MAP issue like I was thinking.
Can't get her running long enough and stable enough to get much use out of the scanners right now. I have to hold the throttle open a bit to keep her running.
Gonna try a night time spark leak check, then a spark plug spark test to see a new problem has started with spark.
Still will run, but only runs, stumbling badly at 500 rpm and does not care if the throttle is at idle (actually need to open the throttle just a little bit or she dies after 10 seconds) or at WOT, which puzzles the hell out me. Its like its getting the same amount of fuel and air at idle as it does at WOT. It runs the same, same stumble at WOT as it does at idle.
Could the throttle body throttle plate be not opening and just the shaft is moving? It feels normal when I rotate it by hand. I will need to pull the intake hose again to check that.
The exhaust does not feel blocked, (so no clear sign of busted CAT from the occasional backfires, YET). Back fires feel free to flow out the exhaust at the tail pipe.
It is either too much fuel or too little spark, or both or bad timing on the spark-fuel feed timing. The basic engine timing (timing chain etc) is good, just verified it has not jumped time. The valve train seems to be working fine with the valve cover off. No odd noises at all except the engine miss, stumble and sometimes minimal back fire out the exhaust.
The idle up to 2000 rpm was perfect till I ran a can of carb cleaner through the intake, and pulled the valve cover and soaked the valve train, lifters, valves, etc with pen lube and MMO.
Still watching the fuel pressure (its still perfect), spot checking the TPS data, CTS and IAT data with the MT-2500, the FPR for any sign of a fuel leak and so on. So far no suspects.
Spark plugs are fouling very quickly after each cleaning.
I got nothing so far,
I found the right fuel pump relay :twak:, pulled it, cranked it and dried her out
Bought a new (lost the old one) hand vacuum pump-gauge assy and used the MT-2500 scanner, ignition on, engine off, and checked the calibration of the new MAP sensor, and tested the vacuum line for leaks. Found and fixed more leaks (the rubber fitting on the MAP was not sealing perfectly,) but I doubt it leaked fast enough to cause my problems, leaked about 1" every 3 seconds with a static vacuum applied. The Map sensor data matched the Vac versus MAP kpa readings in the snap on manual, and I used a second vacuum gauge to test the first Vac gauge for porper calibration of the Vac gauge.
So the ECU, all the Map Sensor and ground wiring, the vacuum line all worked perfectly according the MT-2500. Only possible seal left to tests is the rubber thingy at the throttle body for vacuum signal leakage. But it is sealed well enough that I am now convinced this is not currently a MAP issue like I was thinking.
Can't get her running long enough and stable enough to get much use out of the scanners right now. I have to hold the throttle open a bit to keep her running.
Gonna try a night time spark leak check, then a spark plug spark test to see a new problem has started with spark.
Still will run, but only runs, stumbling badly at 500 rpm and does not care if the throttle is at idle (actually need to open the throttle just a little bit or she dies after 10 seconds) or at WOT, which puzzles the hell out me. Its like its getting the same amount of fuel and air at idle as it does at WOT. It runs the same, same stumble at WOT as it does at idle.
Could the throttle body throttle plate be not opening and just the shaft is moving? It feels normal when I rotate it by hand. I will need to pull the intake hose again to check that.
The exhaust does not feel blocked, (so no clear sign of busted CAT from the occasional backfires, YET). Back fires feel free to flow out the exhaust at the tail pipe.
It is either too much fuel or too little spark, or both or bad timing on the spark-fuel feed timing. The basic engine timing (timing chain etc) is good, just verified it has not jumped time. The valve train seems to be working fine with the valve cover off. No odd noises at all except the engine miss, stumble and sometimes minimal back fire out the exhaust.
The idle up to 2000 rpm was perfect till I ran a can of carb cleaner through the intake, and pulled the valve cover and soaked the valve train, lifters, valves, etc with pen lube and MMO.
Still watching the fuel pressure (its still perfect), spot checking the TPS data, CTS and IAT data with the MT-2500, the FPR for any sign of a fuel leak and so on. So far no suspects.
Spark plugs are fouling very quickly after each cleaning.
I got nothing so far,
cruiser54
NAXJA Forum User
- Location
- Prescott, Az
MT2500 knows nothing of the vehicle sensor's grounding. Only what it's output is.
- Location
- MilkyWay Galaxy
Top end looks and feels OK using hand wiggle tests of the rockers, visual inspection and running inspection with VC off. Nothing bent, or misaligned or obviously busted. TPS has passed all the tests. Working perfectly, tested with Snap on MT-2500 that shows what the ECU sees from the TPS, from idle to WOT.
It is running rich, fouling the plugs, question is why. O2 sensor works, and ECU-O2 sensor were compensating till it got worse.
It is running rich, fouling the plugs, question is why. O2 sensor works, and ECU-O2 sensor were compensating till it got worse.
cruiser54
NAXJA Forum User
- Location
- Prescott, Az
Test the ground between the MAP terminal and the battery neg terminal.
- Location
- MilkyWay Galaxy
I disagree. Maybe old_man can chime in on that, he is an EEng.
I disagree because the MT-2500 manual says that in the data mode I have been using, it gets its data on sensor readings in the data stream from the ECU. The MT-2500 is not according to the manual directly reading sensor data, it is reporting but the ECU sensor data readings are, that means all the sensors and ECU and sensor wiring and grounds must be working for me to get good normal sensor data from the MT-2500.
If the ground to the MAP was faulty, the ECU would not be getting anything but the 5V reference signal I think, as the ground is required to get the voltage drop for the signal return. That is why I love this MT-2500 scanner, because it confirms what the ECU is seeing (sensor wise) and doing in the data stream.
MAP Data:
4.8 Volts with Man Vac at 1kPa, 0" vac
3.9 V, Man vac 19 kPa, 6" Vac applied
3.2 V, Man Vac 31 kPa, 9" vac applied
etc till
1.4 V, Man Vac 65 kPa, 21" Vac applied
I will check the ground anyway, and this time I will wiggle the MAP sensor, wires and vac hose, which I forgot to do.
Last edited:
- Location
- MilkyWay Galaxy
Valve seat-seal problems is one thing I have not totally ruled out.
- Location
- MilkyWay Galaxy
- Location
- MilkyWay Galaxy
Manual spark test sent me on a wild goose chase, no spark at first, LOL. Then I figured out that the one man jump start method needs the ignition switch in run, LOL.
Got a solid, in bright daylight spark with a .060 gap (like you suggested) on an old plug. Color wise hard to tell as it was bright orange at the edges and blue in the middle. I do have spark and enough voltage to jump the .060 gap.
Got a solid, in bright daylight spark with a .060 gap (like you suggested) on an old plug. Color wise hard to tell as it was bright orange at the edges and blue in the middle. I do have spark and enough voltage to jump the .060 gap.
- Location
- MilkyWay Galaxy
Retested the CPS, still getting .60 Volts AC cranking.
The MAP sensor ground is good. MAP data is all on spec. As I recall Renix runs at idle OK, even with the MAP Vac line loose or busted, not connected to the throttle body.
Spark is good even with a .060 gap test gap. Tested with the primary HV wire and HV coil only, connected. Have not tested it across the dizzy yet to confirm the Cap-rotor are OK. They have passed visual inspection are not very old, maybe 3000 miles on them.
IAT sensor was soaking wet in oil film, cleaned it. It works, meets OEM specs.
Exhaust does not seem to be blocked at this time, and was obviously not blocked when the engine was running at much higher rpms, but stumbled at 3000 rpm, which suggests the problem was not a blocked exhaust at 3000 rpm, before it got worse, I doubt this a blocked exhaust.
Starting to think it is a Head-valve problem?
The MAP sensor ground is good. MAP data is all on spec. As I recall Renix runs at idle OK, even with the MAP Vac line loose or busted, not connected to the throttle body.
Spark is good even with a .060 gap test gap. Tested with the primary HV wire and HV coil only, connected. Have not tested it across the dizzy yet to confirm the Cap-rotor are OK. They have passed visual inspection are not very old, maybe 3000 miles on them.
IAT sensor was soaking wet in oil film, cleaned it. It works, meets OEM specs.
Exhaust does not seem to be blocked at this time, and was obviously not blocked when the engine was running at much higher rpms, but stumbled at 3000 rpm, which suggests the problem was not a blocked exhaust at 3000 rpm, before it got worse, I doubt this a blocked exhaust.
Starting to think it is a Head-valve problem?
Green Mesa XJ
NAXJA Forum User
- Location
- Pensacola, FL
Can you do a leak down test ? Seems about the only thing left.
Sent from my iPhone using Tapatalk
Sent from my iPhone using Tapatalk
Runnin'OnEmpty
NAXJA Forum User
- Location
- Southeast USA
This sounds like a carburator with the choke stuck closed.
I assume you did check to see that the throttle plate was
indeed opening up with the throttle linkage?
A clogged cat can cause these symptoms, but I know you've already checked that.
Maybe rig up an intake manifold gauge and see what the
actual intake vacuum is. That should give more info on
the problem...
This is a real mystery.
- Location
- MilkyWay Galaxy
Never done one, not sure what it tell me that the compression test did not already tell me (data in older posts here)? I think I have enough compressed air to do one. But what would it tell me?
- Location
- MilkyWay Galaxy
When the problem first started at 2000-3000 rpm I had very good flow at the muffler. Throttle plate worked when I ran the can of carb-gumout cleaner through the intake and throttle body(which worked at the time, after which the the problem moved to 500 rpm. The throttle plate shaft turns, and I do not think the 4.0 throttle body plate can avoid turning if the shaft is turning? I was thinking of cutting off the fuel (pull the fuel pump relay like before), and pulling the rubber intake boot and trying to run it with carb cleaner or starter fluid for fuel into the intake?? Any thoughts on that? My thought is it would eliminate the computer and injectors from the fuel running mode to see if it is a fuel problem or not, once and for all.
Intake manifold vacuum was great at 500-2000 rpm, when the miss problem was first at 2000-3000 rpm for a week, but at 3000 rpm (earlier), and now at 500 rpm, it misses so badly the vacuum has/had a hard time holding 10" of vacuum during the miss (at least the miss at 2000-3000 rpm did), I need to recheck it at 500 rpm, but since the vacuum would drop to 10" during the miss episode at 3000 rpm, or during acceleration misses, I assumed it was dropping to 10" at the 500 rpm miss. The miss is so bad it is tricky to keep it running at all. That no doubt is not helping the ECU-MAP operations!!!!
But is it bad valves, or the miss causing the poor vacuum???
Have not 100% ruled out the cat converter, but 98% sure it is not (yet) the problem.
I still need to do one last spark test of the secondary wires, and do it at night to look for any HV spark leaking, tracking somewhere. But I have not heard any yet. Wire sets only has 3-4 years and about 3000 miles on them. Cap and rotor the same. Cap and rotor looks almost new, like it would at about 4000 miles. O cleaned the Cap pins inside the cap like I always do when I inspect then with a sandpaper style nail file and with fast dry solvent and compressed air to remove any conductive dust residue.
Are these the symptoms of valve seats failing, or weak old springs???? It does 293,000 mile on the odo, and may be the original head.
Intake manifold vacuum was great at 500-2000 rpm, when the miss problem was first at 2000-3000 rpm for a week, but at 3000 rpm (earlier), and now at 500 rpm, it misses so badly the vacuum has/had a hard time holding 10" of vacuum during the miss (at least the miss at 2000-3000 rpm did), I need to recheck it at 500 rpm, but since the vacuum would drop to 10" during the miss episode at 3000 rpm, or during acceleration misses, I assumed it was dropping to 10" at the 500 rpm miss. The miss is so bad it is tricky to keep it running at all. That no doubt is not helping the ECU-MAP operations!!!!
But is it bad valves, or the miss causing the poor vacuum???
Have not 100% ruled out the cat converter, but 98% sure it is not (yet) the problem.
I still need to do one last spark test of the secondary wires, and do it at night to look for any HV spark leaking, tracking somewhere. But I have not heard any yet. Wire sets only has 3-4 years and about 3000 miles on them. Cap and rotor the same. Cap and rotor looks almost new, like it would at about 4000 miles. O cleaned the Cap pins inside the cap like I always do when I inspect then with a sandpaper style nail file and with fast dry solvent and compressed air to remove any conductive dust residue.
Are these the symptoms of valve seats failing, or weak old springs???? It does 293,000 mile on the odo, and may be the original head.
- Location
- MilkyWay Galaxy
I have not 100% ruled your CPS suggestion out yet. But I am starting to suspect one or more valves or valve springs are at their EOL? The lifters and rods, etc pasted a running visual inspection while cranking with the fuel off. And the compression tests were good.
90xj06
NAXJA Forum User
- Location
- Peabody, MA
hows the timing on it? have you ever changed the chain or removed the distributor? the only thing i can think of is its losing its crank signal. is the tach jumpy when its hesitating?
also STFT should be jumping quite a bit. LTFT wont really change until you drive it.
have you disconnected the battery during any of the diagnostics?
also STFT should be jumping quite a bit. LTFT wont really change until you drive it.
have you disconnected the battery during any of the diagnostics?
Last edited:
