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87 G20 with a 305 Engine that runs like crap
#712021 July 28th 2016 12:25 am
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Alright so I picked up this beautiful 1987 G20 van, very good condition albeit in need of some TLC and elbow grease. Unfortunately, that describes the body better than the drive train.

She's got a 305, 5.0L V8 TBI, and it doesn't run worth a damn. Well I mean.. She starts up fine, but then the idle starts fluctuating and bogging, up and down, up, down a little longer, up, down a lot longer, up, down a really long time...then slowly she'll bring herself back up and stay there, "purring". Doesn't seem like she runs that bad when sitting there idling, but if you whack the throttle too fast she'll knock? (clack?) a couple times til RPMS pick up. Gradual onset of throttle yields no knocking or funny noises that I would know enough about to discern.

When I was picking up the van, she seemed like a gutless turd. It took quite some time to get her up onto the trailer, very poor throttle response most of the time, sometimes it'd pick up and go but it took a few tries. As the engine got hotter while it was under pressure, it started knocking a bit, although it wasn't consistent and went away.

When one turns the steering wheel, it really bogs the engine down.

Also, the automatic transmission left me a big dandy love spot on my driveway, and reverse engages slow.

I know I got my work cut out for me Doc, but I gotta know. What's the damage? What am I in for?

Re: 87 G20 with a 305 Engine that runs like crap
BungoBass #712023 July 28th 2016 12:49 am
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Well, first what have you done so far to the engine? When i start looking in to a vehicle i check the fluids, all of them, Change the oil, flush the coolant (if needed), top off steering fluid, brake fluid, basic stuff, then i give the vehicle a bit of a shake down to see what it all needs.

I would start with the oil, get it changed and to the right level.

As far as the poor idle after first start up, it sounds like your engine is "hunting" adjusting air and fuel to try to keep the idle consistent, i am not sure about the 87, but since its TBI it should have codes, you should see a connector under the dash, you can use a paper clip and jump 2 of the pins (a and b, they will be the 2 on the upper right of the connector if the connector is screwed to the underside of the dash correctly).

after the pins are jumped you will see your check engine light flash, the codes will come out as quick flashes fallowed by a pause and more quick flashes, the first set of quick flashes if your first number, the second set of flashes is your second number, each code will flash 3 times before moving on to the next code, your first code will be 22, it will flash 3 times, then your stored codes will flash, after the last set of codes flashes it will flash code 22 again and start over.

things to check for a poor idle at start up is your idle air control, your throttle body position sensor, injector flow, fuel pressure, i would add O2 sensors to the list but on a cold start your sensors are in open loop, the computer ignores readings from the 02 sensor until the engine is hot then it will go in to closed loop.

since its a cold start issue, i would start with looking at your idle air control and throttle position sensor if your injectors look like they are working properly.

oh and it would be a good idea to change your spark plugs, wires, cap and rotor just so you have good components to start with during diag.

Re: 87 G20 with a 305 Engine that runs like crap
BungoBass #712032 July 28th 2016 8:28 am
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Welcome and congrats on the van.

Everything that SonnyLada said is good stuff, but I would also throw in a good inspection (at the least) of all the vacuum lines. Vacuum lines get neglected in cars where they are relatively easy to get to, let alone a van where they are more of a pain. Vacuum leaks can cause all kinds of havoc with drivability.

Just a thought. Good luck and let us know what you find as you dig in.

Re: 87 G20 with a 305 Engine that runs like crap
BungoBass #712069 July 28th 2016 8:48 pm
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Alright, so as per the previous owner, the van didn't run, sat for a couple years. he changed some things, fuel pump and filter, as well as coil, spark plugs, couldn't get it to run. changed the distributor and it started running again. So it seems pretty fresh as far as spark delivery is concerned (as per previous owner, so who knows).

I myself, the very first thing I did was take care of the vacuum lines. At least the rubber ones from the vacuum reservoir running back to a check valve coming out of the intake and splitting two directions: one running to some 5 wire dealiewidget that has a linkage to the throttle plate (Throttle Position Sensor?) and the other to a little black box thing which I have no idea what is, could be one of those things you speak of. And thats pretty much all I've done, save for play around with the distributor a bit (a "see what happens when i do this" type thing, i figure thats the only way to learn)

Oh, speaking of that. So i fussed around with the distributor with the black tan wire unplugged, got it kind of in the middle of the range between the bogs, went through the process of unhooking the battery for a minute before plugging back in and when i fired her back up, she seemed to run at normal idle a bit longer before going back to "hunting", but seems like generally lower idle, almost stalled out. Anyways was that initial clarity the computer taking time to catch up or something?
Also, hopefully my experimentation won't hurt anything.. I know nothing about flowers but I am very driven to learn. Make it or Break it lol


I'd get immediately on checking everything yall have listed, except that I'm not really sure what's what right now. I've got a Chiltons service manual coming, should be here tomorrow or saturday.

Yall have any photo tutorials? "This thing right here is such and such, that thing is the dealiewidget and right next to it is the thingamajigger"? Ways to test, repair components described? I seem to have trouble using the search function and what little comes up doesn't have the information I need, but I'm actively looking for any and all information pertaining to what I have here.

Last edited by BungoBass; July 28th 2016 8:50 pm.
Re: 87 G20 with a 305 Engine that runs like crap
BungoBass #712073 July 28th 2016 9:40 pm
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Just because he said he put in new parts, new parts arent always good out of the box. It really sounds like the ICM under the cap on the distributor. You also may have a cracked spark plug wire.

The other thing that comes to mind is the fuel flow censor.

The computer needs millage on it to correct the settings. Starting it in the driveway will not reset the computer. Get it going the best you can & put some miles on it. Driving it will put a load on it, that you dont get in the driveway.


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Re: 87 G20 with a 305 Engine that runs like crap
frscke1 #712080 July 28th 2016 10:28 pm
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The "ICM" that frckse1 referred to caused the same problems on my original 4.3L. I changed throttle position sensor first due to the "hunting" you refer to. No help. That thing under the distributor tends to overheat and fail a lot. I think i changed it twice in 5 years. It has special white heat sinking grease to cool it through the distributor body, but i dont think much airflow gets there on the vans. I think it was about $50. I would try that.



1992 Chevy G20, 110" wheelbase, Mark III conversion, L31/4L80e swap, Express wiring harness.
Re: 87 G20 with a 305 Engine that runs like crap
BungoBass #712127 July 29th 2016 4:23 pm
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Hey there and welcome to the site. Youtube has a lot of automotive tutorials. Coldwarmotors. Fun with cars. Eh Can the motor brearhe? Proper fuel delivery? Clogged exhaust? Muffler or Cat.

So, a factory service manual will certainly help. Ebay... Parts manuals with exploded diagrams are cool, electrical manuals too. It is fun to learn how modern engines operate.

I second all mechanical sentiment expressed.

You will find using a multimeter will be helpful to check sensors, voltage, resistance, continuity.

Correct firing order and correct timing are always a big plus as well.

Good wrenching!

Re: 87 G20 with a 305 Engine that runs like crap
BungoBass #712140 July 29th 2016 10:08 pm
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I messed around a bit today. broke a few crappy 80s plastic pieces including a plastic vacuum line which i cobbled back together by sleeving with rubber line. And that was to get at what I learned was the EGR solenoid lol. Also checked the firing order by tracing spark plug wires back to their respective cylinders.. seemed to be alright. Also found the fuel filter tucked up behind the passenger frame rail, behind the rear wheel. Looks new, I think it's alright for the time being.

Unfortunately, I look at the engine and all its workings and i just kinda freak out a little, im afraid ill end up breaking the whole damn thing. I wish I knew a lot more about what im looking at.. Perhaps the service manual will help, when it finally hopefully arrives tomorrow.

One question.. so while the engine was sitting there idling, I decided to unplug a fuel injector. The idle roughened. I plugged it back in, smoothed out. Unplugged the other one and the engine dies. Is one of my injectors perhaps not functioning at capacity, so its depending on the other one?

Re: 87 G20 with a 305 Engine that runs like crap
BungoBass #712141 July 29th 2016 10:57 pm
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Also: Man, the wiring looks pretty rough.. Theres a few wires that seem split out or that are exposed, one going down to something plugged next to the oil filter? and the pink / white plugs that go to the top of the coil look kinda smashed. here and there, not so healthy looking. I would hope to not have to change the wiring harness though..

Still, It'd probably be good to go through and clean all the connectors, aye? and whats good to clean them with? Also, dielectric grease? Also, anything to bear in mind before unplugging things willy nilly? Probably disconnect battery first, aye

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