Chevy Astro and GMC Safari Forum banner

No power during load or long grades

9K views 45 replies 11 participants last post by  c.zhou57 
#1 ·
Hey there, want to pick your brains on this issue that I'm having.. I searched the forum and tried a lot of the various testing/fixes that are commonly recommended, but am not having any results.

1996 Astro AWD. 135k miles.

The van feels like it's very short on power, especially going up hills. Recently took a trip that crossed the Sierras and couldn't hold anything past 60mph on long grades. It's also very sluggish off the line. This has been ongoing for a while (since I've owned the car ~10k miles ago) and I haven't figured it out, despite doing various fixes:

New tune up: plugs, wires, rotors, air cleaner, oil changes, pcv valve. Double checked and triple checked the distributor was lined up at TDC.. it's correct.
Took off the pre-cat o2 and drove it to see if the cat converter was plugged. Nope, problem still persists. Van has a stable vacuum when holding 2-3k revs at idle.
Fuel pressure is at 60psi during prime/start up, idles at around 54-56psi. Snapping the throttle brings it up to 60psi... seems to be in normal operating range. New fuel filter. Ran a few bottles of Techron through the system.
Cleaned MAF and carbon deposits off the EGR valve
Dropped tranny pan and replaced filter. Oil was a bit dark, but not burnt. Very little shavings on the magnet. Filled with new dexron. No hard shifts or slipping in the transmission.
Drained/replaced front/rear diff and transfer case oils. Didn't see any abnormalities there.
There are no CELS, car doesn't feel like it's mis-firing or stumbling, even when pressed at load. Starts up every time on the first crank without any hesitation. Just doesn't go anywhere fast..

I'm extremely stumped and am running out of ideas. Hope someone can lend a hand and help me figure out this problem or point me in the right direction.....I'll be very grateful
 
See less See more
#2 ·
I'd next check the coil and ignition control module. Sounds like ignition parts are sufficient at idle or under light load, but aren't quite enough under heavy load.

Oh, but wait: what grade of gas do you put in for the hills?
 
#3 ·
Thanks for your quick reply! I'll check into the coil and ignition control. Are there specific procedures that you recommend for testing?

I pump 87 gas, usually from the local Safeway (Grocery store chain here) or other known branded fuel. I stay away from the unknown gas stations.
 
#4 ·
In the hills, you need to use at least 89 octane, especially for the long grades.

Check for spark at the coil, then check for spark at the plugs. Good hot, blue spark at both is required. Also inspect the body of the coil for any cracks or arc traces.
 
#5 ·
Looks like the only thing you haven't mentioned is the fuel injector spider. I'm not sure how to check this... but I have seen people post some pretty amazed results with new ones after complaining of weak power. I may have a similar issue.

Again, no idea how to determine if the injectors are all good or not.
 
#6 ·
Thanks a lot for your responses. Didn't know that about 89 fuel. I'll keep that in mind when taking a trip in the future.

From your experience, would you recommend checking the spark with a tester or by grounding out the spark plug? I've ran into a very detailed website on the issue :
http://easyautodiagnostics.com/gm_misfi ... ests_3.php

They seem to recommend using an HEI spark plug tester. What would you recommend?

I haven't checked into the spider as it's pretty hard to get into. Saving it for the last, but I suspect it possibly can be the issue. Maybe a stuck injector perhaps? The pressure regulator on it is holding at 52+ psi when I key off, which is good, since I read that is one of the more common issues with the spider injectors. I don't seem to see the engine hesitating or missing though.. but I may be completely wrong

Is there any way to look at the injectors without tearing into it? I've read about noid lights and the like .. but it seems that since the spider is one whole assembly, it would be harder to test each injector individually.

I have a bluetooth obd scanner and torque app.. Is there something useful that I can get out of there? I think my PCM is one of the early ones that doesn't release too much information besides the general info. For example, many of the GM PIDs don't seem work on it..
 
#8 ·
Corsemoto said:
Plugged catalytic converter?
Hey Coursemoto, thanks for the response. A plugged cat was one of my top guesses. I checked for a plugged cat by disconnecting the o2 in front of it and taking it for a spin. There wasn't a drastic and noticeable improvement. Unconvinced, I hooked up a vac gauge and revved the engine 2-3k and held it at idle. The engine held a good vacuum at around 18 inches. :shrug: :banghead:

Thanks for the ideas guys, keep em coming.
 
#10 ·
The injectors in the spider assembly are just poppet valves. Noid lights won't work, they're for the injectors that are individually fired by impulses from the PC. You said you checked that the distributor is at TDC, but did you check the timing per the smog tag? It always pays to start the diagnostics with the basics first then move down the tree.
On the subject of injectors, when was the last time you ran a good grade cleaner through the fuel system? It helps to be sure that the injectors shoot a nice umbrella mist instead of a dribble. A couple cans of techron is always good for the fuel system. You can have good fuel pressure but crappy delivery at the intake and that'll affect performance.
 
#11 ·
Thanks for the tips, AstroPop. I'm still learning about the spider injector thingy. It seems like they can be a common problem in a lot of Chevys. :shrug:

I ran a bottle of Techron on the fuel for the last 3-4 fill ups. Still waiting to see if there's any results. A friend has a spare bottle or two of BG's 44k cleaner that I'll try next.

Could you elaborate a little on the timing? I was under the impression that the timing is set by the PCM and isn't adjustable.
 
#12 ·
c.zhou57 said:
Could you elaborate a little on the timing? I was under the impression that the timing is set by the PCM and isn't adjustable.
That is true. Have to get programmer for big bucks. Or get a cable and free program, take a college course in programming. Listen to how computers are better and easier, if you get frustrated trying to do it. All the while if you post your results absolutely nobody knows how and can help you or explain it to you.
Sorry I can't help taking these little stabs.

It can be done it just cost alot of money and will take a month to learn how or find somebody who can. Truly easier than loosening a little bolt and turning the distributor in 5 minutes.
 
#13 ·
I was just thinking to myself re: spider injectors. I'm trying to learn the diagnosis of it.

How can someone diagnose a stuck poppet valve externally before tearing into the manifold? I know a fuel pressure bleed down test would diagnose the regulator. Would the bleed down test also test a stuck open poppet valve? How about a stuck closed valve?
 
#15 ·
Haven't tested the TCC. Never thought to check it.. Same with TPS, MAP, or the IAC. Thanks for the suggestions!

Interestingly enough, removing the o2 didn't trigger a code. I have 4 o2s (1996 model), one on each side of the engine and one immediately before and after the cat. I removed the one immediately before the cat. I was waiting for a code to appear during my drive (30 miles RT through varying terrain/speeds) but it never came. Maybe it needs a few drive cycles before setting off the code? :confused:
 
#16 ·
You should do something to purposely trigger a code to make sure there isn't something seriously wrong with the computer. Usually removing the plug on the MAF sensor or something simple like that will trigger a code. Maybe connect a scanner to see if you have any codes set but the SES light has burned out!

The IAC would only be an issue is if was jammed or the rubber plug disintegrated. Simple pull and test. You would probably have other issues if it was failing.

Testing the TCC will be very difficult if not impossible without a dealer scanner to monitor its realtime duty cycle. Some scanners can tell you when it's locked up though.
 
#17 ·
Can you lay your hands on one of those bluetooth computer hook ups? That will give you a lot of information when using the right app. The Apps are available for free and paid for iPhone and Droid. You can read engine temp, O2[/sub], MAP, EGR and many other readings. Well worth the small investment for diagnosing problems, plus it works on many different vehicles. It can also tell you if your computer is even alive! (check the fuse).
And no, the code should have come up real quick once the computer reads the engine at normal operating temp. So maybe temp sensor or non-operating computer or bad O[sub]2sensor(s)? Here is where the bluetooth reader would help without having to take things apart. If the computer doesn't read the engine as up to operating temp it won't set codes and won't kick in to run things, you'll be in the limp mode.....?

here is what I use:
http://www.ebay.com/itm/Mini-ELM327-V1- ... 1e8e19783f
 
#18 ·
A sticky poppet valve on the injector would throw a misfire code on that cylinder.

Like was said above, does your SES light come on when you turn the key on? If not, you have a burned-out bulb.

Time for more diagnostics ;)
 
#19 ·
I remember having accidentally left off the MAF sensor at the intake tube and that set off a code, though not instantly.. Maybe a few or 10 miles down the road. That's why I was wondering why the O2 didn't register a code .. maybe it's looking for certain conditions to set or a set number of errors before triggering the CEL. :shrug: Just a guess..

When scanned by the tool, there are no codes present. I have the bluetooth $25 ELM clone adapter and Torque pro. It's able to read codes and read some basic live data. The GM specific extended PIDs doesn't work.. I haven't figured out if it's my early obd2 PCM (1996) not having the functionality .. or my cheap adapter.. or both. It would be great if I can pull into the misfire data, for example. I'm not getting any indication from the PCM in terms of CELs.. I would expect at least a rich condition since my mpg is terrible.. but one step at a time.

Any Torque/PCM experts out there?

Thanks for all the suggestion, guys.
 
#20 ·
I've had a similiar issue as well. My trusty mechanic who sadly passed away explained to me the one bad thing about older models that have low mileage on them. Carbon buildup in the engine. He performed a fuel injection service. Not the seafoam stuff, they actually pull the fuse for the fuel pump and hook up a machine that has a detergent and fuel solution. He ran it for an hour in the shop . The throttle response was completely differnt after the service. Just a thought.
 
#21 ·
Hey guys, a new update. I pulled the distributor to check the gear. I see shiny spots, but it doesn't look terribly worn or anything... just enough to show some wear. How does someone tell if it's acceptable?

Also, if I do end up replacing it... Does anyone have experience with the $55 dollar ebay aluminum distributors? Yay or nay?

This can't be the cause of my problems, can it?? Seems like there's gotta be more to the puzzle... Gotta keep digging.
 

Attachments

#23 ·
Hey Guys, just an update to the problem. Got so frustrated at the problem that i took the doghouse off and replaced the cap/protor/plugs/wires again with Delco parts. I cheaped out last time and got off-brand parts. I was able to dial in the CAM retard to 0.5 degrees with a borrowed scanner. My best efforts to line it up visually TDC produced a -15deg reading. Had to grind an oval on the hold down bolt to get it to adjust to spec. The van idles somewhat better now... maybe that's the placebo talking. However it still has the same bucking and loss of power at speed.

Looked up the problem some more and now think it has something to do with the torque converter. My problems seem to be consistent with the p1870 code, although no CEL is present. Hard 1-2 shift and shuddering on the freeway at around 50-55mph. Since I still have the scanner on me I'll go on a drive over the next few days and monitor the TCC components and see what I can deduce from there.

I've got a lot to learn about the tranny components and diagnosis...
 
#24 ·
Hmmmmmm. OK I'm way curious. You connected a scanner that allows you to see the timing and you turned the distributor....and it changed the timing? Your van is a '96? I tried this with my '97 a few days ago and the timing didn't change at all. I moved the distro both directions with no change. What's your secret? I was under the impression the computer will do just about anything to keep the timing at whatever it has in it's tables despite the actual position of the distro.
 
#25 ·
Cargo: You're right in that the computer will do everything to keep the timing same. No matter what position the distributor is I'm always at around 20 deg spark advance at idle. But what I was referring to is the CMP offset... Or CMP/CKP correlation. It's the meshing of the crankshaft and the cam sensor in the distributor for timing of the injectors... Something I found mentioned on this forum and others. You need a high-end scan tool to get this info as most sub-$500 scan tools won't provide the info. Since I think you mentioned having the Tech 2 you're all right.

With the engine running, plug in the scan tool and set it to read the CMP retard. I believe the sensor doesn't update at idle under 1200 rpms so snap the throttle to get its initial reading. Loosen the hold down bolt a bit and move the distributor one way or another and snap the throttle again to see a change. Play with it a bit and get it closest to zero. The spec is +/- 2 degrees from zero. Once you get it closet to zero tighten the hold down and you're all set.

After lining up my distributor to #1 TDC compression stroke, my CMP retard reading was -15 degrees off from 0. With the un-enlarged hole, you're only able to adjust maybe +/- 5 degrees.. I tried moving the distributor one tooth over, and got a CEL right away with a P1345 I believe. It was +60 degrees from 0.. so there's a 75 degree swing from my initial reading to being one tooth over. I moved it back one tooth and elongated the bolt hole for more adjustment and finally settled at 0.4 degrees.
 
#26 ·
My CMP retard was -15* and the manual for my '97 says -8* is about normal:





I'm still learning about this stuff so really I have no clue what I'm talking about. Gonna soon though because I have been trying to nail down my rough idle for over 6 months and I have spent a fortune. Tuning is my next priority. Pisses me off because my idle was smooth as butter not so long ago. No idea what happened.
 
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.
Top