Turn but no start

[Rolandtd]

Hello everyone first post here. Recently got a 98 Mazda b4000 4.0. A couple of times it wouldn't crank up but if i kept trying itd start up,so I talked with a buddy who told me it could be a bad ground so i tested which was ground and tan another ground wire in. Tried starting it and got a spark at the box and it won't start up at all just turns over I pulled the fuse box out where the relay is looking for loose connections which it did have since the diodes and resister do not want to go back in I can feel and hear the relay kick In but it's still not starting. I checked the fuel pump switch it wasnt tripped. I'm thinking the pump is now trashed along with the fuse box under the hood.

My question is can the fuse box be easily replaced since the connectors for the diodes and resistor doesn't want to seat and could my problem not be the pump but something worse.

Any help would be great thanks in advance

 

[alwaysFlOoReD]

Hello everyone first post here. Recently got a 98 Mazda b4000 4.0. A couple of times it wouldn't crank up but if i kept trying itd start up,so I talked with a buddy who told me it could be a bad ground so i tested which was ground and tan another ground wire in.
From where to where?

Tried starting it and got a spark at the box
What box?

and it won't start up at all just turns over I pulled the fuse box out where the relay is looking for loose connections which it did have since the diodes and resister
If you're talking fuse box I don't think there is any diodes or resistors in the fusebox. The fuse box holds fuses and relays.

do not want to go back in I can feel and hear the relay kick In but it's still not starting. I checked the fuel pump switch it wasnt tripped. I'm thinking the pump is now trashed along with the fuse box under the hood.

My question is can the fuse box be easily replaced since the connectors for the diodes and resistor doesn't want to seat and could my problem not be the pump but something worse.

Any help would be great thanks in advance

Perhaps some pics of the areas you're talking about would help us figure out where you're talking about.

 

[RonD]

Welcome to TRS

If starter motor is working then do 50/50 test
Pull off the big air tube on the intake, screw driver needed
Open throttle and spray gasoline or Starting Fluid(ether) into the intake

Try to start the engine

If it starts and then dies you have a fuel delivery problem, i.e. fuel pump or fuel injectors

If it doesn't start then you have spark or compression problem

50/50

 

[Rolandtd]

Thanks for the responses alwaysFlOoReD and RonD, I ran the ground from a ground bolt under the hood to the ground on the fuel pump relay. The box that the spark occurred was the under hood fuse box around the ignition fuse which wasn't blown which was weird, and i think they might be resistors since they're not fuses ill post some pics in the morning when I get off work

RonD I did spray starter fluid in the throttle body it tried to fire up but didnt

 

[RonD]

When you turn on the key the CEL(check engine light) should come on, does it?
CEL on means computer(PCM) is powering up.

If not then the PCM Relay in engine fuse box, is not closing with Key ON
Check Fuse #19(25amp) in engine fuse box
Fuse 19 power also powers Coil Pack, Red wire
And fuse 19 power runs thru a diode to power the the PCM Relay to close it
If PCM Relay doesn't close then there will be no spark and no fuel injector pulses

Fuse #8, 30amp, powers the computer(PCM), and fuel injectors when PCM relay is closed

 

[Rolandtd]

The CEL was not coming on I checked the number 19 fuse it was good but my test light was very dim on it I changed it anyways and the truck started right up. So any idea what caused the truck to not want to start before I started messing with it?

Also thank you for the help and getting me on the right track

 

[RonD]

Good work

Fuse prongs/clamps can get corroded, as can the wires connected to the underside of fuse panels.
Sometimes just pulling out a fuse and sticking it back in cleans the connections enough for full voltage to pass thru.
Same for relays

Corroded connectors reduce the voltage in the circuit, so 12 volts in might end up as 7 volts out, for the Coil Pack that would be a VERY weak spark


4-stroke engines need 3 things to start up
1. spark, at the right time
2. fuel, in correct mix with air
3. compression

You are missing one or even two of these when you have a No Start
50/50 test is quick way to tell if it is spark or fuel, it is usually fuel with Fuel injection engines

Compression above 100psi is needed because liquid gasoline won't ignite using a spark, yes the movie guys get that part wrong, lol.
When you compress the air/fuel mix you HEAT it up, this causes gasoline to vaporize, and this vapor can be ignited by a spark.
Compression is either good or bad, can't be intermittent, like spark or fuel

So after 50/50 test it is often best to check a few cylinder's compression just to take it off the table or confirm it IS the problem so you don't waste time and money on chasing a spark issue.
Most vehicle engines will have 150 to 170psi, nothing close to 100psi, so quick test is all that is needed

 

[Rolandtd]

Thanks for the tips. I'll pick up a compression tester when I can. I did have no start problem yesterday I pulled the fuse and put it back and it started right up, looks like I'll be cleaning the terminal.

 

[Rolandtd]

Well it's happened again no start, I found the Schrader valve and it is getting fuel and isn't getting spark.

 

[RonD]

Test port on fuel rail with pressure means system is holding pressure, but not that the engine is getting fuel via the injectors

Spark AND injectors are controlled by the computer, 1995 and up.
Computer doesn't "know" when you want to start the engine, it has no link to starter motor.
Computer will start spark and injectors when Crank Position Sensor(CKP) starts to send it timing pulses, crank shaft is spinning.
CKP sensors rarely fail, not never, but rarely, check its connector, 4.0l OHV CKP is located at about 10:00 passenger side of engine next to crank shaft pulley.

BUT.............do this first, crank the engine a few times, pull out a spark plug, any one of them, look at its tip, if fuel injectors are working it will be WET with gasoline
DRY spark plug and No Spark means computer does not "know" you are trying to start the engine.
This could be a computer issue or CKP/wiring issue

If spark plug is WET then computer and CKP are working
Coil pack gets power on a separate fuse than computer
You can check the Red wire on the coil pack for 12volts with key on

 

[Rolandtd]

Thanks for the info I went to start it after 9 hours and it started up after a moment. Next time it does this ill check everything you've mentioned. I also picked up a coil pack and ill put ot in next time to see if it changes things.

 

[Rolandtd]

Well it wasn't starting earlier I checked the plugs they were dry so I crawled under and tapped the crank sensor with a small hammer and it started right up. Looks like I'll be picking up another sensor

 

[RonD]

Good work

Yes, you broke it with the hammer, lol

 

[Rolandtd]

Lol. I'm going to wait until it does it again to double check my findings. I'll report back with results. Also thanks so much for the help.

 

[Rolandtd]

Well after a few weeks new coil pack crank sensor and tune up truck hasn't had an issue. Thanks for the help everyone