Hello everyone. New member here seeking help with this problem. I've read many of the other threads and tried numerous things to no avail.

So driving one day and the truck starts bucking and loses a lot of power. Wouldn't let me maintain but 50-55 mph. I thought fuel filter or pump but after reading some threads on here I do some testing of sensors and coil pack. Coil pack showed that bank 3 is going bad, tps and maf tested fine. I've cleaned the iac and maf. It runs pretty good with maf unplugged but as I've learned here that's because the computer is in limp or open loop mode. My thoughts are that it's not fuel related because it runs pretty good with maf unplugged. Please help.

99 3.0 5 speed 2wd nonflex fuel.

 

Is the Check Engine Light (CEL) on? Have you scanned the ECM with an OBDII reader for codes?

 

I have not but plan on doing this afternoon. No check engine light but bulb maybe blown

 

CEL should com on with key on, and then go off after engine starts to turn(cranking)
If it doesn't come on with key ON then yes, bulb is bad

 

definitely blown then. I'm otw to have the codes read now. Stay tuned.

 

So this is the codes it's was showing.
P0401 egr flow insufficient
P0402 egr flow excessive
P0102 maf circuit low (probably because it's been unplugged though I did plug it up for the codes to e read
P0420 catalytic deficiency bank 1

 

You can get OBD2 code reader for $10-$15 called ELM327

Can you drive at highway speeds or does it feel limited?

P0420 could mean exhaust is partially blocked so limited air flow out which also causes "bucking" and limited top speed

P0401 and P0402 can means EGR valve is sticking so might be time to clean it or change it
Too much exhaust(P0402) will certainly cause running issues
P0401 will cause pinging noises when accelerating

 

I was thinking new egr valve, pcv just because it needs it, seafoam it, and see what happens. I've got to replace the coil packs too. The 3rd bank reads almost no resistance at all. I think it was.8 ohms. It hasn't failed yet because there's no miss with the maf unplugged but I'm sure it doesn't have long.
If it still has issues I'll start checking the cats.

Thanks for your help. I'll post whatever outcome.

 

Coil packs ohms should be 0.7 to 1.4 ohms, but all 3 should be close to the same in a 3 coil pack

 

Yeah the other 2 were like 1.8 or 1.9. The fuel filter looks original so I may change that a well and run injector cleaner. Any suggestions on which one?

 

Might check O2 sensors as well, think the 99 has 3? It could be either a sensor going bad, or a clogged catalytic converter, or both.

 

I was finally able to get the egr valve today and put it on. No improvement. Clogged converters? And will the o2 sensor cause it to do the hucklebuck 2 step? Thanks for everything so far.

 

Make sure the EGR vacuum regulator is working and connections are good. Might as well check all your vacuum lines for cracks while you're at it. Check the air cleaner duct work for cracks. If the O2's are wore out, they can throw the whole system off... they can send the computer inaccurate values. Most of the time if you get an O2 code, it's due to the fact it's not working at all.

 

So I went ahead and replaced the o2 sensor on the side that threw the code. No change. So doing more research and thinking the cam syncro maybe? My thoughts are that if the cats were clogged that it wouldn't lose the jerking with the maf unplugged. Correct me if I'm wrong. Sorry about being so long between posts but I'm only able to get a part or 2 each week. Thanks.

 

Anyone???

 

I'd check for exhaust back pressure next. Can be done with a vacuum guage. They aren't expensive at harbor freight or rent one from an auto parts store. Rev engine to 2k rpms and watch to see if vacuum pressure starts dropping. Vids on YouTube how to do this. If cat is clogged you'll lose vacuum as engine is revved up

 

OK I just did the test with vacuum gauge to see if converters are clogged and apparently it isn't. Vacuum on the gauge went up to 60" and stayed there without fluctuations. Should I replace the cam synchronizer? HELP! LOL

 

I also wanna add that with the maf plugged in it still runs like crap before it gets warmed up.

 

Idle vacuum should be 17"-21"

If you raise RPMs to about 2,500 and hold it there, vacuum should drop a bit then come back up close to idle levels
If vacuum is slowly dropping as you hold higher RPMs you have clogged exhaust

60" of vacuum would be Outer Space

 

It's dropping a bit but it stays there. It doesn't go back to idle reading.

 

What kind of vacuum gauge are you using ?

30" is regarded as the maximum vacuum level available at sea level, so there is no reason for anyone to make a gauge that will will measure more than 30"

 

I'm sure that I'm wrong about the actual reading. The guage is at home so I'll check but at idle it was in the green and upon revving it upto around 2500 rpm it dropped and stayed.