1989 comanche mj Posted March 4, 2017 Share Posted March 4, 2017 My new to me 89 4 liter 5 speed has only 20psi, same with vac line to regulator on or off. I changed the fuel filter and blew the line out from fuel rail back, no change. I am running 12 volts direct to the fuel pump. (The pump wasn't coming on on its own. Tried jumping the resistor) It runs terrible but ran great while I was running a can of injector cleaner through at 28psi with the supply line crimped off. I found a receipt for an airtex e7006 fuel pump in the glovebox from 2011. The part number says its correct. Also, the pressure goes to zero right away when the pump shuts off. Are the renix trucks supposed to maintain pressure when off? I ohms checked the injectors, they are all the same. Link to comment Share on other sites More sharing options...
87MJTIM Posted March 4, 2017 Share Posted March 4, 2017 Have you checked/changed the fuel pressure regulator? If the engine doesn't have enough pressure and looses pressure rapidly then the regulator may be bad. Link to comment Share on other sites More sharing options...
Strokermjcomanche Posted March 4, 2017 Share Posted March 4, 2017 I'd say the fuel pump or the rubber hose inside the tank is bad. Airtex pumps are junk , I'm surprised it lasted 6 years , get yourself a Bosch 69302 pump and you'll be good . The hose may be dry rotted ( why you're losing pressure) .Before you do all that make sure the ground behind the drivers side tail light has a nice clean connection . Link to comment Share on other sites More sharing options...
cruiser54 Posted March 4, 2017 Share Posted March 4, 2017 I'd say the fuel pump or the rubber hose inside the tank is bad. Airtex pumps are junk , I'm surprised it lasted 6 years , get yourself a Bosch 69302 pump and you'll be good . The hose may be dry rotted ( why you're losing pressure) .Before you do all that make sure the ground behind the drivers side tail light has a nice clean connection . This^^^. And this: http://cruiser54.com/?p=249 Link to comment Share on other sites More sharing options...
1989 comanche mj Posted March 7, 2017 Author Share Posted March 7, 2017 It was the stupid rubber hose, had a tear in the bend. Nice $1 fix! But now I have an injector spraying everywhere. Link to comment Share on other sites More sharing options...
cruiser54 Posted March 7, 2017 Share Posted March 7, 2017 It was the stupid rubber hose, had a tear in the bend. Nice $1 fix! But now I have an injector spraying everywhere. Time to put a set of 4 holers in it. Link to comment Share on other sites More sharing options...
1989 comanche mj Posted March 8, 2017 Author Share Posted March 8, 2017 Oddly enough it had 4 hole injectors in it, ford yellow ones all seem to be different. I cleaned a stock set from a 90 xj and am waiting on the o rings and basket kit to put them in. I have done all your ground add ons and it seemed to help a good bit. My 90 comanche with 4 liter runs great. It came with an 8 gauge wire from the battery negative to the 15mm bolt on the ground strap at the back of the engine. Some mechanic must have done it in the past to it. Link to comment Share on other sites More sharing options...
Piilgrim82 Posted May 28, 2020 Share Posted May 28, 2020 Hey guys! I’m having very similar issues with my 90 Pioneer 4.0 5spd as the original post, but not quite sure how to check some of the things mentioned here before I try removing the sending unit. Bought a pressure gauge and I’m reading just below 20psi with the truck idling, and it immediately drops to zero with the truck off. If I turn the key to kick on the fuel pump right after I shut the engine off, I see pressure bounce to 1-2psi for a second then straight away back to zero. Replaced the fuel filter which also blew the o-ring on my pressure relief valve, but I replaced the o-ring. I’ll check my ground wire firt thing after work, but do I need to pick up an ammeter to know for sure if the fuel pump is the culprit vs the relief valve? If so, can someone tell me how/where to use the ammeter to check it? Thanks in advance!! Link to comment Share on other sites More sharing options...
JMO413 Posted May 28, 2020 Share Posted May 28, 2020 Have you pulled the vacuum line of the fuel pressure regulator to see if it's leaking? Link to comment Share on other sites More sharing options...
Piilgrim82 Posted May 28, 2020 Share Posted May 28, 2020 Nope didn’t think of that. Would fuel come out of the vacuum line? I’ll give it a try Link to comment Share on other sites More sharing options...
JMO413 Posted May 28, 2020 Share Posted May 28, 2020 It does if the diaphragm has a hole in it. Link to comment Share on other sites More sharing options...
Piilgrim82 Posted June 2, 2020 Share Posted June 2, 2020 Well I checked if the pressure regulator leaked with the vacuum line off and no sign of fuel leaking. Cleaned up the fuel pump ground and got a few more psi at idle 😂 Sadly don’t have the time on my hands to drop the fuel tank and investigate, so I’m haven’t by a mechanic give it a look. I’ll let you know what he finds :) Link to comment Share on other sites More sharing options...
Oizarod115 Posted June 2, 2020 Share Posted June 2, 2020 FYI you don't need to drop the fuel tank to get the sending unit out. Comes out the side of the tank. May need to pull the driveshaft though for ease of access Link to comment Share on other sites More sharing options...
Piilgrim82 Posted June 3, 2020 Share Posted June 3, 2020 Good to know! Was talking to a friend and he said that the fact that it increased a few psi by cleaning the fuel pump ground means my problem is most likely the fuel pump...which would make sense given that I didn’t change anything on the regulator. So when people talk about lifting the truck bed to change the fuel pump or cutting a hole in it, that’s only necessary on trucks where the fuel pump is mounted from the top? Link to comment Share on other sites More sharing options...
cruiser54 Posted June 3, 2020 Share Posted June 3, 2020 Needs a good dose of noggin pokin'. Go have a look!! YES. Could be that the hose inside is just rotted or loose. Link to comment Share on other sites More sharing options...
JMO413 Posted June 3, 2020 Share Posted June 3, 2020 1 hour ago, Piilgrim82 said: Good to know! Was talking to a friend and he said that the fact that it increased a few psi by cleaning the fuel pump ground means my problem is most likely the fuel pump...which would make sense given that I didn’t change anything on the regulator. So when people talk about lifting the truck bed to change the fuel pump or cutting a hole in it, that’s only necessary on trucks where the fuel pump is mounted from the top? Yes most electric fuel pumps drop in from the top. Our trucks have the fuel sender mounted in the side. It's easy to remove the fuel sender from the tank without removing anything else. The first time I did mine I pulled the driveshaft which gives you more room to work but it's definitely not needed. Side mount fuel pump beacuse they knew where would have issues later easier to service. LOL Link to comment Share on other sites More sharing options...
Piilgrim82 Posted July 22, 2020 Share Posted July 22, 2020 Hey guys! Apologies for not getting back to you sooner with the outcome, but guess what!...Same symptoms meant same problem! I decided to take a look for myself and as soon as I pulled the sending unit out the problem was evident, that same 2in piece of fuel line. Someone didn't properly fasten the hose clamp on one end so it was barely hanging in place on one end. Was like the engine was trying to suck from a straw with a crack in it! haha I had already bought a new fuel pump and lock ring but I'm thinking I might hold onto it in case if the old one is on its way out. If I can hear the fuel pump whining with the engine idling is that a sign it's in poor shape? Link to comment Share on other sites More sharing options...
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