Poor running 1990 under load
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Joined: Jul 2009
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From: Beach ND
Poor running 1990 under load
My car starts great and idles great. The more you run it and it warms up it seems to run poorer, stumbling, hesitation. Then when you go wide open throttle, it shifts down and runs like it has a governor on it. It seems to have a fuel shortage. It will go up to 3500-4000 and just act like it is starving for fuel. No increase in speed. Just shutting down. At idle it will rev up fine. This happens under load. I have replaced the injectors with Bosch. I have checked the fuel pressure at the rail and under load it still read over 40 lbs. When this is happening it will throw a code 44. I have replaced the 02 sensor, the CTS. the MAP sensor. I have also checked the EGR valve. The diaphram will move with a vacuum applied and will hold vacuum. I am wondering if it might be the ECM? Any thoughts?
Thanks,
Don
Thanks,
Don
Safety Car
Joined: Apr 2011
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it might be as simple as a bad sock in the tank or filter. 40 psi at idle is nice. does the pump hold 40 at 3000 rpm? or is it struggling to keep 20 psi at that speed?
Cats are another consideration if you say it just has no power or it won;t rev...The statement of"it shuts down" is confusing. Does that mean it turns off? shut down? or simply won;t rev? hits its wall and cannot go any further?
test the fuel pressure at sustained rpm and you will likely find a slow pump.
Cats are another consideration if you say it just has no power or it won;t rev...The statement of"it shuts down" is confusing. Does that mean it turns off? shut down? or simply won;t rev? hits its wall and cannot go any further?
test the fuel pressure at sustained rpm and you will likely find a slow pump.
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From: Beach ND
Thanks for the reply. I forgot to say that a new pump and filter have been put in. It hold the 40+ pounds of pressure at the 3500 or so rpm. I checked with a guage. Sorry for the confusion. I mean it hits a wall and won't rev any further. When it is in neutral and not under load, it will rev fine.
Thanks, Don
Thanks, Don
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From: Beach ND
I got to thinking about the cats and checked the exhaust coming out the tail pipes. There didn't seem to be much. Loosened the head pipes at the manifolds and it made a world of difference. I had a friend knock out the inside of the main cat and it seemed to be much improved. It revs up fine at idle and also under load and will now upshift properly after being floored. I didn't replace or clean out the 2 precats in front because it seems to run okay. Should these be cleaned out or replaced anyway?
Thanks for the great suggestions. I am a happy man.
Don
Thanks for the great suggestions. I am a happy man.
Don
Melting Slicks
Joined: Sep 2008
Posts: 2,376
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From: Cherokee National Forest TN
There is a replacement head pipe available without pre cats from our after market suppliers.
Some have had a shop remove the pre cats & install tubing.
Since I'm a cheap b-tasd, for my 90 I whiz-wheeled the pre cats open from the bottom, broke the media out, fabbed cover plates & welded them in place.
Butt - o - meter says performance has been enhanced.
Some have had a shop remove the pre cats & install tubing.
Since I'm a cheap b-tasd, for my 90 I whiz-wheeled the pre cats open from the bottom, broke the media out, fabbed cover plates & welded them in place.
Butt - o - meter says performance has been enhanced.
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Joined: Jul 2009
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From: Beach ND
Just another update. I replaced the header pipe with one w/o the precats and I also put on a new back cat. It runs great now. I have been putting up with this problem for some time and you guy diagnosed it quickly and accurately. You all have my deep appreciation.
Again, thanks,
Don
Again, thanks,
Don
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From: Beach ND
I don't remember for sure where I got mine. But it might have been off of EBay. I see they still have several choices for Y pipes with and w/o front cats. I'm sure the major exhaust suppliers have them for sale. I'm sure not legal in California and maybe other places. There is no emissions check here in ND.