Car is an '88 3.4 swap, I finally got my idles issues fixed and the car was running great... for about 2 days

After that I now notice that I cannot hear the fuel pump priming when I turn the key on, I don't think I hear the relay clicking either. So following the advice of this post and Phonedawgz specific instructions: (which i've linked directly to)

https://www.fiero.nl/forum/F.../HTML/000774.html#p9

I checked and I get 12V on the orange and black wire, good! Then I tried the paperclip trick he mentioned and I hear the pump running, even better!

So I'm thinking the relay is bad, I tried the AC one next to it as I've read they are the same but still got no pump priming when I turned the key on.

So I bought a new relay.. no big deal they are cheap.

I plug it in, still nothing... I took apart and cleaned up the plug, put some new dialectric grease on it, still nothing.

So now I am stumped... I know the pump still works because when I did the paperclip trick i could hear it running. New relay, and a good connection from what I can see. What could be going on here?

One other thing, Phonedawgz again mentions in this post: https://www.fiero.nl/forum/F.../HTML/123455.html#p1 that the ecm could be the issue... however I am in fact getting the SES light on when I go to start the car, so I don't think that's the problem either....

Any ideas!?! those couple of days she was running fine were fantastic... now I think she was just teasing me.

EDIT: added year ('88)

[This message has been edited by OriginalDoug (edited 09-13-2017).]

In theory you should be able to start the car without the relay.....using just oil pressure. If you crank the starter for about 15 seconds and build up oil pressure, it should start the fuel pump if everything else is good. The ECM still may have a problem, even tho it lights up when you turn the key.

[This message has been edited by Gall757 (edited 09-13-2017).]

Yes the car does start, and I am aware of the backup circuit using the oil pressure switch. However once warmed up the car wants to stall when I drop back down to idle, and I'm thinking it could be a fuel issue. Either way I want to get the ECM, Relay part of the circuit working again.

Is there some test I can do by back probing one of the pins on the diagram you've attached?

Key on - you should get the fuel pump relay to come on for two seconds. Pull the relay and check right at the Dk. Green/White wire of the relay connector. If you have no power there, but you have a check engine light that works, the next thing to suspect would be the ECM. The 1227170 or equivalent ECM should be relatively inexpensive used. Go to the MALL section of this forum and see if you can get one cheap. You will need to swap the PROM from your ECM into the replacement ECM if the letter code is different on the two ECMs. Most likely they will be different unless you get one from an 87/88 with the same transmission.

Awesome thanks for the replies Phonedawgz, I will check the voltage on that wire tonight and see what I come up with.

Yup, ECM/PCM can be dead on 1 circuit and still work for other circuits like MIL light and even Scan tools.
Common one is injection driver circuit(s) go dead after driving then cooled over night.

If console is removed for any reason then See my Cave, ECM Heat
If ECM/PCM is moved make sure have enough air flow to cool it. The case is or part of heat sinking attach to driver circuits. (Same for most aftermarket sound amps and ignition boxes.)

------------------
Dr. Ian Malcolm: Yeah, but your scientists were so preoccupied with whether or not they could, they didn't stop to think if they should.
(Jurassic Park)

The Ogre's Fiero Cave

Ok so I backprobed the dk green/white wire and I get .5v at key on and it stays that way after 2 seconds, while running... all the time. Does that make any sense? what could that mean.

One other thing I discovered is that my ECM 'serv. no.' doesn't match the one Phonedawgz mentioned in his first comment. It say's 1226869. Now I know the car is a bit of a Frankenstein but it was supposed to have been built up to be an '88 GT + 3.4 swap.. tranny is 5-speed getrag... The ECM also has 3.4 swap written on it in marker, I don't know much about the computers but maybe someone attempted to reprogram it for this car??

I'm thinking maybe this could be the cause of more problems than one?

Me too.....That computer is for an '85 Fiero...depends on what PROM you have.

[This message has been edited by Gall757 (edited 09-14-2017).]

The 1226869 is the ECM for an 85. It wires up identical to and can be used in place of the 86-88 1227170. The original PROM has a silver sticker on it with the printed three or four letter code that would have also been on the outside of the ECM. If the sticker is in place, most likely the ECM has the stock program.

You can use either SERV # as a replacement, but you can't swap the prom from a 1226869 to a 1227170 and vice versa. So if your programming is stock, you can pick up an MT or AT (depending on which you have) 1227170 or 1226869 and use it as a replacement. The two computers are pretty much the same. The programming over the years is pretty much the same also. The only difference to be looking for is to use an MT or AT prom to match if you have an automatic or manual. There are differences in the engine programming, but the big difference is the AT Prom will send a signal out to lock up the torque converter, and the MT uses the same output to activate the SHIFT light. So if you have an AT, the torque converter will not lock up and your engine will be reving higher than it should.

If your prom is not stock, then look for the 1226869 and move your custom programmed prom to the replacement ECM.

Awesome, thanks for all of the help so far. I'll take a look and see what PROM is in there and go from there.

Also on a different note, I did notice yesterday while I was tinkering that while the pump wouldn't prime when I first turned the key, it would after I actually engaged the starter for a moment, as soon as I let off the start it would prime, then again if I hit the starter and let off again. Does that make sense?

Last I checked my fuel pressure was a bit low, in the mid 30's. So yes that is probably what is causing the stalling. I just thought it was weird that out of the blue the pump started not priming and then that same day I started getting the stalls... I figured I'd look into the relay/ECM before committing myself to a tank drop.

The original PROM for an 85 4 speed manual transmission car is FTY9355.

That's probably what the number was, I couldn't remember by the time I got back to the computer.

quote Originally posted by OriginalDoug: That's probably what the number was, I couldn't remember by the time I got back to the computer.

Back in ancient times we used archaic items such as a paper and pencil.

There is an oil pressure switch that ALSO will turn on the fuel pump. Redundant but wtf. Later years (not Fieros) dropped the oil pressure switch and just relied on the relay.

Yes stock ECM. Stock Prom. Most who ran the 3.4 used the stock ECM and it works OK. So you should be able to use any 85-88 stock manual transmission ECM, either SERV number, along with the stock PROM that comes with that ECM and it should function for you.

Ha! yes I should've written it down, I stupidly thought I'd be able to remember it.

Thanks for all the help, I'll pick up a new ECM when I find a good deal on one and see if that fixes the priming issue.

Going to do the plugs and see if that helps the stall issue at all.

If not I guess I'll have to drop the tank and either replace the pump or the little hose that disintegrates in there. Hopefully that will fix the fuel pressure issue.

1986 V6 4-Speed Fiero

I had this problem also. Initially, the fuel pump would not prime, so, after a few engine revolutions from trying to start the engine, the oil pressure switch activated the fuel pump relay. To alleviate the problem, I installed a momentary push button on the green wire running 'from' the ECM to the circuit and activated the fuel pump manually when I first started the car.

Now, I cleaned the engine yesterday, and now, the engine will not start. I no longer get the fuel pump to activate when oil pressure is up. I can still manually activate the fuel pump with my momentary push button. I can also run 12VDC to the brown/white wire at the oil pressure switch connector and get the fuel pump to activate. I can also, with the fuel pump relay removed, run 12VDC to the brown/white wire at the relay connector and activate the fuel pump. I can also run 12VDC to the brown/white wire at the ALDL connector and activate the fuel pump.

Now, since the oil pressure switch does not activate the fuel relay, and the relay does not activate when the oil pressure builds up, could it be that my fuel pump relay has become defective? The engine turns fine, when I put a little starter fluid in the intake housing, I get a start-up attempt, but the engine does not catch.

Does anyone have a solution?

I will replace the relay on Monday. It is a new relay (about 5 months old)

Question:

Can someone walk me through the circuitry that activates the fuel pump relay when the oil pressure switch reaches the required pressure to activate the fuel pump relay? I want to test the circut at each step to determine if I have a bad circuit or a bad relay.

The OP sender has a pressure activated switch the turns on the FP.
It does not turn on the relay, it is wired in parallel with the relay.

KEY - ON should show momentary battery voltage at ALDL D if relay is energizing.
If no voltage, try cranking the engine. If you see voltage at ALDL G, the OP switch is supplying voltage to the pump.