Cobra st,t,t,tuters and high RPM

chasenichols · Jun 5, 2011

Cobra st,t,t,tuters at high RPM

So, car has always runs awesome, but the other day while getting on the freeway i noticed that it doesn't want to pull all the way to redline like normal. At about 4k it starts...missing? Not really sure how to describe it, but it does not have the power it should and it feel slightly rough. I can still pull it to redline, but there is definitely something wrong. At the same time the tach started to flutters up and down by about 100RPM all the time. Not a lot but enough that it is annoying and made me wonder if the two things were connected.

I did my research and concluded that it must be the PIP sensor since the tach seemed to be getting crappy reading (it gets it's reading of the PIP, right?). So i got a new one, pulled the distributor, and replaced it. Got the timing all set right, took it out for drive and there was no change.

Checked fuel pressure to make sure that was good. 30 PSI. Also i have A/F gage (narrow band) and it reads richer than normal at WOT (~11). All this points to an ignition issue i think.

Also pulled the codes and the only thing i got 172 (O2 fault/lean bank #1) for the KOER (key on engine running) test. KOEO passed and there was nothing stored.

I'm at a loss. What do you guys think?

1slow95 · Jun 6, 2011

My first thought was the PIP, next would be a problem with the ignition box (MSD) if you have one. Was the fuel pressure 30 PSI with or without vacuum? It should be 39-40 PSI with the vac line removed, around 30-32 with vac.

99FiveOh · Jun 6, 2011

If your tach is moving erratically it's definitely a problem with ignition since the fuel system has no control over the tach.

Did you buy that PIP sensor from Advance or Autozone? If so, take it off, take it back and buy this: https://www.napaonline.com/Catalog/...716_0306551154&An=599001+101994+50026+2026026

I too had your very same problem, and after swapping dizzies and PIP sensors FROM Advance auto parts, I was stumped! Even Napa's cheaper brand PIP sensor was giving me the same problem (it was the same crappy BWD brand as Advance had). So, the guy at Napa informed me that their Echlin line is OEM equivalent.

He was right, I installed that PIP sensor and it's still running after a year. Trust me on this.

chasenichols · Jun 6, 2011

Alright...thanks for the advice guys.

Fuel pressure was taken with the vac line on. But like Not said, should be an ignition problem. And i dont have MSD, still running the stock stuff.

I'll pull the new PIP off (it came from O's - 30 bucks) and replace it will the good one.

I'll post back when i finally get this thing running right.

revhead347 · Jun 6, 2011

NotA4.6 said:
Even Napa's cheaper brand PIP sensor was giving me the same problem (it was the same crappy BWD brand as Advance had). So, the guy at Napa informed me that their Echlin line is OEM equivalent.
.

Every parts guy is going to try and convince you that there stuff is the best and or OEM equivalent. Truth be told, Echilin is known for being one of the crap brands. You just got lucky.

Kurt

Chythar · Jun 6, 2011

How's the power feel below 4K rpm? If it feels like it's down you may have a dirty MAF. How does the engine idle?

chasenichols · Jun 6, 2011

The engine idles great. Down low it feels good. It still snaps sideways on dry in 1st and i get rubber on the shift to second (if this is an accurate measure of performance...haha!) But i maybe it should be better, hard to say without jumping in an equivalent cobra that runs like it should.

Anyway to test the PIP? Anything else that could be giving me (and the ECU) a crappy engine speed reading?

99FiveOh · Jun 6, 2011

Matt, dirty MAF won't cause the tach to flutter or skip.

Kurt, I was actually wrong in what I said, the guy at the Ford dealership told me to buy the Napa Echlin brand as it is made in the same factory as the Motorcraft one he had on his shelf. I was browsing O'reily's website and it shows they stock a Motorcraft PIP sensor for 64.00. That's cheaper than the dealer at around 100 bucks!

Either way, all the 20$ sensors are also made in the SAME factory, and for years now they have been failing right out of the box in reman'd dizzies. I've seen it happen way to many times (myself included). Also, when I bought the Echlin brand PIP sensor I noticed right away it was much better quality. The biggest difference is in the epoxy that they use to seal the wire connections into the sensor. I had one of the cheap sensors melt out all the epoxy! It would flake out of there with a finger nail... garbage!!!

toyman · Jun 6, 2011

I wouldn't assume that a small flutter in the tach points to an ignition problem. I can see where a bad injector or connection might cause the tach to bounce under load as the engine misfires. I would pull codes to see if there is a lean condition or an O2 sensor issue.

99FiveOh · Jun 6, 2011

toyman said:
I would pull codes to see if there is a lean condition or an O2 sensor issue.

chasenichols said:
Also pulled the codes and the only thing i got 172 (O2 fault/lean bank #1) for the KOER (key on engine running) test. KOEO passed and there was nothing stored.

toyman · Jun 6, 2011

What can I say. Somethings just need repeating.

chasenichols · Jun 7, 2011

So, i have been thinking about the tach reading and if it really bad or if it is accurate and reflecting the engine not operating correctly. To test this i got it up to speed on the freeway and down shifted to 3rd and let the car coast (no fuel or ignition inputs to make the engine run rough, just wheel input). The tach still did the same thing (fluttered). The engine felt like it was running smooth, so it must be a bad reading from the PIP.

I have beening thinking of testing the PIP signal...anyone know how? I was contemplating plugging an oscilloscope in to the signal wire. Anyone know which one it is?

Also, i am now concerned about the lean condition. Code says it is lean on bank one (is this the passenger side?). I wonder if these two things could be unrelated. What can cause a lean condition assuming my fuel pressure is good? Bad injector(s)?

I be sure to post the solution when i come to it, but in the mean time, thanks for helping my answer these questions guys.

99FiveOh · Jun 7, 2011

The tach sees the same signal the ignition system/computer sees. Engine stuttering, tach bouncing all over the place, it's pretty cut and dry at this point.

I have had an engine stutter caused by an O2 sensor before, but the tach never acted up on that occasion.

toyman · Jun 7, 2011

See if this diagram helps.

chasenichols · Jun 8, 2011

That should be a huge help, but the resolution on the pic is pretty bad...i cant read the text.

Any where else i can get a copy of that?

toyman · Jun 8, 2011

Here's a higher res picture. If you are interested I have the complete 1995 FORD car CD service manual. EVTM (Electrical and Vacuum Troubleshooting Manuals), Service Manual and PCED (Powertrain Control/Emissions Diagnosis Manuals). $20 to your door. PM me for details.

Use the "Ctrl" "+" keys to enlarge. The print is legible.

chasenichols · Jun 16, 2011

Finally got this problem solved and wanted to pass on what i learned.

I replaced the replaced PIP with the one from NAPA. (You're the man NOTA4.6!)

I didn't believe it the first time, so i replaced the ICM and the Coil, which didnt fix a thing. the only other option was the PIP so i went to Napa, paid the 70 bucks, and bought the good one. Problem solved.

The crazy parts was, i couldn't tell the difference between the two when i held them in my hand. They had the same everything all the way down to the same defects in the injection molded plastic. Totally the same, but totally different.

Conclusion:
O'reilly's = bad
Napa = good

At least when it comes to PIPs!

Thanks guys for your help!

99FiveOh · Jun 16, 2011

Glad you got it resolved! I know, I didn't believe it myself at first. How could so many "brand new" parts be malfunctioning? I fear that a HUGE run of these inexpensive PIP sensors has some kind of defect and needs to be recalled. Over the last few years I've read so many threads about people buying reman'd dizzies only to experience problems right out of the box.

So for anyone else to stumbles upon this post, do yourself a favor and buy an Echlin brand PIP sensor from NAPA and be done with it.

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