new LPM program, same old pinging

[JustinSchick]

Posted this to the SHOTimes lists but thought I'd try here too:

Greetings all,

The saga continues with my ping happy 92. It seems to only be happy (most of the time) with the stock MAF and no chip. It will only ping like that after it's heat soaked and under a heavy load, and only very slightly. 99% of the time it does ok. After a couple of re-burns I was convinced the pinging with the 80mm / LPM setup was a bad MAF. I sent it off to be calibrated and sent my chip back to Ted for his base, generic program set. I got the LPM back today and installed it over lunch time with the stock MAF. Once warm, I found the pinging is still there. It occurs just beyond idle RPMs and under 3k RPM, at throttle positions between say 1/4 and just before WOT. It pings BADLY. Same symptoms as the old 80mm / LPM combo, except this is the stock MAF and the LPM is programmed accordingly.

I am looking for recommendations about what to look at next. I am convinced it's not the MAFs or the LPM. I replaced most all sensors during the shortblock swap almost 20k ago. I don't remember doing the manifold pressure sensor (BAP), but am now wondering if MTX cars even use one. I also want to look at the sensor that ties into the MAF voltage and sucks it away as it starts to fail. One of the Don's posted the part number a while back, and I think it had to do with the secondary actuators. I believe Ransom was the first to run across this (publically anyway). Also, if anyone could post the procedure I want to check the voltage output of my TPS. Is there anything else I should consider?

Thanks in advance,

Justin Schick

 

[sdpatt]

The BAP sensor is the barometric absolute pressure sensor and measures the pressure of the atmosphere, not the intake manifold. And yes, the MTX needs this input too to determine the mass of the oxygen in the intake air charge.

Have you replaced your knock sensor? Without that input, your EEC is blind to the racket.

 

[luigisho]

I'm wondering if the lpm isn't accentuating a problem that was already there. How fresh are plugs/wires? When was the last time you checked their gap? Do you run high octaine gas? Is the computer one which has a history of difficulties with the lpms? Knock sensor is also a great suggestion.

 

[clintonk]

Any EEC codes? My '90 threw a code for no knock sensor signal. I replaced the knock sensor, and all the pinging stopped.

Clinton Knight
'90 White 182K
'95 Green 50K

 

[JustinSchick]

Thanks for the replies guys.

Most all of the sensors etc. were replaced almost 20k ago during the installation of a new shortblock. That includes plugs, but I did not do the knock sensor. No codes at all and it sails through the KOEO and KOER tests just fine. Could the knock sensor be dead without the computer realizing it?

I have to try pretty hard but I can make it ping with the stock MAF and no LPM. So I think the LPM etc. are sound and just bringing the problem to the forefront.

The computer itself has always had a sloppy connection with the 60 pin connector. I gave up trying to get the connector off to clean the pins, as the bolt just spins. Ted suggested trying a new one, so I'm now debating wether to go j-yard diving or just buy a new one outright. Thoughts?

 

[luigisho]

Being cheap I would go for a used computer from a year that has been known to work. I swapped in a '91 computer because the ones in the '90 were known to be problematic. Shop around. This may or may not cure your pinging. If you get another it's much easier to install w/someone's help to keep centered and provide stability when hooking it back up. Change the knock sensor too. Couldn't hurt.

 

[hanshua]

Just to be sure its not something dumb... you are using preium gas right?

The LPM advances timing, requiring you to use a higher octane gas....

 

[JustinSchick]

I think I'm gonna start calling the local j-yards for leads on an ECM. I wish I knew a local SHOwner with a perfectly running X2J setup I could swap parts with...

I run nothing but Texaco 91 octane. The only higher I've seen is 92 at Amoco stations. Is there anything better to be found in the KC area?

Did the LPM swaperoo again today. Drove to work with it and got the pinging again, took it out over lunch and it was fine. Well, by fine I mean I could hear a very faint "snap-snap" 1 out of 5 tries, just for a second, then it went away. Makes me think the knock sensor is doing his job, and sounds much better than the "SNAP-CRACKLE-POP-BZZZZZ" that happens constantly with the LPM in.

I really think I'm on the bubble with the stock setup and just get pushed over the proverbial edge with the LPM in. I'm going to try a de-carbon session this weekend and start trying to pin down a faulty sensor one by one.

 

[Prophet78]

This was brought up before by a member who had teh same problem. He was thinking it was the LPM Maf combo and turned out to be a simple reset of the computer.

Try Ted's directions on how to reset the computer and have it "learn" a new load with the MAF and LPM in. It fixed his problem, maybe it is yours.

-Jeremy-

 

[JustinSchick]

I wish it were that simple...

I reset the ECM every time I un/re plug the LPM. I normally follow Ted's instructions of simply unplugging the ECM's ground connector located next to the battery. Last night for grins I tried the "******** reset" mentioned by some of unhooking the battery's ground entirely, and stomping on the brakes for 30 seconds to drain any residual voltage. After doing so I let it sit unhooked overnight, stomped the brakes again this morning for good measure, reconnected everything and had the same problem with the LPM during the drive into work.

John Hrinsin posted a "super duper ******** reset" to the SHOTimes lists, which I have not tried yet. I don't expect any different results but what the ****. He suggested unhooking both battery cables and touching them together for a minute or so, to completely drain any residual power from the ECM's capacitor. I will try this over the weekend during my de-carbon process, oil change, etc.