1996 gmc safari p0420 p0300 po131 p0151 p0172 decel misfire

I've replaced the EGR valve, all 4 O2 sensors, plugs, wires, cap&rotorX3. Now that I've got your curiosity - Here's our story - i've had this wonderful 213k mile 96 awd gmc safari(chevy astro) since 70k miles. Its only failings were 3 fuel pumps, 1 alternator, 1 radiator, one water valve thingy, a couple of window motors, and 2 starters. Then, at 200,000 miles I felt guilty and decided to tune it up :~( About 500 miles after it got new plugs/wires/cap&rotor (NAPA's best), it started misfiring - getting the p0300 code and the EGR pintle position code so I replaced the EGR valve. I forgot to mention that it almost always had the p0420 code - since 100k miles or so - it never hurt the performance or mileage. Along with the misfires, it lost power, mileage, and the effective use of the throttle above 1/4 throttle - much more and it bogs badly or shifts up/ revs and can't go any faster. After the EGR valve change that code stayed away but the p0300 kept coming back. the 131 and 151 codes started showing up at random so swapped each manifold O2 sensor. I've seen each of these codes again at least once. then changed the before and after cat o2 sensors today. Still gets p0420 and I'm sure I'll see p0300 again. (newest cap/rotor has brass contacts by the way)
Thanks in advance for any help!

I drove it last night with the doghouse off to check for ignition leakage -
looks great - with the doghouse off it sure is noisy! It almost seems that the trans may be slipping?? or the low power condition keeps the revs from getting high enough to shift under throttle? help!

Has the Cat ever been replaced? Did you install the AC/Delco plugs that the engine calls for? What's the fuel pressure @ KOEO, idle and any bleedoff?

These may be causes for your symptoms. A bad cat will throw the the P0420 code and possibly the random misfire code as well. Wrong (meaning aftermarket) plugs/ wires, cap and rotor will also throw the P0300 code. Poor fuel pressure will also throw alot of those codes as well.

What's the fuel trims saying as well as checking circuits/connections to the O2 sensors?

Good luck and keep us posted.

Has the Cat ever been replaced?

No, the Cat is still original @ 213kmiles - should I trust a local muffler shop to pick the right Cat or should I get it myself (if so is there a decently priced replacement? your recommendation?) The car is a lot louder than 100k ago. Could the muffler cause any of this?

- I noticed that the downstream O2 sensor was a little sooty - the other 3 looked pretty clean and identical.

Did you install the AC/Delco plugs that the engine calls for?

I can't remember for sure - they were expensive - got them at NAPA - I'm pretty sure I would have gone with Delco - the first set was still perfect @ 180K!

What's the fuel pressure @ KOEO, idle and any bleedoff?

I've got no fuel pressure gauge I guess I'd better deal with that. What's KOEO?
Might I need to swap the fuel filter? It might be original.. :-O

These may be causes for your symptoms. A bad cat will throw the the P0420 code and possibly the random misfire code as well. Wrong (meaning aftermarket) plugs/ wires, cap and rotor will also throw the P0300 code. Poor fuel pressure will also throw alot of those codes as well.

I didn't suspect the cat since I've had the P0420 for 100k miles.

The ignition parts currently installed are brass Accel cap/rotor and NAPA premium wires (fit perfect on the vortec, in the looms, on the plugs and cap. I've had a brass NAPA set of cap/rotor on it too. What do you suggest? What's the difference?

There is a LOT of green corrosion on the posts after just a few thousand miles - I cleaned the inside of the cap Saturday night - worried about carbon tracking - I've seen a lot of talk on the web about bad cap/rotors (dealer and aftermarket), talk about timing getting shoved out of whack because of knock sensor sensing other noises - possible software fixes for this - does the dealer have an upgrade for my 96 computer? I also saw one post about a severely worn distributor gear causing p0300 and many of my symptoms.

My latest fuel pump is probably @ 20k miles - it's noisier than the others (yes, I put the black tube blanket on it) and the engine seems to kick over longer before firing than in the good old days but idles perfectly once started.

What's the fuel trims saying as well as checking circuits/connections to the O2 sensors?

What do you mean by fuel trims? The cabling and plugs at the sensors are clean and corrosion free - not sure how to see anything else in that roomy engine compartment.

Today's commute (50 miles of hills) yielded the usual 420 and 300. I keep my reader plugged in and read on the fly/reset on the fly. This is never recommended in the books - they say to use the code reader with the engine off and the key on. Why not on the fly?

Thanks for all your help. I'll be glad to keep you posted and look forward to reporting THE fix!

If the cat has never been replaced, it's likely due...that's why you're getting the P0420 code. For a replacement, check price vs. warranty. If vehicle is louder than before, check muffler/exhaust system.

Visually inspecting O2s is not the best way (although it may indicate your P0172 code-Bank 1 Rich).

A lot of engines may throw a P0300 if the wrong plugs are installed.

Buy/borrow a fuel pressure gauge. KOEO = Key on, engine off. Replace the fuel filter...this may be cause of low fuel pressure (although still check fuel pressure) as well as your noisy fuel pump.

Normally, there are less problems with dealer ignition parts. For upgrades to the ECU (computer) check with the dealer. You'll need your VIN#. Worn dist. gear may be a cause but I would wait until the above is checked.

I take it that your code reader does just that...read codes. Or is it a scanner where you can monitor things like O2 sensors, TPS, etc. Fuel trims (STFT, LTFT) are the info the O2 sensors send back to the ECU to adjust the fuel entering the engine from the injectors.

Code readers only retrieve info (codes) stored in the ECU and cannot monitor things on the fly.

Hope this helps and keep us posted.

decel misfire and rich code sounds like egr or fuel pressure problem, intake gasket maybe as well come to think of it!

I've got a line on a fuel pressure gauge - may get some time to check it next week (mandatory overtime means the poor old car just gets the wheels driven off it this weekend!)

I'll buy a filter no matter what and get that installed (pressure check before and after just for curiosity's sake).

That decel missfire is very wierd - it happens consistently at a spot where I climb a long hill @55 mph then enter a freeway accelerating up to 65 or so, then the road levels and goes back slightly downhill - I have to get most of the way out of the throttle to keep from going faster- that's when it misfires the most - fairly violent bucking - maybe 20 chugs over a 1/4 mile or so, then the road levels and all is back to normal as I get back on the throttle(normal being no passing capability and poor mileage).

Regarding the EGR - I once had an 84 tbird with a tbi 302 that clogged its egr all the time. I eventually clamped a plate carved out of a tin can where the gasket goes - car was awesome forevermore. Will the obd II be upset with me if I try the same stunt to rule out my new egr valve as a problem? (temporarily, of course ;~)

Thanks again for your help!

Yes, my code reader is just that - got it cheap on ebay - I like it - it has a 6 foot cord that plugs into the obdII and has a big D connector (computer type) that plugs into the reader - I can leave it plugged into the patient and have the reader in a convenient location. Maybe someday I'll graduate to a scanner - I'll be reading your posts for recommendations! Thanks again.

blocking it off will lead to other codes and is illegal if left in but it will rule out the egr as a problem, there's a revised gasket with a screen in it to prevent the carbon from lodging the pintle open

12 thousand miles later I'd like to thank everyone for the help and apologize for this tardy update. No, she's not completely healed, but at 225,000 miles I'm not complaining much right now. I've done 2 things since my last post. Both were significant. First and foremost, when the car was so bad it would decelerate from 60 to 40 on steep hills, I made a permanent change from ARCO gas which I've used forever on all of my cars to CHEVRON. After 1 tankful this nearly healed the car. Yes, I retried ARCO and the car choked within 1/4 tank. I've always preached in favor of cheap gas but I can't do it with a straight face any more. I was still getting most of my codes but the Chevron allowed the car to maintain speed on hills. The other big thing I did was swap out the Catalytic convertor assembly. This basically healed it. I still get a P0300 every few days and I've had 2 each P0131 and P0151 but they stay away with a reset. I suspect that the old CAT combined with the 10% ethanol ARCO was the killer and maybe the new cat would do okay on the ARCO but I'm not trying that anytime soon. A new muffler and tailpipe are next on the list. I drove a 2001 awd astro with 48,000 miles yesterday - It had 25% more power so I know I'm not done yet but mine still flies down the freeway just fine. (also swapping out steering, shocks, and suspension parts). I'll let you know if the muffler makes any difference. Thanks again! (yeah, I know, I should change that fuel filter......o-:

You need to address you po131 and 151 dtc they can be a contributing factor to your intermittent po300 if they are in fact trying to tell you somehting is still not correct on your van. Yes a new conveter maybe giving you power and improved drivability back but if you don't fix everything that could have caused the conveter failure besides the fuel then you'll be replacing that one shortly. Po300 dtcs on thos pop up alot when a jobber dist cap is used. Don't know why just seen enough to know. As well fuel pump harness wiring go bad alot on those trucks and lead to repeatted and misdiagnosed fuel pump failures and problems. I always change that harness now when changing the pump.

You said that you replaced the O2s in March...Were they quality parts or the "fits all" kind? Have you inspected the wiring and connections lately?

Have you checked fuel pressure yet as well as intake leaks?

I suppose if the muffler is clogged enough it will affect driveability.

Keep us posted...better late than never.

HI ¡

Also be sure your ignition system is good. Check the ignition harness and wires of the distribuitor, are you having good ignition/timing ? you have to check your timing adjustments, if the timing is going bad it can produce missfires, check the CrankShaft position Sensor as well as the Cam Sensor... How many CKP and CAM sensors does it have ? does it only have one CKP sensor inside the distribuitor ?

She wouldn't start this morning so the top of the priority list says SAFARI.
I pulled the doghouse, installed the fuel pressure gauge, inspected and cleaned the cap and rotor (brass parts pretty green - brushed everything with a wire wheel and solvent/compressed air), switched the key on.

fuel pressure is about 60 for a couple of seconds then the pump switches off. It bleeds down to zero in less than 2 seconds.

She started, ran rough for a while. pressure stays around 50 when driving. After 10 minutes of driving it's running fairly smoothly. Checked the pressure again. Same quick bleed down from 60. The new fuel filter goes on today. (If I can find it o-: I should mention it had been parked for a few days on a hillside listing 15 degrees to port and was in heavy rain most of that time. That's why I checked the cap/rotor - there was no sign of moisture but maybe in the wiring somewhere else or in the air intake system.

Should the fuel pressure work like that? (Chilton doesn't mention it as far as I can tell)

also to answer some questions - new O2 sensors are borg warner with electrical plugs factory installed.

There's only one sensor in the distrubutor. They tell me the timing's not adjustable.

I haven't checked any other sensors but am still mighty suspicious of that egr valve - the surgeon general says we shouldn't breathe in smoke and I don't think it's good for my little vortec either! (I haven't tried running it unplugged or blocked off)

I'll do some intake leak checking w/ether now that the doghouse is off.

Thanks!

Up to almost 228,000 miles now - the new fuel filter was the silver bullet (almost) HUGE change resulted - the thing must have a check valve built in - the new one did not bleed down fast like the old one. I've been working on suspension issues lately - Moog idlers are a must and Monroe coil overs in the back really jacked it up. I STILL have p0300 most of the time and now p0131 again. The car misses more when cold but is strong enough to drive away from my friend's 2005 v6 mustang (~; Did you know that the first 6 inches of exhaust pipe after the manifolds get bright red hot in you drive fast uphill for 10 minutes? (found that out driving to work in the dark with the doghouse off) - I said to myself "there's a red light under the car! What's that? Well she's not likely to get any more love for a while - It's snowing and I need my AWD! Just thought I'd update - Thanks for the help everybody! Change your fuel filter and don't use cheap gas!