Replaced Valve cover gasket, injectors and fuel filter, now misfiring randomly

[Big_Mark]

Hi All, my most recent upgrade has caused an unexpected side effect.

I decided it was time to replace the leaky valve cover gasket and single port injectors and fuel filter on my 1989 MY 4.0.

The valve cover job went well (aside from having to extract 2 bolts from the head  ) and the injector job was fairly easy with the exception of waiting for Jegs to send me new fuel line quick disconnects. Fuel filter replacement was uneventful aside from replacing the short lengths of hose and clamps.

After I got all the stuff back together and buttoned up I went for a test drive which for me is a quick hammer down through our lower acreage in 4 low, 2nd, 3rd,4th as fast as I can go in a short distance, then back in 2wd for a street drive on pavement 1/2 mile that includes a 200' elevation gain straight up a hill to a State Park. All went well and the engine was running really smooth at the park so I decided to go further and head into town (Snohomish WA) on a flat paved back highway. As I went down hill under compression I noticed a little bit of stumbling but nothing major. When I got to the "T" at the highway I put it in 1st to drive off when I felt the first stumble, it either feels like no spark or no gas, not sure which it is. So I compensated by taking out out of gear, wap, wap wap on the throttle until it was running normal then I slipped the clutch until I got the Jeep running down the road. At this point the little "house" or "Up arrow" light came on on my left bank of indicator lights. I do not know what that is an indicator of however every time it comes on the engine runs like this. It comes on and off as the issue arises and goes away. I was eventually able to hobble the MJ home and start troubleshooting and searching for others with similar issues  Found one here!

 

I read through Dammerung's journey and went on one of my own, here's what I've discovered along the way

 

1. I have not done Cruiser54s Sensor ground mod yet but I did test the TPS using Cruiser54's method, there was no fluctuation in the ground resistance, while I am not ruling out a ground issue I do not think this is the root cause of my problems at this time since the issue only came up after specific work was done on the Jeep, and it occurred after a 10-15 minute period of driving.

 

2. I removed and reinstalled the original injectors (turned out I already had 4 hole Chrysler injectors) < No change in behavior

 

3. I tested my CPS, it was only putting out .1 -.2v so I replaced it, and am getting a strong .5v. When the engine is running it runs smoother but over all < No change in behavior

 

4. I checked the resistance in plug wires, inspected wires, all are good, I have not pulled any spark plugs < Ad to my to do list

 

5. I checked the cap and rotor, the cap contact (middle contact from coil wire) was broken and the broken off part was stuck under the rotor contact which had bent over to the side a bit. Replaced cap and rotor < No change in behavior

 

6. Errata 21 week prior to this I took the Jeep to a spray and wash and hosed out the engine compartment to get the oil off the engine and hood and firewall, etc. I was careful to not directly spray the electronics but some overspray did get on everything. Maybe something got wet and took time and driving to ruin something?

 

Now I am out of ideas and am waiting to see what results Dammerung has before I shoot the parts cannon at other parts of the system.

 

If anyone has thoughts or ideas please post up I am willing to try them. P.S. besides checking the resistance to the battery from the TPS harness I am unable to properly test the TPS because of where it is mounted, I have a manual transmission and the expen$ive TPS without pigtails, so getting the multimeter probes in there is a physical impossibility. If I was to by any one new part it would be the TPS for an automatic, since they are cheaper and make that test (and adjustment) easier. However it seems like that isn't the issue for others so I'd rather not spend money that will likely not resolve my issue..

[eaglescout526]

Not sure what your issue is but that “up arrow” is your shift light indicator. It’s a fuel economy option for Renix engines with manual transmissions. It just let you know when RPMs are high enough for you to shift while keeping fuel economy in mind. The fact it comes on when it’s running rough either means the there’s something weird going on or your driving and the sensor in the transmission wants you to shift down until at a better fuel economy speed. The sensor is located on the passenger side of the trans. So if it comes on while in neutral you either have the REM plugged in or it’s shorting out. 

[Strokermjcomanche]

Check fuel pressure , are the injector plugs in the proper places ? 

[Big_Mark]

4 minutes ago, eaglescout526 said:

Not sure what your issue is but that “up arrow” is your shift light indicator. It’s a fuel economy option for Renix engines with manual transmissions. It just let you know when RPMs are high enough for you to shift while keeping fuel economy in mind. The fact it comes on when it’s running rough either means the there’s something weird going on or your driving and the sensor in the transmission wants you to shift down until at a better fuel economy speed. The sensor is located on the passenger side of the trans. So if it comes on while in neutral you either have the REM plugged in or it’s shorting out. 

What is REM? The light doesn't seem to come on in Neutral, I can make the engine backfire if I wrap it at the throttle body about 1/4 of the time and never see the light under that test condition.

4 minutes ago, Strokermjcomanche said:

Check fuel pressure , are the injector plugs in the proper places ? 

Injector wires are plugged into the correct injectors. How can I test the injector harness? I was thinking the wires may have cracks and would like to test them all.

Fuel comes out of the rail when I press the Schrader valve, I just installed a new fuel pump this Summer.

[Strokermjcomanche]

 That is not a proper test for fuel pressure, just because it comes out of the Schrader valve doesn't mean you have adequate pressure. You can rent a pressure tester from AutoZone if you don't have one or any other big box stores. There are a lot of junk Brands for fuel pumps so it can be bad already , and that doesn't mean that the rubber hose hasn't slipped off or leaked like it has for many people in the past. You can use noid lights to check and make Sure the injector wires are pulsing correctly, also something you can rent.

[Strokermjcomanche]

 Also, I would check the map hose to make sure that is not cracked and plugged in correctly.

[eaglescout526]

REM is the Renix Engine Monitor made by nickintime. Highly recommend you get one and yourself a AMC MPI manual. Ok that light is operating as it should then. 

[Big_Mark]

Thanks guys, 

 

I just found this in the archives here https://www.pirate4x4.com/d1/tech/billavista/PDFs/Jeep_Renix_Fuel_Injection_manual.pdf will give it a read and continue troubleshooting per the doc. 

[cruiser54]

do the Tips.....  1,3,4, and 5 for starters. 

Make sure the vacuum line from throttle body to MAP is good.

 

Snug up your intake manifold bolts. 

[Tex06]

If you're still stumped after following all of the above, shoot me a PM. I had a similiar-ish issue (With my H.O. motor) that came from removing the valve cover....I busted a solder in my wiring harness when I moved it and it caused intermittent issues just like this. I wouldn't suspect this though unless all your grounds, vacuum lines, etc. are known good. 

 

I have a post about it....somewhere......

[Big_Mark]

On 11/21/2020 at 10:51 AM, Strokermjcomanche said:

 That is not a proper test for fuel pressure, just because it comes out of the Schrader valve doesn't mean you have adequate pressure. You can rent a pressure tester from AutoZone if you don't have one or any other big box stores. There are a lot of junk Brands for fuel pumps so it can be bad already , and that doesn't mean that the rubber hose hasn't slipped off or leaked like it has for many people in the past. You can use noid lights to check and make Sure the injector wires are pulsing correctly, also something you can rent.

This seemed to be the issue. After a FRIGGIN YEAR I finally gave up and called my buddy who is an actual mechanic. He brought a scanner and checked what he could (all my sensors are good) and we determined with a proper fuel pressure gauge that I was only getting 5 -10 psi (maybe) at the rail. So today I pulled the "new" pump and fuel gauge assembly only to find the hose had indeed partially slipped off the feeder line.

I am going to replace the pump and strap it onto the assembly, then change my tank since mine is rusty inside I'd like to have this done once and for all.

More to follow when it's back together! Hopefully in the next few weeks, not YEARS!!!!

[JMO413]

Good to hear you found the gremlin. Mine did the exact same thing.

[Big_Mark]

I finally got it all buttoned up after I had a successful start up I took a hard drive (more like hammer down light) around the yard for good measure!

 

Gas tank skid is back on, Hood and assembly is back in place and works better than before.

I had to troubleshoot my headlights, a fuse in the headlight relay had corroded, brushed it off put it back, now the lights work great again.

 

Some notes on things I had to discover along the way as it relates to Gas Tank removal and replacement.

 

1. Unbolt the emergency brake cable assembly under the truck bed and leave it off until you have replaced the gas tank and skid plate.

 

2. After you've removed all the fuel supply lines from the tank and unscrewed the gas cap assembly from the bed panel (remove the cap when pulling the tank out), and the straps are removed from the truck, you can remove the gas tank and filler hoses as one assembly. This makes removing and installing the filler hoses and tank MUCH easier.

 

3. Keep track of which tank strap is front and rear, it makes reinstalling them easier.  

 

4. Clean the threads on the tank straps, run the bolt out (to loosen it) about 1/2" - 1" on a vise, with PB Blast. The new tank will need some extra thread to get it back in there.

 

O.k. on to bigger better and more fun things!  rear shocks, motor mounts, lengthen drive shaft and beyond.....