ORIGINAL: atwistd1 via PM

Hi its me again in need of some advice, Here is an update on my truck that you gave me some suggestions on "O2 sensors? or more?" it got to the point that i could not even take off from light so i took it to a shop here on ling island the guy is a former GM tech that left to open his own shop. He brings my car in barely running and pulls the fuel filter... totally clogged. replaces it and starts the truck... runs ok but when running the rpm range and pegging it still bogs misfires stutters etc. So he hooks it up to this $10k diagnostic machine and proceeds to check everything 5 hours worth. cap and rotor ok, Fuel pump ok 50# off and 55-60 running. all O2 sensors are resetting and reporting fine, (one is a little lazy but he said not to worry) air filter good, took out MAF and cleaned it, put it back still same problem. strange thing is that some voltage reading on the MAF was too high 6.change, not good he says, he squeezes with his hand the black part the plug goes into and voltage reading drops to normal level, tested TPS and said it is okay, he has deducted that the poppets on 123 cyls are sticking probably from the plugged filter cause his machine shows random misses on 1,2,3 cyls and occasionally if hit hard 4 or 6 goes. also thinks that the readings on the MAF might have something to do with it. tells me that i would be wise to replace whole spider if it turns out to be that rather than just the stuck poppets. he reffers to a TSB stating to clean poppets, he gives me some chevron tercron to run on about 10 gals of gas, he said it is only about a 20% chance of working but its worth a shot for only 6 bucks. told me to then test another MAF in there to see if it fixes the problem. I ran the techron on the way home, car still hesitates and backfires if hard acceleration but is about 50% better. Also if i feather the gas and take off normal it is okay til it shifts into second gear then it bogs, i let off gas and it picks up and goes again. what do you make of this, i really hope it is not spider cause he told me it is like a 900.00 job and i really can not afford that. oh yeah he tested cat to see if it was clogged and it was ok. any advice would be greatly appreciated

ORIGINAL: swartlkk

atwistd1, I hope you don't mind me restating your PM to me here. I am just putting it here so that more people can try to help out with your situation. I don't claim to be all knowing and there are some very knowledgable folks here that may be able to see things that I most likely have missed.

It is very possible that clogged poppet valves are to blame here. GM has redesigned the SCFI spyder to a MPFI setup with injectors where the poppet valves are now. This revised spyder is a bit cheaper than the replacement SCFI spyder and is MUCH more of a reliable design. We can talk you through the replacement of this item on your vehicle if you have the tools to do it yourself. If not, that $900 quote from your mechanic seems high. I would suspect around $500-600 for this repair including parts.

Another posibility is a worn distributor gear. I have been hearing a lot about the gear on the bottom of the distributor (that is driven by a gear on the cam). This would retard the base timing to a point where power would be affected and it would most likely be more noticable the higher the RPM. The only problem is that to properly check this gear, the distributor must be pulled.

Others, please have a read through and give your thoughts on the matter.

ORIGINAL: swartlkk

Ok, I just had to include that. I guess the next thing would be to do an injector cycle test while monitoring the fuel pressure. I remember doing this on my old Intrepid, but the injectors were a bit more accessible than on the blazer. This was done by removing the electrical connector on the injector and installing a switch. The switch would apply voltage to the injector to actuate it at a pulse width of 3ms. With the engine and key off (but fuel system pressurized), the switch was activated and the pressure drop recorded. For my Intrepid a pressure drop of 3 or more psi would result in a bad injector. Move on and do them all.

However, for the SCFI injection system, this type of test could be misleading. Because the injection setup is one with an electronic injector connected to a poppet nozzle, the injector may very well be operating correctly with the poppet nozzle leaking fuel past itself. This could result in fuel being dribbled into the intake port the whole time the engine is running instead of being sprayed in only when the intake valve is open on that particular cylinder. Chances are if one cylinder is doing it, there are probably more.

One thing that hasn't been suggested yet is to have your fuel system Professionally cleaned. Many places (oil change places, repair shops, even the dealership) have a set of chemicals that bypass the main fuel system on the vehicle and run this cleaning agent through the fuel injection system. GM actually has a TSB on this very subject. Bulletin # 00-06-04-003B refers to the proceedure for the dealership to go through to perform the fuel injection cleaning. Many of the alternate fuel supply cleaning methods work just as well as the dealerships method (regardless of what the dealership will say). I would start there.

They also have another TSB on fuel injector sticking that only applies to vehicles with California Emissions (RPO YF5) that allows for free injector cleaning and/or replacement of the SCFI sypder with the new MFI spyder if applicable. The wording however leads me to believe that this is only for SCFI equiped vehicles with RPO YF5 registered IN California.

With all of that said, you could probably drop $100 getting your injectors cleaned and end up with the same problem a year or two down the road. The PN for the MFI spyder assembly is #12568332 and is available from GMPartsDirect.com for $153.90 + s&h which is usually fairly high. Even if the S&H is $40, it is still a cheap alternative to a bandaid fix. If you do the work yourself, you're only out the cost of the MFI spyder assm.