[mccviii]

Greetings astro family

I've been nursing my 03 astro for the last number of years. and I have hit a wall with what I think I can diagnose on my own. I suspect that a mechanic with a real time data analyzer could help pinpoint where the issue is, but I don't have a trusted mechanic with that equipment and don't want to go $earching for that guy/gal just yet...

This issue has been around for at least a year or so, seems to be getting worse over time (deterioration of a component). When I initially felt it, I thought it was from changes in the pavement on the highway making the van feel/sound slightly different. Now, the shaking/sound is more pronounced, and has a direct relation to gas pedal input. It can happen at various speeds depending on transmission gear, but for example, if I'm cruising at 35mph or so, and looking to sustain speed with "maintenance throttle" level of gas, the van will sound/feel like it's going over mild rumble strips. To get it out of the vibration zone, I can give it more gas (if traffic allows) or remove my foot from the gas pedal altogether. with no throttle input, the van idles smoothly.

I thought initially that the issue was linked to a specific RPM, but as the issue has grown more pronounced, I think it's closer linked to throttle input primarily. Plugs and wires were replaced about 2.5 years ago. Fuel pump was replaced a month ago, which seems to have slightly changed the character of the throttle response. The fuel injectors were replaced at a dealership before I purchased the van in 2016.

No engine error codes except for an occasional "open reference circuit B" code that will appear and clear on it's own. previously had a sporadic "cylinder 2 misfire" code but that hasn't appeared in months.

I fear that the problem lies in the injectors, being unable to supply proper atomized fuel at small throttle openings, causing stumbling, but theres an argument to be made for electrical/ignition components as well...

any thoughts or relevant experience to share?

thanks
C

 

[mccviii]

the subject in Chicago getting it's obligatory nice-day-of-winter wash

 

[Mmusicman]

What you describe "might" be the very common worn distributor issue. The worn gear causes erratic timing "at part throttle" only... idles fine and full throttle fine. It can happen in any gear, and virtually any speed, when vacuum is highest at part-throttle. The erratic jerking operation is often misdiagnosed as a transmission issue. It can be subtle or obvious. It only gets worse with time.

Can't say for sure this is your issue.. but it was mine on several vans now, as well as many others who've dealt with the same trouble.

I'm less inclined to believe it's an injector issue, since it was replaced already.
But it's always a possibility too.

Here's an excellent link on the distributor:

Astro-Safari-Info - Pancake Distributor Disease

Ah yes, the dreaded pancake distributor disease(PDD) again on GM Vortec Engines. This is a cap for the pancake style distributor used on 96 and up Astro/Safari vans.

sites.google.com

 

[mccviii]

thanks for the reply. I was hoping that the injectors would be safe as well, it's nice to hear a second opinion in that arena.
i have the Chilton's service manual, Ill get into reading about whats involved to replace the dist.

"
What is this random bucking/misfire feeling thing happening to my Vortec powered van? It usually shows it's ugly face when you are in OD with the TC locked up at partial throttle on a nice flat highway. Press on the gas it stops, let off the gas it stops, partial throttle it comes back.
Usually the bucking/misfire is worse in high humidity and rainy situations because the secondary ignition system is working on the very edge of failure. Can even cause a hard/no start condition. Sometimes it just shows up as a p0300 random misfire code, other times there is no code at all.
It's annoying, and it's costing you fuel mileage. Worst case is you ignore it and destroy your catalytic converter from the excess un-burned fuel heading into the exhaust, CatalyticConverterDeath. Plus your secondary ignition system is working harder which is really hard on your ignition coil, ICM, as well as the cap/rotor/wires as the energy is increased to try to overcome the added resistance(in the form of an additional gap)."


Certainly sounds like what I'm experiencing!!!!! kind of right on the nail....

 

[Mmusicman]

Don't over-think this. The distributor gear wear is quite common. I've personally found the distributors to be good for about 150K.. but experiences vary. It may or may not be your problem, but what you describe sure sounds like it... it was for me on more than one occasion (especially the part-throttle thing).

Fortunately distributors are fairly cheap (less than $100) and easy to install. Carefully mark old one before pulling, and be sure to drop new one in lined up identical. They spiral in.. so I make two marks (direction rotor points), one at top of gear, and one when fully seated. If done accurately, there will be no further action needed. Don't turn over engine. If it doesn't fully seat, you can tweak oil pump shaft with large long screw driver.

Even if it turns out not to be the trouble.. it very well could be soon enough anyway. Changing the distributor on these engines is almost like changing the plugs. Even if not needed, it will eventually need to be done anyway..in most cases.

 

[Mmusicman]

Here's my own video of my worn distributor that caused issues for me. The amount of play in old unit doesn't seem overly excessive to me.. but apparently the computer had serious issues with it. My guess is that it physically jumps around while the motor is running.. and I discovered the problem most pronounced at part-throttle high vacuum when timing is over 35-40 degrees.

 

[02GMC]

In support of what Mmusicman said - This takes me back a ways to an HEI distributor I had installed in place of points distributor in a 72 Chevy truck (I still own). Idle was fine, any significant throttle input was fine, but steady state cruise under light throttle was awful. Would miss pretty bad, but immediately clear up with throttle application (or release). Finally figured out it was an issue with the electronics on plate that would move when vac advance can got vacuum. Didn't happen at idle because dist was connected to ported vac source.

 

[mccviii]

sick.
this is great. ive been watching these symptomsslowly get worse and worse for quite a while, its amazing to have something directly to point to.

i'll replace the dist when i get the chance ( a new house and 4 motorcycles are first in line LOL) and will plan to report back my success.

are off brand distributors just as well for this? delco is 220 or so, generics are like 70...

 

[mccviii]

Surprise surprise

put a new distributor in (this one) and it’s been rock solid, practically jumped to life when I turned the key to start it. Taking a road trip next week, highly confident that it will perform better on the interstate now. Around town it’s been great.

thanks for the assist!!
Also replaced my oil pressure sender unit, while I was there. Much easier with the distributor removed, as a regular deep well socket won’t fit down to the hex on the sender to remove it. I changed it because the needle on the dash was acting erratic, dropping out randomly. That seems to be fixed now.

great!!

 

[mccviii]

Well unfortunately I return with bad news, the new distributor didn’t fix the issue. The 300 mile road trip showed me that the issue was still in fact there.
I have to assume the new distributor was installed correctly, it rides around the city just fine. But once it’s on the interstate at maintenance level throttle input, it has the telltale shake.

any other ideas for where to look?

 

[mccviii]

continued to chase this vibration issue in the engine until yesterday. replaced MAF recently because of a trouble code. Van runs smoother. Alternator output dropped intermittently recently on a drive, got scared and bought one to replace it. might as well put a new belt tensioner and belt on at the same time.

engine parts arrive, and the vibration issue somehow is the worst it's ever been. found the culprit. god damn exhaust heat shield that sits above the muffler. the last fastener had just rotted away and now it was sitting resting on the exhaust. about 10 teks screws later, the shield is very securely fastened to the underside of the vehicle.

happy/bashful to report that the original buzzing/vibration issue has been solved.

 

[Mmusicman]

the vibration issue somehow is the worst it's ever been. found the culprit. god damn exhaust heat shield that sits above the muffler...

Where I come from.. something "rattling" is different than a vibration.
Good job.. glad to see you resolved the trouble.

 

[mccviii]

Where I come from.. something "rattling" is different than a vibration.
Good job.. glad to see you resolved the trouble.

rattling is just a nonmusical vibration
no surprise that you're unfamiliar!

🤖