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Efi doesnt work anymore

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399strokerEB

399strokerEB

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Engine is a stock reman 351w, sold the stroker unfortunately. Harness is a Ron Francis. Got g to try jumping the ground direct to the battery and see what that does.
 

thorgan

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Dec 26, 2012
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The 351 will suffer similar problems, just not as bad. What is the box code on the computer? - either a 3 or 4 digit code such as A9L, A9P, E9C1, MDE2, etc.

In the Ron Francis harness, does pin 46 go to a good chassis ground? I've read that Fox body harnesses have poor grounding but the harness you're running is an unknown.
 

Broncobowsher

Total hack
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Fuel pressure should be a 42.5 PSI delta across the injector. With vacuum on the intake the regulator backs off the pressure to keep the same pressure drop. So at idle mid 30's fuel pressure (refereced to ambient) is correct.
 

OX1

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Aug 26, 2003
Messages
3,458
Here is what's been replaced so far, distributor, coil, ecm, mass sensor, relays. I even swapped my old ecm into a fox body and the car ran. I'll have more time to mess with it today. Charging system is good. Thanks guys

Another one to check EEC power @ the ECM. I extended that main power wire on an
aftermarket harness in my dads fox body hotrod. After that, it would
not start hot. Went crazy over that for months (throwing all kinds
of parts at it like you). It was only a drop of about .2-.3 volts vs actual
voltage at battery. Ran larger guage wire for extension and it was fixed.
 
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399strokerEB

399strokerEB

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I think I found the problem! The power and ground wires to the mass air connector have continuity and the positive has no power.
 
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399strokerEB

399strokerEB

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Well I found it, a freaking o2 sensor shorted out. I've been on the phone with Ron Francis tech support three separate times and no body mentioned that as a possibility. I asked if they had a wiring diagram and they said to just use a factory fox body diagram, that does not have any wires going to anything that has to do with the mass air wiring. I'm a little po'd I had to tear half my harness apart to trace wires! So I guess I'll be buying new o2 sensors tomorrow.
 
Last edited:

73azbronco

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So it didnt do the magical rough idle with the piece of metal trick when you disconnected the o2 sensor, great find.
 

EFI Guy

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Glad to hear you found it! If the o2's and the MAF share the same power feed then a factory diagram would be of no use. In factory form the MAF is powered from the EEC relay.
 
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399strokerEB

399strokerEB

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Well I still have continuity between the power and ground wires to the mass air connector after replacing both o2 sensors.
 

EFI Guy

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When you say continuity, do you mean less than 2 ohms? I would expect to see whatever resistance passes through the O2 heater circuits.
 
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399strokerEB

399strokerEB

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Ok, what concerns me is because they tie the o2 to the same relay as the mass air I'm getting continuity at the power and ground of the mass air. Not sure if that's where my problem is but I don't like it.
 
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399strokerEB

399strokerEB

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Well I started doing some more digging and am disappointed in the harness assembly and hope this isn't common practice. I was testing the resistance of the main harness ground to the mass air ground. I had over 20 ohms, which seemed really high. Found a section in the harness where the ground wires connect and I peeled off the heat shrink. No broken wires but I noticed that when I messed with the connection the ohms jumped all over. The connection looked like something someone would have done as a quick trail fix to get home.
 

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ransil

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Well I started doing some more digging and am disappointed in the harness assembly and hope this isn't common practice. I was testing the resistance of the main harness ground to the mass air ground. I had over 20 ohms, which seemed really high. Found a section in the harness where the ground wires connect and I peeled off the heat shrink. No broken wires but I noticed that when I messed with the connection the ohms jumped all over. The connection looked like something someone would have done as a quick trail fix to get home.

Looks like a good splice as long as the solder penetrated all the wires.
20 ohms from what point to what point?

Pin 20-40-60 should go to these wire, there should be a main ground wire somewhere that attaches to the body ground, how it that one attached?
( sheet metal screws to the body make for shitty grounds)


I like to use these for grounds, one common point, if I have a problem I know where to go.

https://www.delcity.net/store/PowerPost-Plus-Cable-Connectors/p_807999.h_807991
sample only can be had cheaper elsewhere
 
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399strokerEB

399strokerEB

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The the 20 ohms I was getting was from the main ground of the efi harness to the mass air ground pun, and the battery terminal. The problem was that when I messed with the splice the ohms would jump all over. I may just try re-soldering it and see if that fixes it. I have a ground terminal block I found yesterday, I'll have to throw that on and probably extend a couple wires.
 
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