I had a ‘99 Savana with the 305 version of this engine, the L30. HATED this engine. At 100K, I had to do the intake gaskets. 190K, it blew a head gasket, between 5 & 7 (like all small block Chevy engines eventually do...) and I scraped the van.

I’m gonna suspect two things here:

1: You messed with the fan. Go over what you did with it to remove it and re-install it real well.

2: This vibration that happens between 4,500 and 5,000 RPM. What gear does it happen in? Same vibration regardless of first gear, second or third?

 

the fan, the accessory belt, and the distributor are the only moving parts i removed and replaced. Ill check the fan out eventually, but im at school right now so i dont really have the resources to mess with it.

and yes, vibration is in every gear.

 

OK, you’ve eliminated any drive train/transmission issues.

I’m of the opinion that it’s something with the fan or the thermostatic clutch.

Do you still have the old belt? Although it’s probably far fetched, it is possible that the new one has a problem. Swap the old one in and see what happens.

It’s something you did/touched/messed with.

 

Does it do it free revving? If so, you can rule out anything accessory belt driven by simply removing the belt and revving it up.

CMP retard is definitely in the tech 2. You need to find somebody competent with a tech 2 to help you with that but, it will set a DTC for that if it is off significantly, on the second ignition cycle. I'm still leaning towards a sticking poppet or other fuel system issue. If fuel pressure drops below 50 psi under high demand, even properly functioning poppets will stop opening and create misfires.

 

Good question and good idea.

 

how would the fan be installed wrong though, arent they a one way fit? When the engine is idling it appears perfectly in balance, i dont notice any wobble or anything of the sort.

im willing to try anything at this point, but that old belt is long gone. I'll try removing it completely sometime like 05 said.


great idea. Im not sure about free revving, i really dont like revving it that high without any load on it, and it wouldnt really hit that RPM long enough for me to feel it.

would you happen to know where it is in the tech 2? This guy seemed to know his way around it pretty good and i didnt see it either. There is a good chance it could be an injector issue, only because there isnt much left that it could be...

I'll also check if can log fuel pressure in HPTuners.

Thank you for the suggestions!

 

It is just a parameter in one of the engine data lists. IIRC, it only updates on engine startup but, it has been several years since I worked at a stealership. It should say something to the effect of "CMP retard" and give the parameter in degrees.

The truck has no fuel pressure sensor so, you will not be able to log it. Screw a pressure gauge into the schrader valve, tape it to the windshield and go for a blast around the block. You will need the (accurate) fuel pressure gauge hooked up to do the injector balance test with the tech 2 as well.

When these things were coming into the dealer regularly for drivability problems, 90% of them were fuel system related (injectors, regulators, pumps and filters), 5% ignition system (cap and rotor, coil wire arching), 4% wiring (something rubbed thru, a terminal got loose) and 1% hard parts (burnt exhaust valves, clogged up cat converters, loose crank pulley<-good one! etc).

Never ever saw a bad clutch fan on an "R" motor. Not a single one in over 10 years of working on them every day. They are also damned near impossible to install incorrectly. Only thing I can think of there would be if you broke the plastic blades and threw it off balance but, I kinda doubt you would be scratching your head wondering what the problem was in that case. A bad water pump bearing may do it as well but, you would notice that reinstalling the fan (free play of the pulley side to side/ top to bottom) and it wouldn't have just started after an intake job either.

A stuck poppet makes perfect sense to me, because I have seen it happen plenty of times. Pull the intake off for a gasket problem, get a tiny piece of schmutz in the poppet and bam, misfire when it goes back together. Some worse than others of course.

 

I dont have a fuel pressure gauge but theyre handy and id like to have one anyway so I'll just bite the bullet on that and check it out.

But actually you reminded me of something i completely forgot about. I replaced the waterpump because i figured it would be a good time to do it. I did NOT use a GM part, but i did use the best one available at the auto parts store and i think it may have had a lifetime warranty. If anything was funked with the bearing though i think i would have noticed it.

That said, the stock poppet is still making the most sense to me at this point.

 

That one seems pretty common, ive seen that on a lot of cars, wouldn't be something to worry about.