mgags7

Here is the scenario: OBD1 distributors have the ckp, tdc, and cyp sensors all built in. They all read off the exhaust cam, and they go as follows



Tiny pic but you get the idea.

CYP is the first pickup you see with the cap off, it has one point on the shaft that it reads off, to tell the ecu when the #1 cylinder is at TDC.

Underneath the metal plate, there are the other two pickups.
The TDC sensor has 4 points, it tells the ecu when any one of the four cylinders is at TDC.

The CKP sensor reads off 24 points, it tells the ecu exactly where in the rotation the crankshaft is, and will contribute to the random misfire CEL.

On obd2 cars the CKP and the TDC sensors are located on the oil pump housing, and the CKP reads off 12 points, because the camshaft is turning at half crankshaft speed.

I just ran the 4 wires for these two sensors up to the obd1 distributor.

If the engine misfires, the crankshafts position will not be like it normally is after a spark firing, it will lag behind some as it waits for the next cylinder to fire and keep it going. Basically, it fluctuates slightly. The obd2 ecu reads the signal from the CKP and generates the random misfire codes that me, and some other obd2 people who did the wiring conversion get.

I did check my wires and they have zero resistance back to the ecu, so they are not the problem here.

This has happened with multiple distributors so that isn't the problem here either.

My valves are well adjusted, my EGR ports are clean, my ignition timing is fine. The car really isn't even misfiring when the code flashes, or at least it is so subtle that you can't tell.

The code ALWAYS happens on the highway, it will not flash at low rpm, it usually always happens between 3500 and 4000 rpm and a light to moderate load. Going uphill or hitting it lightly to change lanes will cause it to flash.

This isn't a huge problem, other than you cannot pass obd2 inspection here with a CEL on. If it comes down to it I can just drive around at low rpm until the car's readiness codes are set, then go get it inspected. First though, I would like to figure this out, i have a buyer for my car but he wants the CEL gone....

Switching to the obd2 stuff is my very last option here. I do NOT want to deal with taking all that **** off the side of the engine, buying an oil pump and sensors, putting all that **** in. Then I would have to buy an obd2 distributor, undo my wiring changes, get the external coil, ugh it would be a nightmare.

Thanks guys
-Matt

mgags7

bump

anyone?

JBirch_97Prelude

I think you should post this in the tech forum. Maybe someone there has an idea of what to do.

jdmlude5

that is the same why.my lude is a 96 i jus ran the wires to the obd1 dizzy. with no probs.

mgags7

so you run an obd2 ecu and get no CEL?

Jim Truett

Pulse count from the reluctor wheel in the distributor should theoretically be the same compared to the crank reluctor. The problem here looks to be pulse duration. I don't think there is a simple way around this without software modification to the OBD-2 ECU.

mgags7

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Jim Truett &raquo;</TD></TR><TR><TD CLASS="quote">Pulse count from the reluctor wheel in the distributor should theoretically be the same compared to the crank reluctor. The problem here looks to be pulse duration. I don't think there is a simple way around this without software modification to the OBD-2 ECU.</TD></TR></TABLE>

That was the answer I almost knew was coming but didn't want to hear.

Thanks for your help.

JBirch_97Prelude

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Jim Truett &raquo;</TD></TR><TR><TD CLASS="quote">I don't think there is a simple way around this without software modification to the OBD-2 ECU.</TD></TR></TABLE>
Is it possible to modify a OBD2 ECU?

Jim Truett

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by JBirch_97Prelude &raquo;</TD></TR><TR><TD CLASS="quote">
Is it possible to modify a OBD2 ECU?</TD></TR></TABLE>

Yes it is, but not in a cost effective manner with commercially available equipment.

mgags7

So Jim, do you agree that it is the sensor causing the code to be stored? What else could do that? Knock sensor?

PirateMcFred

Does the misfire CEL narrow it down to a specific cylinder? If so is it consistantly one cylinder or is it different ones?

If it's a particular cylinder can you move your exisiting injectors around and get a different cylinder to misfire? Can trade out the injectors all together to a set that you know don't have issues with the misfire? Maybe yours don't flow very consistently and one cylinder is running lean?

What's the condition of your O2 sensor? Is it different than OEM? Old?

What's your spark plug gap? When's the last time you changed out your wires and plugs? What heat are they? Are they hotter or colder than stock?

What's your spark coil's condition? Have a spare to trade out just for testing? What happens if you retard your ingition timing an additional few degrees to see what that does?

What's the condition of your PCV? Could it be pulling in oil/blow-by and causing a misfire?

Have you tried different gas? Maybe you got a bad tank? Burn most of it off and then dump in some toluene (from a paint supply store) into 5 gallons and see if a real high octane does anything.

When did it start misfiring in the first place?

Pirate

mgags7

The misfire is never specific to any cylinder, it is completely random. In that respect, I don't think it has anything to do with one bad injector (or a few).

There is a nearly brand new denso OEM replacement o2 sensor in there, fresh ngk oem plugs gapped to 1.1mm.

The coil should be fine, but I can try another distributor again I guess, I posted above that this problem has gone between multiple distributors now.

I haven't tried retarding the timing, but as I said, the car isn't actually misfiring, it just flashes the code. I'll check the pcv but it is fairly new as well.

I try different gas every time I fill up, so I don't think it has anything to do with any one station. I always use 93 octane so I don't think that is the problem either.

It has always done this with the obd2 computer since I originally did the swap, and I never cared because driving at low rpms for a while was enough to get it inspected then switch back to obd1. But I can't exactly sell it like this to anyone hoping to pass a scan that doesn't really know what they're doing.

I put some fuel system cleaner in two tanks ago, and I don't think it liked that stuff, because it seems to have thrown this code more when that was in there. It didn't do it this morning at all, and normally would, so maybe one of the small things I did took care of the problem. I need to fix a loose vtak wire to get rid of the CEL, and I'm going to put a new fuel filter in it tonight, then reset the thing and see what I get.

Thanks for the help.

bluedlude

in some reading i was doing on ignition setups for my ME senior design project i saw somewhere that cam pickups are not preferred because they give off a relatively low signal and that it can cause misfires. not sure where i read it, ill have to try and find it again. maybe electromotive or something.

00BaseRacer

I have a 00 Lude. I suffered with the "random Missfire" codes for several months and tried everything to get it fixed. I ended up changing the ecu to obd1 and have never set another misfire code! Obd2 set up with conversion harness to obd1 ecu. Don't know if that helps. Wes

mgags7

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by 00BaseRacer &raquo;</TD></TR><TR><TD CLASS="quote">I have a 00 Lude. I suffered with the "random Missfire" codes for several months and tried everything to get it fixed. I ended up changing the ecu to obd1 and have never set another misfire code! Obd2 set up with conversion harness to obd1 ecu. Don't know if that helps. Wes</TD></TR></TABLE>

Yeah I know that works, I just need obd2 working for my inspection.

bump

JBirch_97Prelude

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by 00BaseRacer &raquo;</TD></TR><TR><TD CLASS="quote">I have a 00 Lude. I suffered with the "random Misfire" codes for several months and tried everything to get it fixed. I ended up changing the ecu to obd1 and have never set another misfire code! Obd2 set up with conversion harness to obd1 ecu. Don't know if that helps. Wes</TD></TR></TABLE>
Your car is illegal! We need a legal resolution!

mgags7

up

Jim Truett

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by mgags7 &raquo;</TD></TR><TR><TD CLASS="quote">So Jim, do you agree that it is the sensor causing the code to be stored? What else could do that? Knock sensor?</TD></TR></TABLE>

I really don't believe the knock sensor would have anything to do with this. I believe that the waveform of the pulse that the ECU is looking for is far different coming from the distributor reluctor, compared to the crank pickup. I would need to look at both waveforms on an oscilloscope to tell you for sure. Where are you located? I have access to a fully functional '99 Prelude and I own a scope. Maybe I could help you out.

superturboprelude

i think you hve one of teh wires swtich or in the wrong pins on teh distributor plug on the harness side when you rewired it i has this problem til i double check my wiring it went away

mgags7

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Jim Truett &raquo;</TD></TR><TR><TD CLASS="quote">

I really don't believe the knock sensor would have anything to do with this. I believe that the waveform of the pulse that the ECU is looking for is far different coming from the distributor reluctor, compared to the crank pickup. I would need to look at both waveforms on an oscilloscope to tell you for sure. Where are you located? I have access to a fully functional '99 Prelude and I own a scope. Maybe I could help you out.</TD></TR></TABLE>

If I had an oscilloscope I would have been all over it, I'm in NC. If you're anywhere near there I'd love to see the waveforms.

Again, thanks

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by superturboprelude &raquo;</TD></TR><TR><TD CLASS="quote">i think you hve one of teh wires swtich or in the wrong pins on teh distributor plug on the harness side when you rewired it i has this problem til i double check my wiring it went away </TD></TR></TABLE>

You had this specific problem? The car normally ran fine but you only had the misfire code at 4k rpm. I'm going to double check to be very sure. Thanks for the post.

JBirch_97Prelude

Yo mgags7, how long does it take for your OBD2 ECU to reach readiness from OBD2 diagnostics when you keep it under 4000 rpms. I am trying to figure how to beat inspections now, so that I am ready next year because it seems like there is no answer to the problem. I do not want to go OBD1, so this is my only solution.

mgags7

Due to my car being a 96, the law in NC allows me to only have 2 readiness codes set. I have had it ready in less than 10 minutes before.

JBirch_97Prelude

I guess I need to find out what Pennsylvania's law is on that. The last inspection I had did not pass because they said it had to be fully ready.

preludeSRV

You guys with the random misfire code...do you get rough start ups when the engine is cold? and you can hear the misfire from the exhaust and when the car is all warmed up it goes away?