Need help troubleshooting a miss

[mjlogan]

Background

88 Ranger, 2.9 5 speed. Fresh late model heads, no cat, recent high pressure fuel pump. About a month ago it started missing every once in a while like someone briefely pulled the coil wire and stuck it right back on. This went on for about a month until last weekend , i started it up one morning and it ran like it was only hitting on 5 cylinders. Every morning since then it will run like its missing a cylinder for about 5-10 min and then it will run fine (except with the previously mentioned miss). Every once in a while after its hot, it will feel like its dropped a cylinder again. When it runs good, it runs GOOD.

What i've done so far

Pulled codes (Using KOEO method with test light)
-67- i bypassed the neutral safety so no concern
-95- the fuel pump is on a toggle and has been forever, so no concern there
-29- i think this is the problem, but not sure since mine has no egr
-14- ignition pickup irratic- this is what i had originally thought, but it only threw a 14 once and im not sure i even read it right. I cleared codes, took it for a long drive, and it did not throw a 14 the second time.

Replaced Ignition Control Module (TFI)- no change
Replaced cap and rotor - no change
Plugs all look perfect (light brown)
Double checked/cleaned up all grounds
I'm going to put a fuel filter in it tonight, but doubt thats the problem.

My thinking is that it is something to do with the pickup inside the distributor. Any advice would be appreciated. Thanks

 

[IMenriched]

Background

88 Ranger, 2.9 5 speed. Fresh late model heads, no cat, recent high pressure fuel pump. About a month ago it started missing every once in a while like someone briefely pulled the coil wire and stuck it right back on. This went on for about a month until last weekend , i started it up one morning and it ran like it was only hitting on 5 cylinders. Every morning since then it will run like its missing a cylinder for about 5-10 min and then it will run fine (except with the previously mentioned miss). Every once in a while after its hot, it will feel like its dropped a cylinder again. When it runs good, it runs GOOD.

What i've done so far

Pulled codes (Using KOEO method with test light)
-67- i bypassed the neutral safety so no concern
-95- the fuel pump is on a toggle and has been forever, so no concern there
-29- i think this is the problem, but not sure since mine has no egr
-14- ignition pickup irratic- this is what i had originally thought, but it only threw a 14 once and im not sure i even read it right. I cleared codes, took it for a long drive, and it did not throw a 14 the second time.

Replaced Ignition Control Module (TFI)- no change
Replaced cap and rotor - no change
Plugs all look perfect (light brown)
Double checked/cleaned up all grounds
I'm going to put a fuel filter in it tonight, but doubt thats the problem.

My thinking is that it is something to do with the pickup inside the distributor. Any advice would be appreciated. Thanks

sounds like your on the right track.

Maybe you already done this?? IDK
If ...it is a bad plug....try pulling one plug wire off at a time...the one that you remove and shows no change in the running condition is the culprit.

To verifiy that it is just that one plug remove/swap suspected plug and or wire, switch it with a cylinder that you know is working...if the miss followes to the new location....you know for sure then it isn't random.

yes your pickup coil inside the distributor could be starting to give you fits. If it turn out the miss is random...then would lean that way. you'll have t remove the whole distributor to replace that. make sure the lower bushing for the internal shaft isn't ware too much. too much sloop can give you erratic spark.

you've already changed the TFI....so that should elimate it from the cluprit list. but would have it retested just in case. I had a new one that didn't go real far.

last but not least, double check for vacuum leaks.

 

[MAKG]

No, it's not right.

There are no ignorable codes. If the PCM is complaining, you have a problem to fix.

That 67 in particular prevents proper idling and aborts the KOER test. If you're getting it, you did NOT bypass the neutral switch (and it is NOT a safety switch unless your manual transmission has clutches, bands and a planetary gear).

You can't expect a control system to behave nominally if it is in off-nominal conditions. Hard codes put it in a limp mode. Doing this for a long time means the fuel trims are way off.

And doesn't it ring some alarm bells that you think you're getting an EGR code with no EGR?

And assuming new = good can very easily send you in circles.

 

[Zachalanche]

I've been getting some miss firing on really cold mornings until the engine warms up. It stumbles pretty bad during this period, but same as you when it runs good it runs great. I checked the codes and also got code 14. Im about ready to pull my ignition module and test it. Im interested to hear what your solution ends up being since I think we may have similar problems.

 

[mjlogan]

No, it's not right.

There are no ignorable codes. If the PCM is complaining, you have a problem to fix.

That 67 in particular prevents proper idling and aborts the KOER test. If you're getting it, you did NOT bypass the neutral switch (and it is NOT a safety switch unless your manual transmission has clutches, bands and a planetary gear).

You can't expect a control system to behave nominally if it is in off-nominal conditions. Hard codes put it in a limp mode. Doing this for a long time means the fuel trims are way off.

And doesn't it ring some alarm bells that you think you're getting an EGR code with no EGR?

And assuming new = good can very easily send you in circles.

Good information, thank you.

The EGR code DID ring a bell- like i said "i think this may be the problem".

The 95 code is thrown because i am running the fuel pump on a toggle.

I must have incorecctly assumed the 67 was due to me bypassing the switch that prevents the engine starting with the clutch let out

Are you telling me that in order for the PCM to get out of limp mode I need to put the fuel pump back on those 3 relays and put the clutch switch back on? I have had it hooked up like this for a year with no problems until recently

 

[MAKG]

Umm, your clutch has nothing to do with neutral. That's a transmission function.

The PCM will not throw an EGR code if it doesn't support EGR. The alarm bell is that YOU aren't decoding it correctly. Or else you put the wrong PCM in there.

It's possible that some of your problems are due to modifications, but certainly not known from the information given. You really shouldn't be messing with systems you don't understand and expect them to behave sensibly.

So, now, you get to figure out WHY the PCM is complaining. If you're comfortable with leaving codes alone, have someone else do the work. That's why you're in the fix you're in.

Frankly, I don't know where to tell you to start. If you were an experienced mechanic, I'd steer you to the Mitchell or Ford pinpoint tests. But you need to understand the systems to use those effectively. And you don't if you think not having a cat does anything but make the rest of us choke on your exhaust.

 

[mjlogan]

Umm, your clutch has nothing to do with neutral. That's a transmission function.

The PCM will not throw an EGR code if it doesn't support EGR. The alarm bell is that YOU aren't decoding it correctly. Or else you put the wrong PCM in there.

It's possible that some of your problems are due to modifications, but certainly not known from the information given. You really shouldn't be messing with systems you don't understand and expect them to behave sensibly.

So, now, you get to figure out WHY the PCM is complaining. If you're comfortable with leaving codes alone, have someone else do the work. That's why you're in the fix you're in.

Frankly, I don't know where to tell you to start. If you were an experienced mechanic, I'd steer you to the Mitchell or Ford pinpoint tests. But you need to understand the systems to use those effectively. And you don't if you think not having a cat does anything but make the rest of us choke on your exhaust.

Well, i will say thanks again for trying to help me- I can tell you are very knowledgable and are a valuable resource... but you need to chill out a little.

I am not an "expirienced mechanic", but i'm not an idiot either. The cat is temporarily removed because of the radius arm crossmember i built. It will be back in place shortly. Just figured it was information that may help diagnose the problem.

As far as i know, this is the stock PCM. I followed the instructions listed in the tech library here... twice... and got the codes i posted above. I will test it again tonight to make sure. I am trying my best to learn these systems. All i currently have to go on is a chiltons manual and the information on this site.

 

[MAKG]

The Mitchell books can often be found at the library (even in remote locations), or a nearby two-year college or vocational school with an automotive tech department.

I'd suggest making it as stock as possible for diagnosis. The radius arm crossmember won't matter, but the missing cat might, especially if the Y-pipe is just open to the air.

And just to check, when you made this crossmember, you didn't weld on the truck, right? If you did, and didn't remove the PCM, that could be a problem.

 

[holyford86]

the code 14 could be related to quite a few things, it could be a loose or broken wire, a bad idm resistor, a bad ignition pickup (inside the distributor), or a bad TFI module (I have found that the tfi modules are very sensitive to welding on the vehicle). Put your fuel pump back on a relay, if the relay doesnt work correctly check the wiring, Its unsafe to not have the fuel pumps on a relay, in case of an accident or fuel leak. The neutral sense switch code can be thrown if the vehicle is in gear while running the self tests, among other things, like loose wires or a bad switch. The code 29 is a VSS signal code, if the computer is original to the truck, check the vss for proper operation and inspect the wiring.

 

[mjlogan]

The dead cylinder problem was fixed after i threw a set of plugs and wires at it. Still havent discovered the occasional miss, but will post up if i figure out what it is.