10 Amp Engine fuse on an 89 FI

[gunnerw]

The problem is that right now if am to drive it I will have to leave the alternator disconnected or I will continue to blow the 10a engine fuse.

[dalebwilson]

Ok I misunderstood. You will have to get your hands on a good alternator to know for sure.


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[gunnerw]

Yeah, Getting ready to order on from RockAuto now. Thanks for all of your help Dale.

[dalebwilson]

You're most welcome. I hope you are up and running well soon.

[gunnerw]

Well the new alternator came in, I installed it threw a new 10a fuse in the engine slot, cranked the engine, it started and ran for about 20 seconds and blew the fuse again. I thought I had this figure out. Any more ideas anyone?

[bravekozak]

Try changing the main relay. The main relay is different than a regular relay. It has a resistor across the solenoid.

[tooldude]

Question gunner, is this a problem that developed recently, or did the car already have this problem when you got it? The previous owner could have tapped voltage for something, like that radio, at a point where it's going through the engine fuse. If not, I would look first at the fuel pump relay since that is your most recent change. It could be out of spec or even the wrong part. Typical resistance of its type of coil, on Festivas, is about 40-60 ohms & 225 -350 ma. [Relay out & at corresponding (by color) terminals, there should be resistance between BK/R to GN/Y** and BK/W to BK only - If BK/W is connecting to any other terminal, the fuel pump is pulling some of its amps through the Eng Fuse - a short.**The relay contacts are a second **GN/Y that should not have continuity to BK/R with relay unpowered, & no GN/Y to **GN/Y] Apparently you have no schematic and this area is unique to the 1989 EFI. Voltage(+) coming from the Ign switch B/W wire has a splice point where 12V branches to the cooling fan relay, Ign coil & Ign module (also B/W wires), & 10A Engine Fuse. With the Eng fuse removed and Ign Switch on, you can find 12V(+) on the fuse box terminal which is on the Ign Switch side. Ignore that one, nothing on that side can cause increased amps through the Eng Fuse except an over-charging Alternator. Your problem starts at the other fuse terminal. That terminal supplies 12V to the fuel pump relay COIL (from a splice point), main relay COIL, and the alternator regulator circuitry, these all being B/W wires. You need to know which one you're dealing with. That is all that should be in the circuit. To check that entire part of the B/W harness at once for a short, remove Eng fuse, main relay, fuel pump relay, and Alt connector (B/W). Now that harness should be isolated from everything - nothing between ground and any B/W wire (at relay or fuse box connectors). Check with the ohmmeter on Low scale for an infinity or OL reading. With this check, finding a short could be from wiring, or in the fuse box, otherwise a short could be at one of the connectors, or, yes, in the alternator ("new" parts can be defective).

[F3BZ]

just FYI if you still want to replace the main relay, or someone else might be interested. even though it says for Mazda, it is the relay used in the festy.

http://www.ebay.com/itm/NEW-NOS-Mazda-Main-Relay-Fuel-Injection-B2200-B2600-1989-1993-/191344619891?vxp=mtr

[nitrofarm]

Try changing the main relay. The main relay is different than a regular relay. It has a resistor across the solenoid.

Brave is correct and after looking at the circuit I'm thinking that relay is designed to run @ 9 V. If the relay has failed internally,it may not be creating ANY resistance.Then the Main relay may be drawing to much current once you STOP cranking. Thats why I'm thinking it starts, then blows. I personally would have replaced it as soon as I saw its really the only thing in that circuit. But I'm glad this thread is here because I would never even looked that close at the schematic to see the resistor was there!

[tooldude]

The fuel pump relay is in that circuit also, there are 2 relays in it, running in parallel. Also, the FP relay starting winding is not depicted as dropping out as with the other year models. I believe that is correct, as it is shown without the RC components of the later models, and the way it's shown in the schematic it could only be removed mechanically with another set of contact points-seems unlikely & not depicted. Both relays are running on full system voltage as the resistor in the main relay is in parallel with the coil which splits amperage not voltage. As that same B/W wire feeds into the V Reg circuitry in the alternator, I believe the resistor is a typical clamping resistor as used on coils to protect the solid state circuitry from voltage spikes off the coil. The FP relay has 2 windings and twice the chance of a bad coil. A simple current/resistance check at the relays should catch a bad one.

[nitrofarm]

Tool you are misunderstand what I'm saying. That 10 amp is only protecting that Main relay. And if you suspect the Fuel Pump Relay you so much my do a Fuel pump test with the jumper by the brake booster. No need to check resistance etc. Nitro

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[tooldude]

Nitro, he said it's a 1989 FI on his first post and I'm looking at the 1989 EVTM. It's different-the B/W wire is running both relays and the FP coil for startup apparently doesn't kick out after startup as 90-93. Both coils run all the time so the FP never drops out temporarily if the VAF shuts on deceleration as explained in the FSM. From 90 - 93 they used the RC (resistor/capacitor) setup for that so as not to run both coils. I'm not favoring any possibility but pointing out the odds of 2 FP coils to 1 Main coil. As you said, the coil could be shorted, applies to all 3 coils. BTW, the jumper test only tests the 1 coil that the VAF controls, missing the one used for cranking. Actually, if you see the schematic for '89 you won't need my explanation. I try to offer ideas to avoid throwing part$ at problems; personal opinion but even wrong ideas cause thinking that can lead to solutions. Printed messages with no tone or inflection are tough too, and I'm not sure what is considered too large a post. Condensing them too much limits explanations.

[nitrofarm]

Tool please scan and post the Schematic you are refering to. Thanks, Nitro

[tooldude]

My printer/scanner broke a while back. My wife's phone is a stupid Windows phone, don't know if it will do it, I'll check when she gets in later. I bet someone has the 1989 EVTM & could scan it, pgs. 40 & 41.

[nitrofarm]

Ok, I still would like to see him do a simple Fuel Pump Test. That would eliminate the Fuel Pump Relay & Pump.