Hi, I was hoping you guys may be able to help me out with my latest problem... I've posted on another website, but I'm not really getting anywhere. So here we go..

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I've been having this problem on my 92 940 for some time and its slowly getting more frequent. It starts and runs great, but it gets this fit where the tach needle jumps around and it runs like crap.. then quits. It's a REAL PITA to get started again, and when it does, you have to hold the pedal to the floor to keep it just chugging. Then once it runs and you rev it for a while, you have to two-foot the gas to get it home. Go into boost and it really starts to freak... It may or may not immediately restart, but the next morning it usually fires right up. The only warning you have is when the tach starts twitching.. then get ready for the fun.

The cluster was replaced three times, the coil is new, the wires are good, as well as the plugs. It's got alot of miles on it, but there is no really visible signs of rotted wires or missing connectors. Engine harness looks fine.. no rot.. I will be swapping over to Mega Squirt 3 here soon, figuring the totally isolated, stand alone fuel and ignition system may bypass any hidden LH 2.4/dash wiring harness issues.

Any ideas or should I just not bother and go for MS3?


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A crank position sensor was suggested by forum reply..
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Just replaced the crank position sensor today... It did not help...

The CPS did nothing to improve anything. Now as I turn the key to begin to start it, the tach jumps and sometimes the speedo jumps around. This is the third dash cluster in it and nothing helps. I had it running and the tach started going crazy, swinging up steady to 6000, then the wideband dropped to 10 and the engine quit. The wideband drops with the tachometer rising, I guess getting a signal to dump more fuel based on tach reading.

Also, strangely... the interior key warning/chime warbles a little too... not a steady chime but a wavering warble as well.. Something electrical... I don't know where to start looking really. What would cause such wild tach jumping? The car runs like crap and stutters and hesitates and generally is really beginning to **** me off.. LOL.

I'm hoping stand alone mega squirt 3 will bypass this nightmare... So I think the 70 dollar CPS is going back for a "refund"...

Any ideas for a simple fix would be great, until I can get all the LH stuff removed and the MS3 harness installed... It's going to be a big job...

Thanks,
Mike

 

"The cluster was replaced three times"?!

You better first stop, whether someone is selling you things or you are hyper swapping.
And, no I wouldn't be doing an MS3 harness, whatever that is.

Any codes? MAFS OK? Any air leaks in the turbo plumbing?
A "wild tach" corresponds to the RPMs or just the tach going high?
What "white band"?

 

a megasquirt will need to connect to all the same sensors, and will just replace the ECU and ICU with your own tweakable programming. lots and lots of opportunities to get it a ltitle or a lot wrong. too lean, you blow holes in your pistons and get to start all over. too rich, and your fuel economy sucks and your cat clogs up.

the jumping tach combined with the misfiring probably does indicate something funky with your ignition as its connected to the output of the powermodule that drives the coil.

your total shutdown when you get on boost suggests a major air leak somewhere between the MAF and the engine intake manifold. I was having issues on my 92 turbo with the silicone rubber hose that goes from the MAF to the turbo intake side, at high airflow, the turbo was sucking the bottom side of that rubber tube 'in', and allowing air to bypass the MAF, resulting in too lean of a mixture. the rubber tube was oil soaked from my aging turbo, replacing it solved the problem permanently (I got by a year by reclampin git 2-3 times before I gave up and replaced it).

the engine rotation is detected by the CPS, this goes to the ICU and is used for spark timing. the ICU forwards this timing signal to the ECU, which uses it for fuel injection timing. the spark timing is determined by, primarily, the RPM and engine coolant temperature. the fuel injection timing is determined by the RPM, and the fuel amount (pulse width) is determined by the RPM, MAF, engine coolant temp. The o2 sensor provides a fine trim to maintain the right stoichiometric mixture.

there's other inputs, but these are the most important.