AnotherOldJeepGuy Posted May 29 Author Share Posted May 29 I made the "plug" below. The bolt is in very tight to start then snugged further with 2 tie wraps. I don't know that this was a 100% plug but it should be very close to it. (I can redo it with come E6000 glue if it doesn't look like it is OK as is). With this one the vacuum port (but before reading your post about resetting by disconnecting the battery) I saw no change. Sluggish response to throttle, running choppy, and at least once when I got the RPMs up and let go I got a small backfire (similar to the one I posted a video of a page back). I'll go disconnected the battery and repeat the test. Link to comment Share on other sites More sharing options...
AnotherOldJeepGuy Posted May 29 Author Share Posted May 29 The battery reset didn't change the outcome, still sluggish response to throttle and running very choppy. My son has a thing called a soap cannon he uses to was his car. I'm gonna see if he will bring in over and let me use it to suds up the exhaust real good and see if any bubbles show up. Think I'll need to do that first thing in the morning when it's as cool as it gonna get since the exhaust is gonna dry out pretty fast once the motor is running, but just maybe I'll see something useful. Link to comment Share on other sites More sharing options...
AnotherOldJeepGuy Posted May 29 Author Share Posted May 29 Heading out to get the tools for checking the fuel pressure..... Link to comment Share on other sites More sharing options...
AnotherOldJeepGuy Posted May 29 Author Share Posted May 29 Got the tool from Harbor Freight and measured the pressure at the fuel rail. FPR hose attached = 30PSI FPR hose not attached = 37PSI Link to comment Share on other sites More sharing options...
Gojira94 Posted May 30 Share Posted May 30 Fuel pressure is fine, not an issue. A piece of hose and a bolt is a time-honored method of plugging a vacuum port lol. I'd say leave that in place for now while troubleshooting continues. There are plenty of places for vacuum lines to crack near the vacuum tank and the check valves may not be healthy enough to hold vacuum. Once the issue is solved, you'll want to investigate and patch up any other other vacuum line breaks, and see if the vacuum tank still holds. Maybe even get cruise control back... Meantime, I think you're on the right track to try to confirm a cracked exhaust manifold. And the O2 sensor may be dead or contributing to the issue if it's commanding more fuel if it's seeing what it thinks is a lean condition from cracked manifold. When you turn the key on prior to engine start, do you see the 'Check Engine' lamp light up during the lamp check? I wonder if the bulb might be burned out and would otherwise be illuminated. I'm willing to loan you my REM, I don't have any immediate need for it. PM me with info and I'll mail it to you. I'm still concerned about verifying spark/ spark timing. More so with the distributor indexing than anything else. The coil and module are working, at least. The coil can be tested for primary and secondary resistance easily enough with a meter while the module would require a DRB II. Link to comment Share on other sites More sharing options...
Ωhm Posted May 30 Share Posted May 30 2 hours ago, Gojira94 said: I'm still concerned about verifying spark/ spark timing. More so with the distributor indexing than anything else Poor spark can cause plugs to run RICH. Link to comment Share on other sites More sharing options...
Gojira94 Posted May 30 Share Posted May 30 One more thing - pull the distributor cap if you haven't yet. Leave the wires on it, and have a look at the rotor and the cap contacts. And try to rotate the rotor by hand. It should have a really tiny bit of wiggle to it but not a lot. Link to comment Share on other sites More sharing options...
AnotherOldJeepGuy Posted May 31 Author Share Posted May 31 21 hours ago, Gojira94 said: When you turn the key on prior to engine start, do you see the 'Check Engine' lamp light up during the lamp check? AFAIK I don't have a Check Engine lamp, I've never seen one in over the last 36 years that I can recall (which in most cases would be a good thing ). I looked in my manual and it doesn't identify one existing at least not in the instrument cluster. The closest thing seems to be the Engine Maint light that apparently went on at 82,500 miles, that was way too long ago for me to remember it, but I assume it did. 21 hours ago, Gojira94 said: O2 sensor may be dead or contributing I replaced this sensor back in Feb 2025 when I had an idle issue. The issue turned out to be very dirty TB and IAC and was completely resolved after cleaning them and putting in a new TB gasket. Of course it could still be contributing, just not because of age. 16 hours ago, Gojira94 said: One more thing - pull the distributor cap if you haven't yet. Leave the wires on it, and have a look at the rotor and the cap contacts. And try to rotate the rotor by hand. It should have a really tiny bit of wiggle to it but not a lot I'll give that a shot! Have not coordinated with my son on the soap cannon yet for the bubble test but hopefully can get that done pretty soon. 19 hours ago, Ωhm said: Poor spark can cause plugs to run RICH I'm guessing I would need another tool I don't have to test this.... correct? Thanks for all the assistance so far! Link to comment Share on other sites More sharing options...
Ωhm Posted May 31 Share Posted May 31 7 minutes ago, AnotherOldJeepGuy said: I'm guessing I would need another tool I don't have to test this.... correct? Secondary Ignition (High Tension) consists of coil wire, spark plug wires, distributor cap and rotor. All items are maintenance items. If good, check Cruiser54 tip #13 Renix Distributor indexing, as mentioned above. https://comancheclub.com/topic/73472-13-–-renix-distributor-indexing/#comment-788499 Link to comment Share on other sites More sharing options...
Gojira94 Posted May 31 Share Posted May 31 18 minutes ago, AnotherOldJeepGuy said: I'm guessing I would need another tool I don't have to test this.... correct? In general, no. We're having you go through and check things to work backward to the cause. At a high level, running rich on an EFI system has 3 causes: 1) too much fuel pressure or faulty injectors leaking/ delivering more fuel than designed/ intended 2) extra air getting in somewhere that's not accounted for by the computer - the O2 sensor then sees a lean condition and the computer commands more fuel to compensate 3) Inadequate spark to burn the fuel delivered Link to comment Share on other sites More sharing options...
AnotherOldJeepGuy Posted May 31 Author Share Posted May 31 Gotcha, I was assuming I would need some kind of tool to check for "inadequate" spark. Link to comment Share on other sites More sharing options...
AnotherOldJeepGuy Posted May 31 Author Share Posted May 31 Vacuum plug back in place and hose tied off so it doesn't wander... Pulled Dist Cap, the rotor only wiggled back and forth a tiny bit, maybe 1-2 degrees each way, very small. Things looked pretty much the same shape as when installed in Jan. Not pristine, but pretty clean. Still no soap test, but I did give the manifold to exhaust donut the slight poke test. It's not in very good shape, I am pretty sure if I upped the poke pressure I could cause it to crumble. Maybe not 100% but for sure a notable amount. Perhaps it would be worth just replacing it to rule that out? I figure if I end up working on the exhaust manifold I'd be replacing that anyway. I'd thing the cost is minimal for a new gasket. Assuming the rusty bolts will let loose, I am wondering if the donut can be replaced without removing much else? The pipe wanders around from there to the CAT, and I don't see any anchors, and I see maybe an inch of space between the pipe and the frame, would that be enough slack? It's worth confessing that I have been reluctant to crawl around under the truck while leaving it running with no other human in the cab to cut the engine and hold the brakes. But I have stuck my head under a little to try and locate from where the loud comes from but difficult to pinpoint. Link to comment Share on other sites More sharing options...
llhat Posted May 31 Share Posted May 31 2 hours ago, AnotherOldJeepGuy said: On 5/30/2026 at 12:37 PM, Gojira94 said: O2 sensor may be dead or contributing I replaced this sensor back in Feb 2025 when I had an idle issue. The issue turned out to be very dirty TB and IAC and was completely resolved after cleaning them and putting in a new TB gasket. Of course it could still be contributing, just not because of age. age may not be a factor on the O2 sensor... many reported DOA Link to comment Share on other sites More sharing options...
AnotherOldJeepGuy Posted May 31 Author Share Posted May 31 3 minutes ago, llhat said: age may not be a factor on the O2 sensor... many reported DOA Understood. Good to know. This one has been working from Feb 2025 though. But I wish I still had to old one to swap back in, since the issue back then didn't turn out to be the sensor, just to rule out it has not failed. Link to comment Share on other sites More sharing options...
Gojira94 Posted Tuesday at 11:41 AM Share Posted Tuesday at 11:41 AM I'll be back in town today and I'll get the REM on the way to you. I had another 'coulda had a V8' moment. Your CTS on the driver's side of the block needs to be checked. If it's electrically open/ failed the ECU would think it's -40F all the time and would create the super fat rich condition. If you have a meter set it for k-ohms, unplug the sensor and check it. If it reads between 1.8k ohms (1,800 ohms) and 3.4k ohms (3,400 ohms) cold it's ok. If it's OL/ infinite it's bad. Anywhere above 4,000 ohms it's junk if it's hotter than 55*F outside/ cold motor. -40*F would be 100,700-ish ohms FWIW. Link to comment Share on other sites More sharing options...
AnotherOldJeepGuy Posted Tuesday at 01:45 PM Author Share Posted Tuesday at 01:45 PM Did soap test #1 at the donut. Didn't see any bubbles on first test. But I can only test a little at a time since I have to catch it on my phone. Got about 2 minutes max before it was hot enough to evap the soap. https://drive.google.com/file/d/1UWBtZNOYjkVmAVcxKzix_9CgiTkAnvvP/view?usp=sharing Wasn't a 100% test, I don't think I got soap all the way around so I'll try again, after it cools off. This is the CTS correct? Looks like a single wire so I measure between the connector and chassis? Link to comment Share on other sites More sharing options...
llhat Posted Tuesday at 01:50 PM Share Posted Tuesday at 01:50 PM iirc, The CTS coolant Temperature Sensor, is a two wire, down on the side of the block on the driver's side... could be just above the engine mount. there is an active thread with images just below these threads... read to the end. BTW... that posted manual has testing procedures for mostly all of the sensors..... Link to comment Share on other sites More sharing options...
AnotherOldJeepGuy Posted Tuesday at 02:38 PM Author Share Posted Tuesday at 02:38 PM (edited) Wow, talk about redundancy! 3 Fluid Temp sensors! Overheating if it happens could for sure be a big deal so other than 3 failure opportunities, having 3 sounds fine with me! Edited Tuesday at 02:39 PM by AnotherOldJeepGuy clarification Link to comment Share on other sites More sharing options...
hgeranium Posted Tuesday at 02:57 PM Share Posted Tuesday at 02:57 PM 1 hour ago, AnotherOldJeepGuy said: Did soap test #1 at the donut. Didn't see any bubbles on first test. But I can only test a little at a time since I have to catch it on my phone. Got about 2 minutes max before it was hot enough to evap the soap. https://drive.google.com/file/d/1UWBtZNOYjkVmAVcxKzix_9CgiTkAnvvP/view?usp=sharing Wasn't a 100% test, I don't think I got soap all the way around so I'll try again, after it cools off. This is the CTS correct? Looks like a single wire so I measure between the connector and chassis? This is the CTS for the gauge on the dash specifically. It doesn't provide any information to the ECU IIRC; that's what the CTS on the block is for Link to comment Share on other sites More sharing options...
AnotherOldJeepGuy Posted Tuesday at 03:28 PM Author Share Posted Tuesday at 03:28 PM 3 hours ago, Gojira94 said: I'll be back in town today and I'll get the REM on the way to you. I had another 'coulda had a V8' moment. Your CTS on the driver's side of the block needs to be checked. If it's electrically open/ failed the ECU would think it's -40F all the time and would create the super fat rich condition. If you have a meter set it for 10k ohms, unplug the sensor and check it. If it reads between 9,000 down to 7,500 ohms cold it's ok. If it's OL/ infinite it's bad. Or crazy high, anywhere above 30,000 ohms it's junk. I measure ~2060. It's been roughly 2 hours since I had the engine on for about 4 minutes, and the exhaust feels cool, so I'm assuming that is cool enough. I don't have a 10k scale choice, all I have is ohm, k-ohm, m-ohm, so I used k-ohm setting. I remeasured on auto-scale and got the same value. So for sure not open or 30k+, but perhaps low. I guess maybe I should watch temp with the REM and see if ECU is getting reasonable values before I replace this sensor, especially since I don't know how much stuff is in the way for replacing it. I started up with sensor disconnected just to see what it did, it ran just the same at start up as with it connected. I only let it run about a minute not knowing what damage I might do. Link to comment Share on other sites More sharing options...
AnotherOldJeepGuy Posted Tuesday at 03:40 PM Author Share Posted Tuesday at 03:40 PM On 5/23/2026 at 5:57 PM, AnotherOldJeepGuy said: 1. Should I see the EGR "plunger/shaft" move in and out every time I rev up the engine or just sometimes? It moves sometimes. On 5/25/2026 at 11:40 AM, Gojira94 said: EGR operates at part-throttle conditions. Closed at idle and WOT. and that pop does sound like a backfire. Does the exhaust smell a little richer than it used to? And if you have someone do a quick rev like that for you while you stand at the tailpipe, do you hear it there? I went back through reading about the EGR because I am still curious about the EGR movement not being consistent. Reading back through I realized I didn't answer this post questions. I don't know that anything smells any different, if so it's not obvious to me. I don't have anyone handy to rev for me, but I'll see if I can get my neighbor to do it when he gets home from work. I'm still curious why my EGR moves only sometime when I rev up, and when it does move is when I get the backfire and the delay to accel, and want to stall, when neither happen when it doesn't move. Link to comment Share on other sites More sharing options...
Gojira94 Posted Tuesday at 07:09 PM Share Posted Tuesday at 07:09 PM 4 hours ago, AnotherOldJeepGuy said: I used k-ohm setting. 2060 on k-ohm would be a little over 2 million ohms (2060 x 1000 ohms). My Fluke 87 has a max of 5 digit places plus a floating decimal point to work with, not sure about yours. I'd like to be really really sure about this sensor before we move on. Post a pic of your reading? Consider this scenario... Upper peninsula of Michigan in mid-February, -38* (70* below the freezing temp of water) and you've got the best Prestone antifreeze in history. The density of air at that low a temperature has almost 50% additional more oxygen molecules per cubic meter than it does at +75* (1.647 kg/m3 at -38F vs 1.105 kg/m3 at +75F). Cold start is going to require a significant addition of fuel to get the engine started. More oxygen molecules in the air, and by extension the temperature of the engine based on measuring the coolant temp, means more fuel is required for an engine to run at all, somewhere between 10.5:1 and 16.5:1 air/fuel ratio. Coolant temp in the real world wouldn't get quite as low as the air temp, so this isn't a scientifically/ mathematically accurate scenario, but you get the idea... So you can imagine, a bad coolant temp sensor can fool the computer into thinking it's magnitudes of degrees colder than it is on a 77-93* day in Texas, and drown the engine in fuel immediately, whether on a cold start or hot restart. Link to comment Share on other sites More sharing options...
Gojira94 Posted Tuesday at 07:47 PM Share Posted Tuesday at 07:47 PM (edited) If your reading is 2060 k ohms, that's crazy low temp equivalent. If it's 2.060 k ohms (2060 ohms), that corresponds to about 90*F. So, after 4 minutes run time and a 2 hour cool-down sounds about right. Values corrected in this post and post a few back. Edited Tuesday at 07:53 PM by Gojira94 oops wrong table, correcting values. Link to comment Share on other sites More sharing options...
AnotherOldJeepGuy Posted Tuesday at 08:05 PM Author Share Posted Tuesday at 08:05 PM I just typed the ohm number even though I realize now I specified I used used the k-ohm scale. The correct statement would have been ~2.06 k-ohm. Sorry for the misleading post.... Link to comment Share on other sites More sharing options...
Gojira94 Posted Tuesday at 08:27 PM Share Posted Tuesday at 08:27 PM 21 minutes ago, AnotherOldJeepGuy said: would have been ~2.06 k-ohm Ok good, my bad. And my bad for the wrong numbers initially. Link to comment Share on other sites More sharing options...
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