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VeiledLt

78 L28 EFI help...again? :(

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So I know everyone has L28 efi questions and I'm sorry for troubling everyone with another one but I am stumped honestly.

 

I have the EFI bible and my 78 FSM on my computer and have been pouring over them for the better part of two weeks and working on my car when I have days off, like today. Anyway, originally my car had no spark, I ended up replacing the ignition pick up sensor in the dist, the coil and the transistor ignition module. As soon as I had spark, my fuel pump stop cycling. I know this because it is quite loud and I heard it every other crank except for the crank when I got spark, now, no fuel. I have found that my fuel pump relay if fed by my EFI relay and the EFI relay is NOT cycling, it is making no audible noise whatsoever, I have however tested it based on procedures found in the FSM for energized and non energized testing and it is fine as are both fuel pump relays. Now as I understand it the EFI relay feeds the fuel pump control relay based off of a power directly from B+ and a "on" power from the ignition switch (key). My signal from my ignition switch is not making it to the relay. Power is coming from the switch and to the sub harness that runs along the firewall to the relay but not THROUGH the harness. Now I find it strange that randomly my harness would fail after being fine for so long and as soon as I get spark it fails, possible but seemingly HIGHLY unlikely.

 

As far as information goes the car is ALL stock, wiring has never been touched. So I am curious is there a fusible link I am missing? Does this signal go through the ECU then to the relay? I have measured for "start" signal at the ECU 32pin connector and gotten it but I am getting NO signal on the pin to test the fuel pump relay circuit. Did I perhaps test my relay wrong? I have a new one on order but it seems odd that a relay would fail as soon as I get spark. Anyway...

 

Sorry for the novel everyone but I just need some fresh ideas! You guys have always been a huge help and I would like to thank all of you in advance for any input you might have!

 

Spencer

 

 

Also I work at an Audi dealership so if anyone needs Audi help, let me know!

 

 

EDIT: Just jumped fuel pump wire at the air regulator and the fuel pump cycles. I am leaning towards needing a new ECU? Does the start signal from the ignition switch I referred too run through the ECU?

Edited by VeiledLt

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The ECU grounds the fuel pump relay(s) & ultimately the fuel pump, if I remember correctly. The air regulator & the fuel pump get B+ ,constantly, with the key in 'Run" or "Start" ,because of the high amperage draw of the pump & regulator, this was the only way to turn it on & off without burning up the ancient componentry in the ECU. So yes, I would suspect a bad ECU, since you got spark signal & then killed the fuel pump signal & vice versa. The are in correlation w/ one another IMO. Hope that helps.....

 

 

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The fuel pump relay signal also travels through the AFM. The fuel pump relay operation section of the EFI Bible is one of the thickest and nastiest parts to wade through, but I would suspect a problem elsewhere before a bad ECU, unless the car was struck by lightning (or some other, much more realistic electrical trauma occurred.)

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Sure, you can keep testing everything, but it sounds like you've been doing that already. From my experience working at Nissan, when you've completed the preliminary checks on sensors, circuits, relays, amplifiers, etc.; & the problem bounces around from system to system, the Nissan FSM suggests to "try another ECU". I found this humorous at first, till I tried it with the "yeah, right" attitude when new to these older EFI cars. When I had an older Z or pre-Max roll in the shop with lots of funky system symptoms, this cured it 75% of the time. With that said, don't let my experiences cancel out systematic process of elimination you have been using. But trust me, the old Datsun/ Nissan ECU's prior to ECCS, would go out all the time without "acts of God" spurring them on.

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Hey thanks for the help so far guys. Daeron as to what your talking about with the AFM I believe you are indeed correct and I wanted to see so I continuity checked the start signal to the relay wire (pin 4 at ECU) and the relay back to the ECU wire (pin 10) and had full continuity and avg. resistance readings at both and I THINK that if I were sending a signal to the relay I should be getting something on one of those wires and they are both getting zero voltage. I am currently in the process of attempting to track down an ECU for the car to try it out, any idea on a ballpark figure for whats reasonable? I was thinking $350ish for a new or $150ish for a used? Thanks again for the help guys hopefully I can get this figured out today I have to go back to work tomorrow haha.

 

Spencer

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So I got a new ECU, it was around $150 for a 3 month warranty. Plugged it in andddddddddddd nothing. Lame. Well on to the next thing. However, when I was cranking it over it got a little tired from spinning the starter motor so I hooked the battery charger up to it and put it on START so roughly 500amps to the battery. And, all of my relays cycled! So I am thinking excessive resistance on the positive side maybe between B+ and my relays? But where? I have checked all the fusible links and the wiring between the battery and those relays is.... 18 inches long....maybe? I feel like I am missing something super obvious, thanks for the help so far guys I feel like Its almost there!

 

Spencer

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Just had a conversation with one of the other techs at work and we were thinking it sounds like excessive resistance somewhere between B+ and maybe the EFI relay or the Ignition relay since it goes from there to the fuel pump relay AND the EFI relay unless I'm reading my diagram backwards? Im just curious as to what could cause that excessive resistance? Is there a fusible link I could be missing other then the 4 under the covered boxes attached to the relay cover and the 2 wire combo that clips to the other side?

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If you've got access to parts to swap in blind, please try an AFM... I cannot walk you through the procedure to test the circuit (heck, to be honest I'm not sure if I have ever done it myself) but if you can get your hands on a known good one, it is worth a shot.

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I'm not trying to swap parts blind man it just sucks.... I don't know what else to do and I feel lost as hell and it sucks... I mean it can only be the wiring or components and the wiring has checked out so far for continuity and resistance unless I have a fat voltage drop somewhere. Are there any fusible links that are covered or hard to find? and as far as components go I mean hell, I have a new ECU and the only other things on that circuit are the relays and they check out, aside from the afm which you mentioned but on the engine fuel wiring diagram in the FSM it doesn't show the AFM, I am NOT saying I dont believe or trust you Daeron lol I just don't know where/what terminals to look for and what to look for on them? Sorry for all the sweeping questions but I'm just lost guys, thanks in advance and I know I'll figure this out with your help eventually! Thanks again!

 

Spencer.

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Sorry to hear you must be in the other 25%, dude. I reread your first post & have a few questions:

 

1)When the key is in "Start" position, do you have B+ at the ECU harness power pin from the FSM schematic? Unplug to verify, do not backprobe.

 

2)When you try cranking, have you installed a "noid" light on one of the injector plugs? It should blink if the engine is turned by the starter faster than 50rpm's, even if not running.

 

3)Have you installed a spark tester on the coil wire & a plug wire to verify spark & strength (color)?

 

4)Have you installed a pressure guage on the fuel line exiting the filter to verify over 28 psi while cranking?

 

If the answers to these questions are yes after verification, you have a MECHANICAL problem. Check these out & get back to me, bud.

 

 

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So I'm not with the car right now but I have Sunday off so I'll be working on it then but I can tell you guys a few things right off the bat that I KNOW from working on it so damn much. So when the key is on I WILL CHECK to see if I have power at the ECU I think it shows pin 10 in the EFI bible Ill check the FSM to see if thats the same. The car has zero fuel pressure as the fuel pump is not cycling. Spark looks good from a visual gap to the end of the plug but I will check and see with a REAL tester haha. And using a noid light, damn thats a good idea, thank you! Aaand the wire to the alternator, well I know I have one, where is this fusible link your talking about though? And I think the alternator "L" signal as it is referred to in the FSM/EFI bible is only required to KEEP the fuel pump running not to start it but I could be wrong, is that what you were thinking Jaybee? Thanks for all the help guys I'm hopeful we'll get this figured out this weekend, thanks for the great ideas Nosebleedz, any more info you guys need just let me know! THanks again!

 

Spencer

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So I'm not with the car right now but I have Sunday off so I'll be working on it then but I can tell you guys a few things right off the bat that I KNOW from working on it so damn much. So when the key is on I WILL CHECK to see if I have power at the ECU I think it shows pin 10 in the EFI bible Ill check the FSM to see if thats the same. The car has zero fuel pressure as the fuel pump is not cycling. Spark looks good from a visual gap to the end of the plug but I will check and see with a REAL tester haha. And using a noid light, damn thats a good idea, thank you! Aaand the wire to the alternator, well I know I have one, where is this fusible link your talking about though? And I think the alternator "L" signal as it is referred to in the FSM/EFI bible is only required to KEEP the fuel pump running not to start it but I could be wrong, is that what you were thinking Jaybee? Thanks for all the help guys I'm hopeful we'll get this figured out this weekend, thanks for the great ideas Nosebleedz, any more info you guys need just let me know! THanks again!

 

Spencer

 

You might already know this and it doesn't look like you have messed with the oil pressure sender, but the 78s used an oil pressure switch to power the fuel pump after the engine is started, not the AFM switch. No oil pressure, no fuel. I think the the AFMs might still have the switch but it is not used, they last used it in 77. According to the FSMs. The diagram is on page EF-7 in the 78 FSM.

 

Also, I couldn't tell from your description if you had disconnected the starter and turned the key to Start to see if the fuel pump runs. I think that Start bypasses the oil pressure sender to allow the engine to start, then uses the oil pressure switch to keep it running on On. It's easier to hear the pump, check fuel pressure, etc. without the engine cranking.

Edited by NewZed

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So I'm back with my car and my FSM. Turns out the AFM is on the wiring diagram but your right Daeron and the 78 manual lists a testing procedure so I will be trying that. Still don't have any ideas why my relays WILL NOT cycle without the battery charger on 500amps.... anyone have any ideas on that one? Please? haha, well anyway, the fuel pump control relay also shows a fusible link between B+ and the fuel pump relay, where is this fusible link? And yes NewZed you are correct, the engine uses the alternator "L" signal and oil pressure only to continue running but NOT to start, says in the FSM its to prevent the fuel pump from pumping in the event of a crash. Anywho, I'll be working on the Z all day so if anyone has any input I'd love to hear it! Thanks in advance and Happy Easter

 

Spencer

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So, update, relays and fuel pump cycle with the battery charger on 25 amps, looking at fusible links I'm pretty sure, when the stores open tomorrow I'm going to go and get one of those fuse block replacement ones as recommended by atlanticz and try that out. So spark tested, spark is good however the noid light is showing nothing, my injectors are NOT cycling and the hot wire/power to the ECU, Pin 10 coming from the EFI relay is cold. I could be wrong but nearest I can tell that's the power wire. Now I have tested and retested my EFI relay but I suppose something could still be wrong with it. Other then those two problems though it should start. Please somebody have any idea?

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So, update, relays and fuel pump cycle with the battery charger on 25 amps, looking at fusible links I'm pretty sure, when the stores open tomorrow I'm going to go and get one of those fuse block replacement ones as recommended by atlanticz and try that out. So spark tested, spark is good however the noid light is showing nothing, my injectors are NOT cycling and the hot wire/power to the ECU, Pin 10 coming from the EFI relay is cold. I could be wrong but nearest I can tell that's the power wire. Now I have tested and retested my EFI relay but I suppose something could still be wrong with it. Other then those two problems though it should start. Please somebody have any idea?

 

The 78s have two in-line green fusible links mounted to the back of the metal housing that other fusible links are attached to the side of. Right in front of the battery. Looking down at the two fusible link housings from the passenger side, the other two EFI green fusible links should be just to your left. A large (4 or 6 gauge?) red wire comes out of the harness, splits in to the two green link wires at a snap-in connection mounted on the housing which then connects to two heavy gauge white wires that go directly to the battery positive. On my parts car, the two white wires recombine back to one white before the + terminal, but it looks like a PO may have done that. But the mounting position and wiring into the harness look original.

 

I was going to take a picture but my camera battery is dead. Let me know if you don't find them and I will send a picture later.

 

Fun, fun, fun...

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Have you visually inspected your main relay? It is one assembly, two large relays tied together into one box.

 

I am beginning to wonder if the solder on those relays might be old and funky, a la Honda Main EFI relay issues..... Are you familiar with that problem?

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So it runs! I had a friend who has been in the biz forever come help me out for a bit and we found that the grounding strap inside the ignition relay that grounds it through the case had snapped inside... and the contacts that cycle it had arced out and become weak. So, we pulled the relay apart, cleaned the contacts, I soldered in a new ground wire and ran it outside the case and BOOM, she runs. So I took her out for a little quick test drive with the dash out and... wow. It runs like hell, an my idle is climbing like nobodies business. When it starts its fine but everytime you apply throttle the idle climbs a little bit, AND its running SUPER rich. Could this be my ECU, its not new its a reman and the place I bought it from (z-specialties) said that it WILL RUN but he said it may run poorly so I have a warranty on it and I am going to take it in and I thinks thats my running rich problem but does anyone have any idea on the idle? TPS seems to be functioning normally and I have a BCDD Deleted Throttle body? Thanks for all the help so far guys, I will be posting pics up here in a bit of what happened to my relay.

 

Spencer

\

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Hmmm maybe I should test things first before I come on here acting like an idiot... Sorry, I pinched the air hose to the air regulator and my idle returns to normal which if I recall correctly means it is stuck open correct? I have another one which I am about to go swap in and tune the mix for the new ecu and hopefully voila' any help would be awesome though as to if the ECU could have affected my mix. Thanks so much guys for all the help so far to get it to this point!

 

Spencer

 

EDIT: So I swapped air regs and it helped ALOT! however my idle is still a tad high even with my timing almost all the way retarded, anyone have any idea why this could be happening now? aaaand I went to put the dash back in and broke a piece of a-pillar trim...SON OF A... thanks again

Edited by VeiledLt

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