JustEmptyEveryPocket Posted September 21, 2018 Share Posted September 21, 2018 Howdy all. I've been a long time lurker, first time poster here. Never needed to start my own thread before because I could always search and find an answer. Well this time, I'm stumped. I'm working on a 1987 MJ, 4.0L engine, BA10-5 transmission. I have done Cruiser's tips and tricks for Renix. All of them. The problem is a no start condition. It will crank, but never try to catch and fire. I have checked the CPS output. It is giving me .536VAC. So that is not it. In fact, I have spark according to an inline tester that I used. Issue first came up when I swapped in an external fuel pump. I got tired of putting bosch units in the tank, so I fabbed up an e2000 pump for myself. I wanted to be able to switch back to stock in the future, so I ran new wiring. I am using a relay, which triggers off the ACC pin in the fuse block. Power and ground are directly wired to the battery. Pump works fine, and is generating plenty of pressure, measured at 39psi at the schrader valve. So I have both spark, and fuel pressure, but it won't catch, despite turning over very happily. One thing that I am wondering about: The orange and black stripe wire from the original fuel pump relay was cut at some point. I believe this wire takes power back to the fuel pump in the normal set-up. The PO rigged it back together with some small gauge wire (which might explain why the in tank pumps kept burning up) and when I found this, I pulled it apart and secured the end. Now I am wondering if this wire somehow controls the injectors? Since I have fuel pressure and spark, the only thing I can think of that would keep it from firing is that the injectors aren't spitting in fuel. Does anyone know if injector power is routed from the fuel pump relay wire? Anyone have some ideas for me to check? Link to comment Share on other sites More sharing options...
Ωhm Posted September 21, 2018 Share Posted September 21, 2018 9 hours ago, JustEmptyEveryPocket said: I am using a relay, which triggers off the ACC pin in the fuse block. ACC circuit drops out (no voltage) during CRANK. Link to comment Share on other sites More sharing options...
cruiser54 Posted September 21, 2018 Share Posted September 21, 2018 See if the injectors have good ground and a voltage signal upon cranking. Link to comment Share on other sites More sharing options...
87MJTIM Posted September 21, 2018 Share Posted September 21, 2018 The Org/Blk wire from the relay feeds a ground signal to the ECU. If that wire is cut, the fuel pump relay will not send power to the FP. A PO may have made a work around that you have undone with your new FP. Link to comment Share on other sites More sharing options...
DirtyComanche Posted September 22, 2018 Share Posted September 22, 2018 11 hours ago, Ωhm said: ACC circuit drops out (no voltage) during CRANK. Yar. Wire the fuel pump in hot from the battery for testing. Also, you're likely to get sick of replacing external fuel pumps. Link to comment Share on other sites More sharing options...
JustEmptyEveryPocket Posted September 22, 2018 Author Share Posted September 22, 2018 On 9/21/2018 at 8:06 AM, Ωhm said: ACC circuit drops out (no voltage) during CRANK. Ahhh, did not realize that. I will try wiring it directly as DirtyComanche suggested. On 9/21/2018 at 8:34 AM, cruiser54 said: See if the injectors have good ground and a voltage signal upon cranking. Cruiser, I get ~2ohms resistance from the injector clip to the battery. And measured between the pins on the clip I get ~6mv of juice with key on. Cranking maintains ~6mv. I only have a digital multimeter, so is it possibly not seeing the quick on/off signal? Anyways, I am going to call that ok for now. On 9/21/2018 at 10:38 AM, 87MJTIM said: The Org/Blk wire from the relay feeds a ground signal to the ECU. If that wire is cut, the fuel pump relay will not send power to the FP. A PO may have made a work around that you have undone with your new FP. Not doubting what you are saying 87MJTIM, but when I backprobe the wires coming from the fuel pump relay I have Red- Constant 12V Solid Orange- Ground (with lots of resistance, but the only one that gives me an ohms reading at all). Solid Yellow- switched 12V that works with key on and then the Orange with Black tracer that gets 12V once the yellow switches on. Not sure how it could feed a ground signal in that case, but I am none too handy with electrical items. 17 hours ago, DirtyComanche said: Yar. Wire the fuel pump in hot from the battery for testing. Also, you're likely to get sick of replacing external fuel pumps. I understand that external fuel pumps have less longevity, but it is FAR easier to change them on the side of the road and get home again. While it is possible to do the in tank one, it takes longer and (at least for me) requires dropping the tank to get the seal to sit down properly. With a screwdriver and 30 minutes I can change the external pump for a new one with a minimum of spilled gas. For me, the trade-off makes sense. ---------------------------------------------------------------------------------------------------- UPDATE: Following the ideas above I tried a few things and finally got the truck to run again. 1st: Tried putting power directly from battery to fuel pump and cranking. No joy. 2nd: Re-attached the PO's small wire to connect the orange w/ black wire from the fuel pump relay. Left the pump on switched power from the ACC pin. No joy. 3rd: Kept Orange and black wire connected from fuel pump relay, AND put direct power to the fuel pump. Lo and behold it fires up and runs. So does anyone know of a good place to get constant power when the key is on AND when cranking? I can easily solder in a 16gauge wire for the orange and black wire connection. No sweat there. Although, I would like to know why that connection is necessary to make the truck run. 87MJTIM, could you explain the "ground for the ECU" part better to me? Remember, complete noob for electrical ideas. Second question: since I will be leaving power in the harness to the fuel tank do I need to worry about the pigtail in there with the fuel? I have read that gas is non-conductive, but I would be worried about something bridging the posts and causing a spark and *kaboom*. However unlikely it might be, I would like to eliminate any chances. So ideas on how to fix that? I could just cut the power wire close to the connector by the fuel tank.... Thank you all very much for the comments and suggestions. Link to comment Share on other sites More sharing options...
Ωhm Posted September 22, 2018 Share Posted September 22, 2018 Where did you locate the add-on relay for the external fuel pump? Does this vehicle have a fuel pump ballast resistor? Ceramic block on the left front inner fender. Two single wires (ORN). Link to comment Share on other sites More sharing options...
JustEmptyEveryPocket Posted September 23, 2018 Author Share Posted September 23, 2018 Relay is mounted on passenger side fender, right by the original fuel pump relay. I wanted a close run to battery power and ground. No fuel pump ballast resistor. Link to comment Share on other sites More sharing options...
87MJTIM Posted September 23, 2018 Share Posted September 23, 2018 Do you have the electric service manual? It's the 88 year, but the wiring for the FP is the same for 87. See page 16, The center top of the sheet is the FP relay. The yellow comes from the ignition switch and charges the control side. The Org/Blk feeds a ground to the ECU. The red comes straight from the battery and is hot all the time. When the control is charged, the relay sends power to the FP thru the ballast resistor (if yours has one). It also sends a signal back to the ECU. If the Org/Blk was cut from the relay, a PO must have bi-passed the factory wiring. Link to comment Share on other sites More sharing options...
Jeep Driver Posted September 23, 2018 Share Posted September 23, 2018 12 minutes ago, 87MJTIM said: Do you have the electric service manual? It's the 88 year, but the wiring for the FP is the same for 87. See page 16, The center top of the sheet is the FP relay. The yellow comes from the ignition switch and charges the control side. The Org/Blk feeds a ground to the ECU. The red comes straight from the battery and is hot all the time. When the control is charged, the relay sends power to the FP thru the ballast resistor (if yours has one). It also sends a signal back to the ECU. If the Org/Blk was cut from the relay, a PO must have bi-passed the factory wiring. ECU drives the relay, the relay does not drive the ECU. Link to comment Share on other sites More sharing options...
JustEmptyEveryPocket Posted September 23, 2018 Author Share Posted September 23, 2018 Thanks for the manual 97MJTIM. Looks like I get the fun job of tracing wires....yippee.... Link to comment Share on other sites More sharing options...
87MJTIM Posted September 23, 2018 Share Posted September 23, 2018 6 minutes ago, Jeep Driver said: ECU drives the relay, the relay does not drive the ECU. Correct. The ECU will trigger the ground that will complete the control charge. The relay will not power the FP until that ground is provided. My point being is that if the Org/Blk was cut then the ECU is not "directly" providing that ground. Link to comment Share on other sites More sharing options...
Ωhm Posted September 23, 2018 Share Posted September 23, 2018 19 hours ago, JustEmptyEveryPocket said: So does anyone know of a good place to get constant power when the key is on AND when cranking? Control your add-on relay (coil side) by using the ORN wire from the fuel pump relay (FPR_87). Do not cut this wire, but instead "T" into it. This will allow your add-on relay to act, function as the factory FPR. That is, the external fuel pump will prime during KEY_ON for 2-3 seconds and remain ON during CRANK, then RUN. Yes, ORN/BLK must be a complete circuit, as mentioned above. Link to comment Share on other sites More sharing options...
mica Posted September 23, 2018 Share Posted September 23, 2018 Great you got the rig running. Fuel, Spark, compression are the three generic things an engine needs to run. Nobody mentioned using noid lights or a stethoscope to see if injectors are cycling. Figured I would throw that in here for somebody searching in the future. Link to comment Share on other sites More sharing options...
AZJeff Posted September 24, 2018 Share Posted September 24, 2018 On 9/21/2018 at 5:13 PM, DirtyComanche said: Also, you're likely to get sick of replacing external fuel pumps. Although not direcly part of the OP's issue and solution, I am curious why you made this statement. Are you suggesting that there are no suitable remotely mounted pumps that can do the job and survive? Link to comment Share on other sites More sharing options...
DirtyComanche Posted September 24, 2018 Share Posted September 24, 2018 22 minutes ago, AZJeff said: Although not direcly part of the OP's issue and solution, I am curious why you made this statement. Are you suggesting that there are no suitable remotely mounted pumps that can do the job and survive? On average they do not live as long as internal pumps, although installation error likely plays a large part in this. The Ford pump that is commonly used actually works in conjunction with a first pump that is in the tank, which supplies the external pump with a healthy amount of head pressure. Going to a pump that was really meant to be installed externally and by itself may produce better results, but none of the aftermarket gasoline EFI ones seem to be very reliable. The diesel market is different because losing the pump is typically very costly, thus there has been good external pump (and lots of bad ones) available for a long time. Link to comment Share on other sites More sharing options...
JustEmptyEveryPocket Posted September 24, 2018 Author Share Posted September 24, 2018 Following Ohm's advice the truck is back up and running. Overall, I am happy with how it turned out. Thanks to everyone for the help and ideas. DirtyComanche: Besides leaving as much original as I could so it is possible to switch back to stock if I hate the external fuel pump; the reason I put in brand new wiring was to control installation error. This way I know the ground is rock solid, and the power is full and steady. I am hoping that part of the death of external fuel pumps comes from bad ground or bad power. Time will show me the error of my ways. Thanks again yall. Link to comment Share on other sites More sharing options...
AZJeff Posted September 24, 2018 Share Posted September 24, 2018 20 hours ago, DirtyComanche said: On average they do not live as long as internal pumps, although installation error likely plays a large part in this. The Ford pump that is commonly used actually works in conjunction with a first pump that is in the tank, which supplies the external pump with a healthy amount of head pressure. Going to a pump that was really meant to be installed externally and by itself may produce better results, but none of the aftermarket gasoline EFI ones seem to be very reliable. The diesel market is different because losing the pump is typically very costly, thus there has been good external pump (and lots of bad ones) available for a long time. So the main issue is that most of the pumps people have chosen are of marginal quality/longevity. I am familiar with the old Ford scheme of two pumps in series, and that may be a factor in why that Ford external pump works well when used the way Ford intended, but not in other applilcations. I am sure there is a pump out there somewhere, but I would bet to be reliable, they are probably expensive. Link to comment Share on other sites More sharing options...
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