Hello,

I've spent about two hours searching this site and others and still just as confused:

The car has an intermittent "will not idle after warm up". Been around for a few months.

It almost always starts good cold (it has a few times had the issue from a cold start, although rare). Drive it a few minutes, idles fine, cut the engine off for a few minutes, start it and it is difficult to start and will not idle. Using both feet gas/brake action you can get it to move and it does well accelerating and cruising. This happens about 40% of the time. Some times you can go days and it will run fine; although it does appear to be getting more frequent.

For example, last Saturday the Blazer was started after sitting a few days.
It started fine and was driven 20 miles and as I stopped to get gas it idled fine at the pump. Got the fuel, paid, etc (5 minutes) and it was difficult to start, had to use both feet to get it on the interstate and it did fine the next 60 miles at 70 MPH. When I got to the exit after this drive it died at the stop sign and I had to do the two feet thing to get it going again, it died (or I did the two feet thing) at the next 4-5 stops over 10 miles to my destination. I let it sit about 10 minutes, and it started and idled fine.

I get one consistent code: P0304 (4th cylinder miss). I have replaced all plugs and wires, did not help/stop code from reappearing.

My search seems to point at the spider injector and/or the ignition control.

Both of these are rather costly and I don't won't to throw money at it and it not be it. We bought the Blazer 4.5 years ago with 65K. Vehicle now has 195K and none of the two things above have been addressed since we've owned it.

What are your thoughts per my description above?

Thanks in advance!

 

Did you replace the cap and rotor with the plugs/wires? Check the play in the distributor shaft as well. Might be time for a new distributor....get an aluminum one..about $50.

Other things to check is the fuel pressure; do the leak-down test too. Could easily be as you suspect or an intermittent fuel pump, dirty fuel filter, corroided electrical connection to the fuel pump....etc.

Good luck with your search.

 

Be lucky you don't have the dreaded p0300 code!

Anyway, your cylinder misfire is narrowed down to #4. I doubt highly that a weak fuel pump would cause a one cylinder misfire. Not even a lazy/leaking Fuel Pressure Regulator. More than likely, those cause the p0300 codes, or just a rough idle, no start condition. It however doesn't hurt to check the Fuel Pressure and leak down anyway.

Life is much easier if you have access to a scanner that does live data. You can get them at harbor freight for a decent price. In case you don't have a scanner like this, or cant not easily source one, I will give you two ways to diagnose this;

With Scanner:

Under live data, take a look at the STFT1 (Short Term Fuel Trim) and STFT2 (bank 1 and bank 2 respectively).

Under idle when the car has went into closed loop watch these values. If the numbers are positive or negative more than 5% you have an issue.

Positive STFT means the engine is running lean, not enough gas, or too much air. This could be from a vacuum leak, misfire in the ignition system, or fuel problems. Excessive positive STFT on both banks normally lean towards a vacuum leak. Let us narrow it down to either fuel or igntion or vacuum leak;

Hold the throttle in park at 2000 rpm's while looking at this value of STFT. If the values start to drop, then you are looking at a vacuum leak. As the engine RPMs increase a vacuum leak becomes less effective on the engine performance. If your numbers do not drop at all or very little then you are dealing with a fuel delivery issue. In my experience, once a fuel pressure test and leak down test is done, and numbers are good, you are looking at a faulty or clogged injector.

Negative STFT is when the truck is running to rich, i.e. too much fuel, not enough air. This could be from bad ignition components, to engine mechanical issues like a bent valve, leaky injector, cracked head, too much fuel pressure, etc.


Without Scanner:

Obviously this method is not as accurate as using a scanner, but you can get an idea of where to look.

On cylinder number 4 (middle cylinder on passenger side of motor, while the engine is running, carefully use a spark plug wire puller, and pull the wire off the cap. Be extra careful here as you can get a bad electrical shock that will send you into another world. Make sure you are grounded. If there is no change in the Engine performance, i.e. the engine runs the same, then you know that your problem is likely ignition related. Check the cap/rotor, wire, and spark plug. This can also be safely done with an inexpensive inline spark tester sold at most auto parts stores. The old school screw driver trick is risky, dangerous, and inaccurate. You are looking for a very hot spark, a blue flame as we like to call it.

If the engine performance does change, it shakes more, etc. Then you know that more than likely your issue is elsewhere, i.e. fuel delivery. Check fuel pressure, leak down, etc. If that is all good, you may have a messed up injector.

In all cases, I always recommend a fuel pressure test, leak down test, spark test, and a compression test. Just to give you a base idea of where to start looking next, and to be sure that the basics are covered.

A really good article on fuel trims is here: Fuel Trim?

Let us know, and good luck!

 

An update:

After a LIM change in December the 'very rough idle' stopped, however, the P0304 remained. As I posted in another thread:

I think I have finally fixed it. Hope this does not jinxed it.

I replaced the 4th injector. I wish I had the funds to have done the MFI conversion, but my budget only allowed to replace the single injector.

So far 3 trips and over 100 miles, no SES light and much smoother running!

 

I jinxed it. Right after posting this, I started up the Blazer and before I left the parking lot SES is back on. And it is P0304!

I'm starting a new post.