2000 GMC Jimmy sputtering problem

[Rick Norwood]

2000 GMC Jimmy 2wd 4.3L I have a very annoying problem that I can't seem to find. In the morning when the truck is cold, it is the most obvious. I start the Truck and it idles fine, perfect, no problems. When I start to take of and accelerate up to speed, it starts to sputter a little bit. Not real bad just enough to make you back off of the gas. It settles down and then I can usually give it more gas and take off. When the truck warms up it is still there, but hardly noticible. It threw a P0300 Random Misfire code once, I cleared it, and never threw another code again. I replaced the Thermostat because the dash gage seemed to be slightly cold. I also replaced the Cold Air Temp Sensor in the intake duct, cleaned the MAF Sensor, and replaced the air filter. I replaced the coolant temperature sensor too. The plugs are approximately a year old and the wires, cap, and rotor are 6 months old. Fuel Filter is brand new. Nothing has helped.

[old_master]

Rick, no mention of fuel pressure, have you checked it?

[Rick Norwood]

Originally Posted by old_master

Rick, no mention of fuel pressure, have you checked it?

No, I haven't checked it yet. It will take me a couple of days to get to it.

[Rick Norwood]

Well here is a happy ending and another problem put to bed thanks to Old Master. A million thanks OM.

To make another long story short. My problem was a bad distributor cap. I replaced my Rotor, Cap, and Wires on May 11, 2009 with Autozone Duralast Cap, Rotor and Wires. I spent approximately $105 USD replacing the original stock Rotor, Cap and Wires that were over 9 years old and had 130K miles.

That is where my problem started.

Sometime around November 2009, I started noticing the symptoms described in the first post. The problems got progressively worse until last week when I could not drive more than 2 miles without throwing a P0300 Random Misfire code. As soon as I erased the code with the scan tool, it came right back on. The sputtering turned into bucking, fuel consumption was up, and the truck simply ran like crap. I finally had to park it for a few days, afraid to drive it for fear it would leave me stranded.

In a PM, Old Master told me that P0300 codes almost always come from the secondary ignition circuit, meaning plugs, wires, dist. cap, rotor or Ignition coil. He also reminded how picky these vehicles are about the brand names of parts, and how AC Delco parts are the only way to go on Secondary Ignition components as the Aftermarket products simply won't hold up.

To cut to the chase, yesterday, Jan 26, 2010, I replaced my AutoZone Duralast Distibutor Cap and Rotor with an AC Delco Cap and Rotor. I did not replace the wires. The results were unbelievable. No more sputtering, no bucking, no jerking, no more SES light, just smooth idle and acceleration. Problem solved.

I have read on this forum for years about OEM parts vs. Aftermarket parts. I am now a full fledged flag waving proponent of AC Delco Parts. This is not to say that they don't let a bad one slip through once in while. But here is the lesson learned. The original OEM cap that I replaced lasted over 9 years, the aftermarket cap from AutoZone lasted less than 6 months before the symptoms started. You do the math.

Luckily I got off cheap, the new AC Delco cap and rotor only cost me $53 USD, which is within a dollar or two of the price of the AutoZone cap and rotor. The part that amazes me the most is that I had to go to 3 different part stores to find an AC Delco Cap, and even then they had to order it from the warehouse.

Every Parts store claimed that their parts were equal to or even better than AC Delco, and that is why they pushed their own brand. DON'T BE FOOLED! Stick to your guns and insist on AC Delco. The price is not that much different and you'll be better off in the long run.

[Rick Norwood]

I saved the bad cap and I tested it with my Ohm meter and could not find anything wrong. I would love to find a defect, does anyone know a good bench test?

[BOBWIRE67]

I have same problem been working on it a week!! and just now relized I to installed auto zone cap and rotor Im going right now and replace with AC DELCO AND i WILL POST THE RESULTS THIS EVENING! warning to Auto zone Im on my way! lol

[old_master]

Very important to put a dab of silicone dielectric grease on each terminal, inside and out, of the cap, also on the rotor center and on the tip.

[fj4072]

Bringing this problem alive again...I have this same problem EXACTLY. This is the only place I've found on the web with the same problem as me. I'm a little confused on why it would be the cap when it's temperature related? I have replaced cap (yes autozone brand), rotor, wires, AC Delco Plugs, coil, crank position sensor, fuel filter, TPS, cleaned my MAF too. I too have pulled the P0300 1 time, shop replaced crank shaft position sensor, but still have the same problems. I've even blasted it with Seafoam, no change. Here I am thinking it's the injectors or fuel pressure problem until I read this, but doesn't make sense. UNLESS it has to do with early morning moisture??? Maybe. I will replace my cap with AC Delco and report back. Hope this makes 2 of us with the same outcome of just a darn cap.

[old_master]

Post #4 explains it. Not exactly sure what causes it, could be a design flaw in the cap, could be inferior materials were used when manufacturing the cap, could be poor insulation of the "runners" in the cap. If you look at the cap, you'll see that the plug wires are not attached to the cap in the firing order of the engine. This was done in an effort to eliminate crossfire inside the cap, (which will cause P0300). If the insulation is inferior, crossfire will occur. If you check around the forum, (not only this one) you'll find more than just a few instances of AZ caps, and other aftermarket caps, causing problems. AZ by far is the worst offender though Sometimes they work for a day or two, sometimes they last a few months, and sometimes they fail right out of the box.

[Rick Norwood]

Originally Posted by fj4072

Bringing this problem alive again...I have this same problem EXACTLY. This is the only place I've found on the web with the same problem as me. I'm a little confused on why it would be the cap when it's temperature related? I have replaced cap (yes autozone brand), rotor, wires, AC Delco Plugs, coil, crank position sensor, fuel filter, TPS, cleaned my MAF too. I too have pulled the P0300 1 time, shop replaced crank shaft position sensor, but still have the same problems. I've even blasted it with Seafoam, no change. Here I am thinking it's the injectors or fuel pressure problem until I read this, but doesn't make sense. UNLESS it has to do with early morning moisture??? Maybe. I will replace my cap with AC Delco and report back. Hope this makes 2 of us with the same outcome of just a darn cap.

You will chase the problem all around the secondary ignition circuit, ENDLESSLY, replacing all sorts of stuff, not to mention pulling your hair out and loosing sleep. Your problem will only get worse unil you scrap the aftermarket junk and install an AC-Delco cap. Old Master made a believer out of me. Listen to him and learn. AC-Delco is the ONLY F@$&^$#*&ing cap to use.

[Rick Norwood]

Originally Posted by old_master

AZ by far is the worst offender though Sometimes they work for a day or two, sometimes they last a few months, and sometimes they fail right out of the box.

I thought so too until I replaced the entire Distributor on My 2001 S10 Blazer. I found out after the fact that is was an Airtex Distributor that came with a Cap. Within 6 months, the Airtex Cap burned through on the inside and shorted out between the two neighboring wires. So add Airtex to the list of garbage Caps. AC-Delco is the only way to go.

[Rick Norwood]

Just as a follow up, Jan, 2014 will be 4 years since I replaced the AutoZone cap with the AC-Delco cap. I now have over 50K miles on the new AC-Delco Cap WITH NO CODES OR ISSUES. None of the aftermarket caps that I have tried lasted over 6 months.

[fj4072]

Originally Posted by old_master

Post #4 explains it. Not exactly sure what causes it, could be a design flaw in the cap, could be inferior materials were used when manufacturing the cap, could be poor insulation of the "runners" in the cap. If you look at the cap, you'll see that the plug wires are not attached to the cap in the firing order of the engine. This was done in an effort to eliminate crossfire inside the cap, (which will cause P0300). If the insulation is inferior, crossfire will occur. If you check around the forum, (not only this one) you'll find more than just a few instances of AZ caps, and other aftermarket caps, causing problems. AZ by far is the worst offender though Sometimes they work for a day or two, sometimes they last a few months, and sometimes they fail right out of the box.

Got the AC Delco Cap and Rotor from Rockauto, installed it, problem gone! Thanks a bunch to all! Evidently previous owner broke the plastic part on the distributor that you screw into, just the threaded pre-formed holes. Do they sell this part separately, instead of buying a new distributor? I may have to JB Weld a nut there on the distributor. I have 3/4 circle there, so it's tight, but I don't like this. Now, I'm going to get my money back at Autozone. Happy Happy Happy.

[Rick Norwood]

Originally Posted by fj4072

Got the AC Delco Cap and Rotor from Rockauto, installed it, problem gone! Thanks a bunch to all! Evidently previous owner broke the plastic part on the distributor that you screw into, just the threaded pre-formed holes. Do they sell this part separately, instead of buying a new distributor? I may have to JB Weld a nut there on the distributor. I have 3/4 circle there, so it's tight, but I don't like this. Now, I'm going to get my money back at Autozone. Happy Happy Happy.

If Autozone refunds your money I'll be shocked. When I tried to get my money back, they laughed me out of the building with a resounding "HELL NO". Glad to hear you're up and running.

[old_master]

With the broken ear on the distributor... You can try repairing it, and if it doesn't work, get a distributor that has an aluminum housing, not plastic. Skip White Performance usually has them in stock, part #6671-BK, or at their Ebay store, for around $42. Great price, great part.