</o:smarttagtype><!--[if gte mso 9]><xml> <w:WordDocument> <w:View>Normal</w:View> <w:Zoom>0</w:Zoom> <w:PunctuationKerning/> <w:ValidateAgainstSchemas/> <w:SaveIfXMLInvalid>false</w:SaveIfXMLInvalid> <w:IgnoreMixedContent>false</w:IgnoreMixedContent> <w:AlwaysShowPlaceholderText>false</w:AlwaysShowPlaceholderText> <w:Compatibility> <w:BreakWrappedTables/> <w:SnapToGridInCell/> <w:WrapTextWithPunct/> <w:UseAsianBreakRules/> <wontGrowAutofit/> </w:Compatibility> <w:BrowserLevel>MicrosoftInternetExplorer4</w:BrowserLevel> </w:WordDocument> </xml><![endif]--><!--[if gte mso 9]><xml> <w:LatentStyles DefLockedState="false" LatentStyleCount="156"> </w:LatentStyles> </xml><![endif]--><!--[if !mso]>******** classid="clsid:38481807-CA0E-42D2-BF39-B33AF135CC4D" id=ieooui>*********> <style> st1\:*{behavior:url(#ieooui) } </style> <![endif]--><style> <!-- /* Style Definitions */ p.MsoNormal, li.MsoNormal, div.MsoNormal {mso-style-parent:""; margin:0in; margin-bottom:.0001pt; mso-pagination:widow-orphan; font-size:12.0pt; font-family:"Times New Roman"; mso-fareast-font-family:"Times New Roman";} @page Section1 {size:8.5in 11.0in; margin:1.0in 1.25in 1.0in 1.25in; mso-header-margin:.5in; mso-footer-margin:.5in; mso-paper-source:0;} div.Section1 {page:Section1;} --> </style><!--[if gte mso 10]> <style> /* Style Definitions */ table.MsoNormalTable {mso-style-name:"Table Normal"; mso-tstyle-rowband-size:0; mso-tstyle-colband-size:0; mso-style-noshow:yes; mso-style-parent:""; mso-padding-alt:0in 5.4pt 0in 5.4pt; mso-para-margin:0in; mso-para-margin-bottom:.0001pt; mso-pagination:widow-orphan; font-size:10.0pt; font-family:"Times New Roman"; mso-ansi-language:#0400; mso-fareast-language:#0400; mso-bidi-language:#0400;} </style> <![endif]--> New guy, need expert advice!

My Mazda B3000 will crank strongly but not start. Ran great all day, filled it with gas, sprayed off the road salt at car wash, and parked it. Next day, no start. Here’s what I know (mostly due to advice on this site!):

• Can hear fuel pump running at start, fuel pressure at rail about 55psi. Dumped ispopropyl in full gas tank in case of water, replaced fuel filter.
• No spark, even with new plugs, wires, and coil pack (all tested with resistance in spec)
• Crankshaft position sensor tested fine, replaced it anyway, no change
• Cam position sensor tests okay (resistance and signal in spec)
• Wire harness between these sensors and PCM showing continuity
• PCM grounds all good
• Wire harness between coil and ECM showing continuity
• 12 volts to coil pack, but no circuit completion between hot and the 3 primary coil connectors when cranking engine (checked with test light)
• When connecting OBD2 code reader, no codes (I may have cleared them when I disconnected harness to PCM before testing) but can see some sensor data (temp, RPM, air flow).
• Passive anti-theft light goes out when cranking.
• Pulled PCM, looks clean, no burns (but a little moisture at pin connector)

Is there anything obvious that I’m missing or can try before deciding it must be the computer? Been wrangling this slowly since December, and any assistance will be greatly appreciated.

 

Welcome to FTE.

Boy you've been busy with this one.

Good trouble shooting so far.

With B+ 12 volts to the coilpack at KOEO, it kinda sounds like the computer has lost it's ground switching for the coil pack.

When you go from Off to Run, with the ignition key, before cranking the engine (KOEO), do all of the dash warning lights come on for their self test????

If you come to suspect the computer, most autoparts stores can do a no cost bench test on it.

A slavage yard for an exact P/N replacement, will likely be less expensive than a reman or new one.

I'd have any replacement computer bench tested before using it.

Let us know what you find.

 

You might try testing for continuity the 3 wires that the PCM uses to ground/fire the coils. On your 2001:

- Coil #1 (TN/WH) runs to PCM Pin #26

- Coil #2 (TN/OG) runs to PCM Pin # 52

- Coil #3 (TN/LG) runs to PCM Pin # 78

 

Rockledge - I have continuity on all three coil to PCM wires and 12V to coil. When cranking with a test light between B+ and each of the coil to PCM wires I get no light. So...

Pawpaw- I agree, somehow the coils aren't switching to ground. I checked the dash lights, and when I go to key-on I get the following:
ABS light on- goes out quickly
Airbag light - goes out quickly
"Check gauge" light - goes out
Seatbelt and battery lights
Check Engine light (stays on, but goes out when cranking)
PATS (anitheft) light flashes with key in, goes out with key-on

All of the above lights came on except for Check Engine and PATS without the PCM installed as well. So it looks like computer is self-checking? With OBD scantool I connect up fine, get no codes, and can see realtime sensor data (RPM, throttle position, temps, air flow, etc.)

Did a little more checking, seems all PCM relay/diode/fuse are good. PCM really looks clean and new with no burns or cracks, but I'm running out of other explanations. When you say autoparts stores can bench test, any stores in particular? I called the Ford dealer and they won't do it. Bless their hearts.

 

Lets think about this some more.

On the KOEO self check, if the CEL is staying on & not timing out like the ohers, it seems to me there should be a code stored.

I'm not clear on your check of the coilpack ground wires.
When you were testing the above three wires for continuity, was that while you were cranking the engine, or was that a static test without the engine being cranked & was the reading between a wire & ground????

Normally these wires should be open circuit to ground, until the computer gets a crank or cam shaft signal, to turn the ground on at the right time to cause the coilpack to fire the spark plugs at the right time. So the test light should blink as the engine is cranked.

With having B+ at the coil pack, the test light not switching on when your testing between B+ & each of the above coil pack to computer ground wires when cranking the engine, it sounds like maybe the computer ground switching drivers, have a problem.

Not likely that all three coil pack wires, or connector contacts would go bad at the same time.

Edit: Are the fuel injectors firing????

Advance Auto & AutoZone in my area will bench test the computer at no cost.

If it's bad, we need to ask what the heck would take the computer ground switching drivers out, if thats what's bad????

 

pawpaw - thanks so much for pondering all this!

It does seem there should be a code, but I pulled the computer before I had a scantool, so I may have erased them. No codes at all now.

I've done three tests on the wire harness between the coil packs and the PCM:

• Harness unplugged at both ends, checked wire continuity connector to connector with multimeter (audible continuity check). All good.
• All grounding pins on PCM connector tested to ground with audible cont. check. All okay.
• Harness connected to PCM, unplugged from coils, checked ground on each of the three coil leads with test light from +. No light blink on any of the three.

Just got noid light on the way home tonight, and I do have signal going to fuel injectors (as well as normal fuel pressure).

So the only identifiable problem seems to be coils not switching to ground leading to no spark (despite crank and cam sensors testing fine)? Otherwise computer seems to be acting normally.

Visited both Autozone and Advance, both will pull codes but can't bench test PCM. I may have a lead on someone who can however. Wonder if a non auto computer tech could do basic bench troubleshooting? In looking at the PCM board, there are three big, prominent transistors that would seem to be likely culprits, not to hard to test if one had the basic electronic skills. I will check this out tomorrow. If it is the PCM, repairing mine would seem to have some advantages over a reman (no programming issues at the dealer). Of course, if it is the PCM that still doesn't address your point about the initial cause of damage (which could logically be repeated).

Any other possibilities I'm overlooking? I'm wide open to checking additional stuff (or rechecking if anything is unclear).

 

OK , more good trouble shooting & feedback.

Now on the last of the above 3 tests, was the engine being cranked when you had the test light connected between the B+ pin & a ground pin at the disconnected coil pack connector????

As these grounds are normally open circuit, until the engine is cranked, so the computer gets a cam & or crank sensor signal to close the ground connection, the light won't be on, unless the drivers are shorted inernally.

So you'll need to crank the engine to see the test light blink.

Your above test does say that the drivers aren't shorted, because if they were, the test light would be on at KOEO.

Seeing as how the Noid light says the fuel injectors are working, it says the computer is getting & recognizing the cam sensor PID, so even if the crank sensor were bad, the limp home mode would have the computer use the cam sensor's PID to operate the coil packs ground drivers.

So it seems you've found yet another clue that the coil packs ground switching is bad for some reason & yup if so, we don't know what may have caused it.

Have you taken the coil pack in for a bench test????

 

My apologies, I gave a long answer without answering the question!

I tested the wiring harness attached to PCM, with test light at disconnected coil end and B+, and I did crank the engine. No blinking lights on either of the three wires.

The coil is new, I checked primary and secondary resistance (all in spec). The old coil actually appears to be fine as well. Since it appears there is no signal to the coil, is there still a need to have it bench tested?

Just to clarify, check engine light is on at key-on, engine off. It goes out when cranking. What does this say about PCM status?

 

OK, good feedback, so you Were cranking the engine when you tested at the disconnected coil pack connector with your test light & it didn't blink.

This too confirmes that the computer isn't providing ground switching for some reason.

At this point it sure suggests that there is a problem with the ground switching drivers themselves, but it still could be with their trigger circuit, or a circuit board connection to them, so we can't condemn them just yet, but you seem to have narrowed your suspect list down considerably.

Are there any signs of overheating on the circuit board, or of cold solder connections, or maybe a bad, or questionable looking race on the circuit board in the area of the ground switching component???? If so, have a look at the area under magnification.

I forgot that you had said the coilpack was new.
I was wondering about the old coil pack & if maybe it's primary winding had shorted out & had overloaded/overheated the ground switching circuit & maybe thats why it seems to have gone belly up????? So in the back of my mind I was still looking for a root cause for the no ground switching problem.
You wouldn't want to install a new computer, or your repaired one & have it taken out again.

It's not a bad idea for us to have a new electrical device bench tested before we leave the store with it, as I've seen bad new parts right out of the box & most stores won't accept a return on them if we've unpackaged & installed them!!!!

If there aren't any trouble codes stored, if I remember correctly, the CEL would come on for a self test, then time out & turn off.
So with it remaining on at KOEO, that made me think there is a stored code/s.

Maybe a vehicle computer guru will chime in & clarify.

 

That sounds normal. I don't believe the CEL times out w/ignition on and engine off, but instead, it stays on until the key is turned to the crank position. At least on my '98 it works that way.

 

timing chain or belt slipped or broken- take off oil cap and have someone crank while observing the valve train. If no movement of any valves you can see- your chain or belt has broken. Can't remember which this truck has. Compression test can also verify this. From everything else you looked at looks like fuel and spark are good

 

Yup your right about the CEL light Not timing out Rockledge, I checked my 99 this past weekend & it lights up at KOEO & stays lit until the engine is cranked.

So how is it going MazDoc????

 

Thanks again for the feedback, folks, decided to take a few days off to do other things (that don't involve electronics, fuel, or spark)!

I think timing chain should be functional as I get a signal from the cam position sensor when I crank (the sensor is driven by the cam shaft). I did attempt a compression check with generally acceptable results (some variation, likely due to iffy tester and really awkward access to plug holes). Remember, though, the one clear problem is no spark (due to no PCM ground switching).

At this point it looks like either sending PCM for testing/repair (since almost everything on it seems completely functional) or trying a junkyard used version. A friend is looking into the latter, and if that fails I'll try the former. I will let you know as soon as I have a result (hopefully next week). Thanks again for all the help.

Doc