JefCooks Posted December 21, 2022 Share Posted December 21, 2022 Hi everyone, ‘92 4.0L aw4 3 days ago I replaced my factory battery cables with a Big 7 from JeppCables.com. I also replaced my factory alternator with a 140(?)A alternator from a v8 ZJ. Upon initial install the truck wasn’t starting. It would crank no prob but wouldn’t run. I checked the relays, cleaned the fuel pump ground behind taillight but no go. I discovered that the ground I installed to the block was loose so I tightened it and everything worked but it was idling low and surging a little bit. This smoothed out after I left it running for a bit. I drove it the next day and had no issues then the following day (yesterday) I stopped at the bottom of my driveway to get the mail and when I took off it stalled and I couldn’t get it to start again. I primed the fuel pump a couple times with no luck, then randomly it fired up with me pumping the gas. I got it home and it was running fine. Right now the truck is my only transportation so I drove it to work today (I can defend my logic if you care) then to the parts store to get a fuel pressure test gauge. Upon leaving the store truck stalled, I primed it a few more times, it fired up and I headed home. I got to the bottom of my street and it died so now I’m stuck here waiting on the car gods to let my truck work for 5 more minutes so I can get it home because I can’t find a pattern to this. Here’s what I know so far: The fuel pump turns on when I turn the ignition Fuel rail gets pressure up to 40 something psi and keeps it for at least a minute All grounds are secure Truck only dies when not giving it gas I have a fuel pump & filter that I was going to install on Thursday but since it builds pressure fine I’m not sure that’s it anymore. It definitely FEELS like a fuel issue but could it be an ignition issue? Any help at all would be immensely appreciated. Thank you all Jef Link to comment Share on other sites More sharing options...
MiNi Beast Posted December 21, 2022 Share Posted December 21, 2022 How long does it hold fuel pressure? Fuel filter easy to swap out at anytime. But check fuel pressure regulator at the rail as well. Link to comment Share on other sites More sharing options...
JefCooks Posted December 21, 2022 Author Share Posted December 21, 2022 Holds pressure for at least a few min Link to comment Share on other sites More sharing options...
JefCooks Posted December 21, 2022 Author Share Posted December 21, 2022 Also, CEL is on and gives codes 12 (battery disconnect) & 22 (coolant temp sensor). Since I know I have fuel pressure at rail, could it be a throttle position sensor or something similar that might cut off signal to injectors? I can hear the fuel pump when I turn key (rather loud) and when it dies it doesn’t buck or sputter, it just dies. Link to comment Share on other sites More sharing options...
jdog Posted December 21, 2022 Share Posted December 21, 2022 Did it do this before the cable upgrade? If not I would be double triple checking everything that you touched. You've checked for fuel how about spark? Link to comment Share on other sites More sharing options...
JefCooks Posted December 21, 2022 Author Share Posted December 21, 2022 I was looking for the best way to check for spark. Is there a way to use my multimeter or should I just pull a plug and stick it in the block while cranking? Link to comment Share on other sites More sharing options...
Pete M Posted December 21, 2022 Share Posted December 21, 2022 I use this little guy. way less of a chance of sparking yourself Link to comment Share on other sites More sharing options...
jdog Posted December 21, 2022 Share Posted December 21, 2022 Can be bought at any parts store or harbor freight Link to comment Share on other sites More sharing options...
JefCooks Posted December 22, 2022 Author Share Posted December 22, 2022 I had already purchased a new ignition coil, rotor and cap before this happened so I decided to install them and see if that helps. I checked resistance on the Accel coil before install and everything was within spec. I also checked signal to the coil while it was out and got good signal. Once everything was in I grounded spark plug on block and cranked it. I AM getting spark so next thing is to go back and check the fuel again. I’ll update later. Link to comment Share on other sites More sharing options...
jdog Posted December 22, 2022 Share Posted December 22, 2022 but you need to check spark and fuel when the issue occurs Link to comment Share on other sites More sharing options...
Ωhm Posted December 22, 2022 Share Posted December 22, 2022 Have you looked at the spark plugs yet? If you’re running RICH, extremely RICH, could be Code22, Coolant Temp Sensor. Link to comment Share on other sites More sharing options...
JefCooks Posted December 22, 2022 Author Share Posted December 22, 2022 So I hooked fuel pressure gauge up again and cycled the fuel pump. This time it was not holding pressure. Pressure would climb to ~40 with ign on but then drop rapidly. I have a fuel pump on hand and am trying to install it but I don’t have a spacer to fit the new smaller pump to the assembly. Any tips on where to source one or a part number? Thanks everyone Link to comment Share on other sites More sharing options...
JefCooks Posted December 22, 2022 Author Share Posted December 22, 2022 Plugs are dark but not so much that I would consider it extremely rich. Link to comment Share on other sites More sharing options...
jdog Posted December 22, 2022 Share Posted December 22, 2022 plugs look fine, but the gap looks a bit big Link to comment Share on other sites More sharing options...
JefCooks Posted December 23, 2022 Author Share Posted December 23, 2022 I have new plugs & plug wires coming to go with new ignition stuff. I’ll check gap on new plugs. Still needing to find the plastic adapter to make new fuel pump fit in assembly though Link to comment Share on other sites More sharing options...
JefCooks Posted December 25, 2022 Author Share Posted December 25, 2022 So here’s when I’m at. I replaced the ignition coil, rotor, cap and spark plug wires as well as the fuel pump, strainer and fuel filter. I also replaced the coolant temp sensor because it was giving me a CEL. While working on the truck I left the throttle position sensor off and got another CEL which didn’t go away upon plugging it back in so I replaced that as well. Once that was all done, I hooked up the fuel pressure gauge, purged all the air out of the fuel system and it started right up. It idled great and felt strong when I would rev it a bit. I was elated. Today I decided to take it out in the road and try it out. I started heading out for a park uphill from my house in case anything happened and I’m glad I did. After maybe 1/2 mile of (pretty steep uphill) travel the truck started to miss and when I gave it more gas it died altogether. I put it in neutral and coasted back home, or at least pretty close. Now it won’t start again, no CEL’s. Sometimes it will start but immediately die and then won’t fire again. When it was idling well I pulled the CPS plug, it died, gave me a CEL, I plugged it back in, pulled battery cable for 15ish min to reset all codes and it fired up no problem so I don’t think it’s the CPS. Any other tips? Link to comment Share on other sites More sharing options...
jdog Posted December 25, 2022 Share Posted December 25, 2022 spark? fuel pressure? Link to comment Share on other sites More sharing options...
cruiser54 Posted December 26, 2022 Share Posted December 26, 2022 CRUISER'S MOSTLY RENIX TIPS IMPROVING THE FUEL PUMP GROUND JANUARY 3, 2016 CRUISER54 54 COMMENTS The fuel pump and fuel tank sending unit ground at a sheet metal screw up behind the spare tire on an XJ, and behind the driver’s taillamp on an MJ. Not only is a sheet metal screw a lousy way to ground things, this ground path is long and travels through some connectors that are prone to corrosion and moisture. Locate the black wire on the HARNESS side of the fuel pump/sender 3 wire connector. Remove a 6″ length of the split loom covering. Strip back about 1/2″ of insulation from the BLACK wire. Take your new ground wire, preferably at least 14 gauge and 12 to 18 inches long as needed, strip it about 3/4″, and wrap it around the exposed part of the harness plug wire.Solder the connection. Tape it up and reinstall the split loom covering. At the other end of your new ground wire, add a crimp on eyelet. Attach the eyelet under a bolt that goes directly into the chassis. Be sure to clean the attaching point til shiny and apply OxGard to the contact surfaces. Link to comment Share on other sites More sharing options...
JefCooks Posted December 26, 2022 Author Share Posted December 26, 2022 Definitely have spark still. Fuel pressure peaks at 42 with pump on, 38 with pump off but doesn’t drop. Fuel pressure with engine on is steady at 30-32 with no bouncing and fuel pressure goes up as engine stumbles and dies. The fuel pressure going up as it dies sounds to me like an injector or valve issue, am I way off base with that guess? Link to comment Share on other sites More sharing options...
Ωhm Posted December 27, 2022 Share Posted December 27, 2022 1 hour ago, JefCooks said: The fuel pressure going up as it dies sounds to me like an injector or valve issue, am I way off base with that guess? Since the Fuel Pressure Regulator (FPR) is connected to the intake manifold, as the engine stumbles and dies (loss of manifold vacuum), fuel rail pressure as read on the pressure gauge will climb. Normal. Link to comment Share on other sites More sharing options...
JefCooks Posted December 27, 2022 Author Share Posted December 27, 2022 Update: I was able to get a little help from a neighbor today and really check over the things I've been trying to do solo. While cranking the engine I sprayed some starting fluid in the intake and nothing happened. Good news, it's probably ignition related. Next, I hooked up a spark plug to wire connecting ignition coil and distributor cap, grounded it on block and had neighbor crank. Sparked like crazy, nice and blue. Put wire back on distributor cap, put cylinder 4 spark plug wire on spark plug, grounded on block and had neighbor crank. Nothing. When I checked ignition before I was grounding spark plug on block and recording it w/ my phone while I cranked because I don't have anyone around to help me. I would see some spark but it must have been very weak and that would explain why the truck will randomly run and then die, it's getting spark every so often but not consistently. I replaced the distributor cap and rotor a few days ago hoping that would fix the issue but it didn't. I even put the old distributor & rotor back on to see if the new one was bad, still no change. Now I'm assuming the new cap and rotor are both good but that leads me to think it's the camshaft position sensor not sending the power from coil to distributor. Is that what CamPS does? Still no CEL and no codes. Link to comment Share on other sites More sharing options...
jdog Posted December 27, 2022 Share Posted December 27, 2022 Coil sends spark to dist. Distributor distributes spark to cylinders, double check rotor is seated all the way, no play in dist shaft, make sure rotor is spinning when cranking Link to comment Share on other sites More sharing options...
JefCooks Posted December 27, 2022 Author Share Posted December 27, 2022 Isn’t the camshaft position sensor part of the distributor though? I was under the impression it tells the distributor when to send signal in HO engines. Link to comment Share on other sites More sharing options...
Ωhm Posted December 27, 2022 Share Posted December 27, 2022 SYNC Signal Generator, aka Cam Position Sensor, purpose is for firing the INJECTORS in sequential order. 91 & 92 are both HO's. _JEEP 1991 Sequential Fuel Injection Manual_1.pdf Link to comment Share on other sites More sharing options...
pizzaman09 Posted December 28, 2022 Share Posted December 28, 2022 How's the crank position sensor? Link to comment Share on other sites More sharing options...
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