I've got a 97 blazer. Whenever the tach reaches 1800+ (mainly cruising down the highway) it begins to act like it's not getting fuel. My first assumption was spark but the plugs, wires, cap, and rotor aren't even 4 months old.

While cruising down the highway at 65mph it tachs about 2000. It will sporadically give a shudder - almost like a small misfire. No check engine light though. There's no consistency to the shudders either. Thoughts? I'm thinking my injector is going bad on me, but I'm not sure. Fuel pump is about 2 months old since that crapped out.

 

Check fuel pressure and leakdown first. Most auto parts stores rent the tester for free, (your deposit is returned). They also sell them for ~$40. There's a service port on the driver side, next to the distributor, probably has a black plastic dust cap on it. Connect the fuel pressure tester to the port. In the underhood fuse panel, there is a vacant terminal next to the fuel pump relay. It goes directly to the fuel pump and it is the "fuel pump prime terminal". Connect a jumper wire from battery positive to the terminal.



When the fuel pressure reading stabilizes on the tester, make a note of it. Disconnect the jumper wire. Wait 10 minutes and observe the fuel pressure reading on the tester. Make a note of it. Post the results.

 

97 blazers don't have an underhood fuse panel. Unless it's stupidly hidden somewhere, I have yet to find it. Even my owner's manual only lists the fuse panel in the driver's side of the dashboard in between the dashboard and the door. Would simply hooking the pressure tester up and turning the key to "ON" to run the fuel pump for a few seconds work just the same?

 

Could it possibly be a worn out ignition coil? Because if it isn't fuel related it would more than likely be a spark problem. The blazer only has 140k on it so I doubt it has enough leakdown to cause this.

The easiest way to describe it is that it acts like the fuel injectors are too big for the fuel pump so it begins to have fuel cut-out problems (like if you put bigger injectors in a car but don't change the fuel pump to put out more pressure). And like I said, the fuel pump is brand new.

 

Just read something interesting:

Someone else had a similar problem with a 97 blazer. He had run out of gas and then once he got gas in it it started shuddering slightly. The fuel filter was slightly clogged because of some debris that was in the bottom of the tank. Would make sense right? Blazer drives fine but get it into higher rpm where it needs more fuel and the filter blocks the flow just enough to make the engine stumble.

 

Good catch on the fuse panel, sorry, only 98 and newer have an underhood fuse panel. Each time you turn the ignition to the run position, (don't start the engine) it will activate the pump for ~2 seconds. Cycle it a few times until pressure comes up and stabilizes.

Fuel starvation at higher RPM could be caused by a restricted filter. But it also could be caused by low volume from the pump. It needs to be capable of supplying a quart in 30 seconds. Just cuz the pump is new, doesn't mean it's good. That's why we need to check it. What brand pump did you install? Several aftermarket pumps do not meet GM factory specifications necessary for this engine. Certain manufacturers have a high failure rate too: I've seen several fail, right out of the box. Check around the forum, I'm not alone on that one

Anyway, check pressure and leakdown and post the results. That will tell us where to look next.

 

It finally threw a code. P0300...random misfire. Not like that really helps me though. Rear O2 sensor was staying high so I'm fairly certain that eliminates fuel as my problem. Ignition coil? I remember having problems starting it before I did my fuel pump and when I checked spark it seemed weak (it already had new plugs, wires, cap, and rotor put on about 1 month prior to me checking spark)

 

These things are really fussy when it comes to plugs, cap & rotor. AC Delco should be used for these parts. The ignition coil is a possibility: sometimes they will arc and ground out causing a misfire or completely stall. Faulty plugs, wires, cap & rotor are usually what cause the coil to arc. Once it starts to arc, there's no stopping it and it must be replaced. Spraying a mist of water over the secondary ignition parts while the engine is running, will make spotting the problem easier, (best to do it in the dark).

 

It's the cap and rotor. I took them off and cleaned the scoring off and it runs much better. Damn autozone garbage. I don't want to spend an arm and a leg for a cap and rotor. What about ACCEL brand?

 

Autozone Duralast is probably the worst cap on the market. At one of the chain parts stores, Accel, (#120142) is $53. AC Delco, (#D328A) is $44. AC Delco caps are good for 100K miles, IF you put silicone dielectric grease on the terminals, (inside and out). Why spend more money and take a chance? It's a no brainer. Check Amazon & ebay, probably find it cheaper.