My blazer details:
1995 4x4 2 door LS auto, obd 1.5

I bought it Feb of last year and a month or 2 after it was having trouble staying on. I replaced the MAP sensor which fixed that problem. Replaced the entire cooling (preventative maint) and steering system when I replaced the front diff and rear axle with ones from a 2000 zr2. Factory intake had a hole in it, replaced it with a k&n unit. 4th gear went out and started getting codes for the o2 sensor. Replaced the 02 sensor, trans filter, harness, shift solenoids, and fluids. It ran better, had 4th gear again but it wasn't 100%. The next issue I had was the bucking, it would struggle over 2500 rpm so I replaced the fuel filter, spark plugs, wires, cap, and rotor.

It ran fine for about 6 miles and died. Parked it until March of this year.

This year, I took it to a shop to fix some leaks and address the no-start issue. They replaced the spider injectors, fixed some of the leaks and I got it back in June. It was firing up like a champ but the trans was still weak and it was also having an issue running hot with the coolant boiling out of the reservoir. I took it back to the shop to have the trans rebuilt as well as addressing the coolant issue. They replaced my rad stating they found coolant with the trans fluid. Got it back and it was shifting much smoother but 4th was hit or miss. Took it back to get that fixed and now it shifts and was running like it was supposed to minus it running hot so I replaced the fan clutch. This is the point where I start having issues the bucking issues again. In September, I went for a simple night drive and as the RPMs got close to 3k, it started hesitating again. As the days went on, I realized it was getting worse. The hesitation would happen higher up around 3-3300 RPM range and as it warmed up to operating temp, it would happen between 2200 and up (wasn't consistent between 2200-2500 but it was consistent closer to 3k). I took it back to the shop and they tell me it's the cat. I went to an exhaust shop and got it replaced and the guy tells me the cat was toast. I start driving home and it was fine for a moment but about 2 miles on the street, the issues came back with a vengeance and now, the problems starting around 1900- 2000 rpm.

Before I replaced the cat, I took it to the dealer and they couldn't run any diagnostics because they didn't have the proper scan tool. Does anyone have any thoughts on what the problem could be?

 

That’s quite a story. Let’s try to unpack some of this.

Your problem is is somewhere in the following areas:

Fuel delivery
Air/vacuum/exhaust
Ignition
Timing
Mechanical
Sensors/ECM/wiring/connectors

When you were told that the cat was toast was that because of an exhaust restriction, increased emissions, or both? Most of the time when a cat dies there is an engine performance problem and that needs to be straightened out or the same thing will happen to the new cat.

You have ODB 1.5 but yet you talk about reading codes which many have issues with. What is the capability of your scanner, can you read live data like sensor values?

You should do the fuel pressure test in the sticky, especially leak down. If your handy, it would be great to see that fuel pressure while it’s rev limited, you can tape the fuel gauge to the windshield.

Do you have a recent compression test?

Lets start there,


George

 

Thanks for the reply George, I wanted to be as thorough as I could and covered everything that was replaced.

As far as my cat, I wasnt given any clarification. All I know is when the exhaust shop replaced it, there was at least some form of problem there (exhaust shop was independent from the shop that diagnosed it). Previous owner did his own cat repair and it looked horrible to start with. I'm sure that thing was on its way out before I got it.

I have a Zurich zr13s from harbor freight which has capabilities for love data but sadly it won't work on the blazer since it's too old.

I do have a compression and fuel pressure tester so I can check to see where the values are at tomorrow.

 

That's a shame on the scanner capability because that would help us a lot.

I'll look out for your fuel pressure and compression test results. Make note of the spark plug condition.

Also, look at the spark at a couple of plugs when its running good and again when its running crappy. Look for 1" of strong blue spark with a regular cadence.


George

 

Wanted to give an update. Haven't been able to accomplish much. In between houses and don't currently have a garage but I did run the fuel pressure tester at the port under the hood. Key on, gauge shoots to 60-61. Once it's done priming, drops to 59 and slowly drops. After 10 minutes, dropped to 43.
Took it for a drive with the gauge taped to the windshield. At idle, it holds pressure @ or over 52. When I give it gas, fuel pressure goes to 60. When it starts hesitating @ 3k RPMs, fuel pressure is still at 60.

I figure with that test, there is a leak somewhere. When the weather gets a little better, I'll conjuring the pressure test at the filter and pull the spark plugs for the compression test.