Having trouble pin pointing the problem. The blazer has 200k miles on it. It started idling rough just the other day. Changed fuel filter and added fuel system cleaning additive to the tank. Ran fine for a few days and then the problems really hit. Anytime at idle or holding a constant rpm while driving the blazer starts missing. I just changed the fuel pump thinking it was going out. Checked spark plugs and they are good. Could i have clogged an injector with the additives? The injection system is new to me so im trying to learn where to from here.

 

I did however notice the distributor cap was a cheap one. Lookedike master pro

 

 

I changed the MAP sensor and it is still no change. Idle is rough and everything smooths out after 1100rpms

 

I would suggest getting an AC Delco cap and wires regardless. I would check the fuel pressure if you haven't.

How do the plugs look? Miy 200k Blazer ran much batter after changing cap,rotor, plugs wires while fixing the lower intake manifold gasket.

 

I assume that if you have a misfire, then the SES light is flashing. You are going to need a capable OBD2 scanner to read the misfire counters and otherwise help with diagnosis. If you have an Android phone or tablet, for a 1998 Blazer I recommend the BAFX Bluetooth OBD2 adapter as sold by Amazon and the Car Gauge Pro app. It does a lot more than read codes. Lots of live data PIDs - even the infamous cam sensor retard (which you will want to check). About $35 total.

 

The SES light is not flashing. I pulled the Crankshaft Position Sensor and checked for Resistance. I got nothing. Would that mean a bad CPS or is the CPS one of those things you cant check resistance?

 

I just seen this and i think you may be correct. Hooked my timing light up to all the wires and 2 out of the 6 were constant with a hiccup every now and then. The other 4 were all kinds of crazy flash patterns. Ill change them and see

 

Changed the cap and rotor, no change

 

I think you need to ask yourself..... If I have a misfire, why isn't it being detected? Still need the scanner.

Read this. https://blazerforum.com/forum/diagno...4-5-6-a-35153/

If you have a misfire and it is not being detected, then there is a list of requirements for doing the DTC check. Something is preventing the misfire from being detected as such, provided the SES light is operative and no codes are being set.

Disturbing the crank position sensor is not a good option. Changes the calibration stored in PCM for misfires, and can require a Crank Sensor Relearn.

Crank sensor testing involves verifying power and ground circuits going to it - then testing the duty cycle on the third while cranking engine.