Fuel Pump / Relay weirdness (Page 1/2)
OriginalDoug SEP 13, 08:28 PM
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)

http://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: http://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).]

Gall757 SEP 13, 09:22 PM
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).]

OriginalDoug SEP 13, 10:02 PM
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?
phonedawgz SEP 13, 10:08 PM
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.

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phonedawgz SEP 13, 10:11 PM
Backprobe A1 of connector 2. It will be a Dk. Green/White wire. The ECM should supply +12v on the terminal when it thinks the fuel pump should be on. That would be for the first two seconds after the key is turned on, and when it sees ignition pulses (ie the engine is running) and for two seconds after the last ignition pulse. The Dk. Green/White wire runs from the ECM connector directly to the Fuel Pump Relay connector.

It isn't totally uncommon for an ECM to loose the transistor that controls that circuit.

Used ECMs being fairly cheap, you should be able to just replace the ECM with a different one for something like $20 plus shipping.

Edit
https://www.ebay.com/sch/i....1227170+ECM&_sacat=0

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

OriginalDoug SEP 14, 08:57 AM
Awesome thanks for the replies Phonedawgz, I will check the voltage on that wire tonight and see what I come up with.
theogre SEP 14, 12:39 PM
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

OriginalDoug SEP 14, 07:04 PM
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?
Gall757 SEP 14, 08:35 PM
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).]

phonedawgz SEP 14, 09:16 PM
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.