Hello all,
This is my first post here! I have looked to see if the codes have been posted in a previous thread, can not locate.
I have just bought a 95 Jimmy SLT 6cy. Heavy on the miles but a rebuilt motor with only 60000 kms.
Running a little rough. Read the codes and have come up with
P0300 - Random/Multiple misfire detected and
P1406 - Manufacture controlled auxiliary emission controls

looking for some ideas for the home repair.
some of the recent work done b-4 purchased:
spider fuel rail
O2 sensor - replaced a couple of times (probally because of the misfire)
Fuel pump
tune up - plugs and wires
Need some help
Thanks in advance

Welcome to the forum!
P0300 usually indicates a problem in secondary ignition such as distributor cap, rotor, ignition coil, spark plug wires or spark plugs. The P1406 indicates a problem with EGR pintle position, possibly a piece of carbon stuck in the valve not allowing it to close completely. Keep in mind the DTC's don't mean replace the part, it means those are areas to check for problems. Post back with your results.

Thanks for the quick response.
Do think that one code has to do with the other?

I just looked on the on line and found somemore info:
A code P0300 may mean that one or more of the following has happened:

<Faulty spark plugs (http://www.obd-codes.com/trouble_codes/generic/p0300-random-multiple-cylinder-misfire-detected.php#) or wires
Faulty coil (pack)
Faulty oxygen sensor(s)
Faulty fuel injector (http://www.obd-codes.com/trouble_codes/generic/p0300-random-multiple-cylinder-misfire-detected.php#)(s) <
Burned exhaust valve (http://www.obd-codes.com/trouble_codes/generic/p0300-random-multiple-cylinder-misfire-detected.php#)
Faulty catalytic converter (http://www.obd-codes.com/trouble_codes/generic/p0300-random-multiple-cylinder-misfire-detected.php#)(s)
Stuck/blocked EGR valve (http://www.obd-codes.com/trouble_codes/generic/p0300-random-multiple-cylinder-misfire-detected.php#) / passages
Faulty camshaft position sensor
Defective computerAgain just wondering if I look at the EGR - clean or replace might that solve both codes?
Or the codes are unreated?

Thanks Again also appreciate the comments and suggestions.

When troubleshooting DTC's, always start with the first one. If the EGR valve doesn't close completely, it can cause stalling and/or rough running. Usually when only those two DTC's show up together, the P1406 will be listed first. You might try removing the EGR valve and inspect for carbon on the pintle and clean it if necessary. Then continue with the P0300 troubleshooting.

Well I'm back again.
Was able with your help fix the P1406 code. The EGR was unplugged. Erased the codes and tested again.
P0300 keeps coming up - random miss fire - which is a difficult code as there is many variables.
Symtoms - very very very poor gas milage - runs kinda? ok at steady low speeds with no inclines - still burbs a bit.
At highway speeds and hills burbs spits chugs etc.
spoke with previous owner and recently has changed the fuel pump - fuel filter - and spider to the injectors.
At this point I need a vehicle badly as the motor on my grad prix 3.1L blew the bottom end after replacing the head gasket about 6 months ago.
So any suggetions would be interesting, but note I had to take the Jimmy to the doctor for a hopeful fix to be on the road again soon.

when was the last time the cap,rotor,plugs, and wires were changed? thats where id start.

Some more history. Looks like previous owner kinda sucked me in.
they have changed the following very recently:
cap/rotor plugs
catilac convertor
fuel pump/filter
injector spider
coil on engine
tried used distribtor
my mechanic is stilling having troubles pinpointing the cause.
It seems to run crappier as it warms up and is drinking the gas.
it also is running very rich as per the scope.
The meter is running $$$$$$$$$$$$$$$$
help!!!

Sorry the 2 o2 censors seem to be working fine

If it is still throwing a miss fire code you need to look for miss fire.
Can you short out plugs and find the miss?
Which engine and engine code and VCM or PCM?
Flat top dist with wires out the side or out the top?
Does your mechanic have a engine capable scanner to check for which cylinder is doing the miss fire?
What kind of spark plugs are you using?

The Dist. is a flat top.
The mechanic was highly reccommended as the doctor that can find the cure. He has scoped it several times and can not pinpiont one cylinder in paticular. The fuel he says is reading rich. He claims the plugs are good but I'm beginning to wonder? The type of plug is AC delco. I have not been in contact with the mech. in the last 2 days for the gut wrenching fear of the unknown and the cost attached??????
Unsure which engine type and or code typre how can I tell. My MAC code reader is calling up P0300. Once I cleared the codes it comes back up with in minutes of driving.
sorry for my lack of knowledge of VCM or PCM.
please respond need my wheels back

Running rich and a miss fire code you need to find someone with a good engine capable scanner to get in there and see what is going on.
Also a good fuel pressure test would be in order.
Good luck MT.

I see alot of tune-up and scanning, but has anybody tried a compression test on the cyclinders ?

Still at the shop. but good call on the compression test. I will speak to the mechanic.
He at this point believes it is the computer mounted on top of the wheel well.
Still keeping my fingers crossed.

The Dist. is a flat top.
The mechanic was highly reccommended as the doctor that can find the cure. He has scoped it several times and can not pinpiont one cylinder in paticular. The fuel he says is reading rich. He claims the plugs are good but I'm beginning to wonder? The type of plug is AC delco. I have not been in contact with the mech. in the last 2 days for the gut wrenching fear of the unknown and the cost attached??????
Unsure which engine type and or code typre how can I tell. My MAC code reader is calling up P0300. Once I cleared the codes it comes back up with in minutes of driving.
sorry for my lack of knowledge of VCM or PCM.
please respond need my wheels back
hey there,
II have the similar problems as u do. my husband changed the catylitic as it was plugged so that might help u. let me know what the "doc" has to say...thanks code 300