Rough Idle, not throwing any codes, 97 C3500

[blueridge725]

Okay, I've been scouring forums and searching for answers, but keep coming up emptyhanded.

 

I have a 1997 Chevrolet 3500 2wd, 5.7 Vortec, automatic. 101,000 miles. I've owned it for 10 years, bought it from the local county park in 2007 with 45k miles on it.

 

A couple of years ago the truck started running rough when my wife was driving home. We had just purchased a newer vehicle, so the chevy got sidelined and parked. Recently, a reckless driver hit her on the interstate and totalled her vehicle, so I have begun to resurrect my old trusty chevy as a stopgap until we can find a replacement vehicle.

 

It was still running rough, and hard to start. Fuel pressure reading 50+, but did drop quickly. So I replaced the pump and filter a couple of days ago with a new AC Delco pump. Emptied the tank and put in fresh gas. The truck was also throwing a code for the coolant temperature sensor, so I replaced that at the same time. I also removed the 'throttle body' and cleaned the flapper, it was pretty filthy and i'd heard this could help with idling issues.

 

It starts easier now, doesn't die when I put it in gear like it sometimes did before. Fuel pressure as high as 63, but runs around 56/57. After shutoff it slowly drops to the mid 40s. Not throwing any codes.

 

When it starts it fires right up smooth, but then after a second or two it starts idling rough. Seems to smooth out when I give it some gas (hold it at higher rpms). The exhaust is still 'puffing', a whitish/gray just barely visible.

 

I had pulled #1 plug last weekend and it was pretty black. I checked it today and it was a light brown color, like it should be, as if all the soot had burned off it. I checked all the plugs. the front four were fine, the rear 4 were wet. Gap was about .057, was told it should be .060.

 

I thought they might be wet with gas, so I pulled off the upper intake manifold. It was pretty filthy inside, but I didn't see any leaking fuel anywhere. There was a lot of oil in the back half, so I am thinking the wetness was oil. Looks like the oil was coming in through the PCV valve.

 

I ran out of time for this weekend. Trying to find out where to go from here.

 

Cleaning the intake out and replacing the PCV may improve the look of the rear plug, but I don't know that it will fix how the truck is idling.

 

Is there further analysis I need to do on the 'spider injector' assembly before deeming it 'good'? It is the original, as far as I know, with the check valve type injectors. There is a lot of crud build up everywhere except right at the end where the 'ball bearing' is visible.

 

I have a scanner that will read fuel trim, spark advance, O2 readings, etc. But not sure where to find numbers to compare them to. I've worked on lots of vehicles, but this is the newest one--and without a trouble code not sure what might be going on with it.

 

Any suggestions on where to start/what to check. I don't want to just start replacing parts willy nilly. That being said, I don't mind spending money on it. Its been a good work horse, and other than routine maintenance and standard stuff (alternators, water pump, etc) its never given me any problems.

 

[Jsdirt]

Ahh, the spider. Another one of GM's fantastic brainstorms!

 

If there was any pooling gas visible when you first removed the intake, time to replace the spider. I suspect your regulator is worn out too, since you're seeing bleed-down when engine is off. Should remain steady for a few minutes without dropping more than a few PSI. Can't recall if the regulator comes with a new assembly - I believe it does, but don't quote me on that.

 

There's an updated design out too - you appear to have the 1st design. I'm willing to bet a few lines are cracked and leaking. If these systems don't have a specific pressure in each of the "legs" of the spider, it won't be enough to overcome the spring tension of the pintle, thus keeping the injector closed. If you're right on the borderline pressure-wise, it may spit and spurt fuel, resulting in a lean misfire, or dead miss. If the injector fails completely, you get pig rich misfires, which is what sounds like you have going on here.

 

Make sure you're sitting down when you price the assembly out, however ...

 

 

After reading through this quickly, I believe you've got a bad regulator. I'd still replace the whole 9 yards though, IMO:

 

http://troubleshootmyvehicle.com/gm/4.3L-5.0L-5.7L/testing-the-spider-fuel-injector-1

[blueridge725]

Ah, very useful information, thank you. I am going to try cycling the key with the spider electrical plug disconnected and see if I see any leaks.

 

There was wetness which I think was oil. But it had fuel smell to it. Perhaps it is all mixed up in there. A visual inspection of the lines under pressure should tell me what I need to know.

 

I'm not sure about the regulator. All the articles I read talk about a vacuum operated fuel regulator. There is an object that resembles a fuel regulator, but definitely no vacuum line to it. I was guessing it was an electrical regulator somehow, perhaps an integral part of the entire spider mechanism. (So much electrical on this truck---even the EGR. So few vacuum lines!).

 

I had previously priced the spider assembly Its pretty steep, but a small price to pay to have the truck running right.

 

I will update after I do the leak inspection, thanks!

[blueridge725]

Okay, I stopped by quickly to work on the truck this afternoon (its not at my house). The first thing I noticed was that the fuel pressure gauge was reading 50psi when I popped the hood (I left it attached to the schrader valve).

 

I unplugged the electrical connection from the spider assembly.

 

Had my brother turn the key, pump kicked in and shot the pressure up to 63. As soon as it cycled off (I can hear it even from under the hood since the engine isn't running) the pressure dropped to 55psi (instantly).

Then quickly dropped to 40 then below 35. within a minute or two.

 

Turned the key on again, pressure shot up to 63 then down to 55 when pump cycled off. Then dropped to 47 over the next 7 minutes.

 

Turned the key on again, pressure shot up to 63 then down to 55 when pump cycled off.

3 minutes 53

7 minutes 52

9 minutes 50

 

Turned they key on again, pressure shot up to 63 then down to 55 when the pump cycled off.

3 minutes 52

7 minutes 48.5

 

Turned the key on again, pressure shot up to 63 then down to 55 when the pump cycled off.

3 minutes 53.5

5 minutes 51

7 minutes 50

 

At no point did I see or smell any gas leak.

 

I asked my brother to walk back outside later this evening and take a reading for me after a few more hours. Just to see if it holds at 50psi.

 

I was actually kinda hoping for a fuel geyser just so I'd know what the problem was. I did double check for leaks at the schrader and the fuel filter, since those were the only points accessed recently. I did double check for leaks at the fuel tank fittings over the weekend after changing the pump and running the truck for a while.

 

I can run the test again tomorrow, or the next day (mainly just interested in seeing if the quick bleed down behavior in the first test repeats itself).

Any suggestions?

[Jsdirt]

While you have everything apart, it wouldn't hurt to yank the EGR valve and see if it's plugged up with carbon, and stuck open - this will also cause a very rough idle that gets better with RPM.

 

Sounds like the fuel system is ok, although I'd want to replace the spider while it's apart, just to avoid future problems.

 

I think I bought the last one I did on Amazon - was under $300 if I remember right.

[blueridge725]

I took the EGR off over the weekend and it was pretty clean inside. Sure, it was black, but no buildup to speak of.

 

I'm going to clean everything up saturday. Havn't decided whether or not to replace the spider...it is 20 years old after all and I've got it all apart already.

 

Of course, the first alternator lasted 15 years, and I've had 5 since then. I've had 3 or 4 fuel pumps since the original which lasted 15 years as well. Kinda has me doubting replacing an OEM part that ISN"T broke yet. Are the replacements any good? Or will I be doing the job again in 6 months anyway....

 

decisions decisions

[Jsdirt]

I hear you there. Everything seems to be a crapshoot today. Sometimes you get good ones, sometimes junk right out of the box, or fail within 3 months. Better to buy OE branded parts, if possible (Delphi, AC Delco, etc.), but they're not immune from the sea of garbage shipped here from the 3rd world ...

 

The one I bought off Amazon was a Delphi unit. It had wires and a connector on each injector, indicating that they are now electronically controlled instead of the old poppet system. The truck I installed that in sat for 2 years, and was driven occasionally on 6 cylinders, due to a ECM with a V6 program in it (junkyard ripped me off, telling me it came out of a V8), but just this past January, I found a good ECM for it and it's been running better than ever.

 

I'm finding that parts you buy directly from GM are nowhere near the quality of the stuff installed on the assembly line. You'll never get the quality the truck came with. I think this is GM's way of forcing new vehicle sales, instead of EARNING them on merit. For that reason, I avoid buying GM stuff if I can help it.

[blueridge725]

My brother went out to check the fuel pressure at about 9pm (I was working on it around 3pm). It was at 0 psi. turned the key and it went up to 55 then down to 50 in 2-3 minutes and 45 in 8 minutes.

 

Is it possible for the regulator to act up in this manner?

Or maybe the brand new fuel pump is a piece of junk?

 

Not really sure how the system works exactly, so its hard to understand how it might fail...

[Jsdirt]

Most regulators are just a spring and diaphragm system. Springs do wear out, and diaphragms can tear.

 

There should be a check valve in the pump that prevents back flow. Sounds like yours is stuck, or defective. Could also be that the regulator is indeed bad, and allowing pressure to bleed off into the return line. Hard to say over the net. Only way to really know which is which would be to disconnect the return line at some point along its way back to the tank, and leave the end in a container.

 

 

 

Lots of junk out there today in the world of fuel pumps. I recently had a fairly new one in a '93 Volvo 940 that caused the car to die each morning about a mile from the owner's house. Wouldn't restart until it sat a half hour or more, and would croak again and remain a no-start the rest of the day. Ended up being that the check valve was preventing OUTWARD flow instead of back-flow! That was a first for me! You could hear the pump running as clear as day, yet 0 psi.

 

The guy had just spent about $2k on the car trying to fix the problem. It had all the hallmarks of an ignition problem. I initially started troubleshooting the ignition, because I too was convinced the problem was there. Fuel pressure test confirmed the problem - 0 psi when it became a stall and no start.

[Coby7]

Did you do a compression test on this engine?

[blueridge725]

So I stopped by yesterday evening and played with it for a minute. When I cyclede the key, it did about the same as the day before.

 

I took off the fuel pressure regulator so I could see if there was any trash in it, or whatever. Nothing unusual, so I stuck it back on.

 

I then cycled the key again, and the pressure would rapidly jump to 63, drop to 55, then rapidly drop to zero. Over the next dozen or more cycles it did this. Once or twice it would stop at 20 or 35 and hold there, or begin to drop much slower.

 

Of course, when I took off the regulator a decent amount of fuel leaked out. The first couple cycles I thought maybe I just had to 'refill' everything. But after over a dozen, it seems more like I tickled the gremlin.

Finally the pressure dropped to only 49-50 so I left it there. See what it is when I get back.

 

I'm still not pleased that the ACDelco pump runs at 55psi, when everything I see calls for 60 to 65psi. And the pump is brand new (and under warranty). So I think I will swap it out and see if the issue changes. I already paid for it, and its not too hard to do (I have plenty of practice LOL).

 

After that my plan is to switch out the regulator and see if it changes my issue (assuming it still exists). I am going to order the whole spider assembly anyway (I'll just pop off the regulator it comes with and return it as new, so long as I get the same brand for everything it should be fine). The regulator I can just get locally, but the spider is much cheaper ordering online.

 

I want to change the spider to the newer system while I have it open, but I want to change just the regulator first to see the affect on my problem--more for curiosity than anything else. Understanding what's going on may help me in the future, as I have no intention of selling the truck (it has the proper hitch for moving my largest trailer, a reverse fifth wheel setup). Needing this truck as a temporary daily driver was just the impetus to finally work on it. Although we did find a replacement vehicle last night for the wife, which I should complete the purchase of this morning (its hard to find manual tranny vehicles these days!).

 

I would like to change the orings on the gas fittings coming from the tank/pump assembly. Where can I get these? Or find out what size they are? There is a 'rubber and gasket' warehouse around the corner from me if I know the size and type of material. I might can just take the assembly to them, but I prefer to have the info to make it easy on them (especially since they usually just give them to me, as selling some guy 2 orings isn't worth the hassle of the paperwork).

[Jsdirt]

I think your fuel pressure is good. I remember seeing 53 PSI on my buddy's '96 Tahoe, and that one started, ran, and drove, even on 6 cylinders (computer programmed to 4.3 instead of 5.7).

 

Before you spend too much money (I would still replace the spider just for good measure, as these are notoriously failure prone), I'd try blocking off the EGR somehow, just to rule that out. Could drill a couple holes in a piece of metal the right size, cut your own gasket (or use a good RTV, and plenty of it) and seal it up, just to see if there's any change. At least that would rule out the EGR once and for all.

 

No idea off hand what size those o-rings are. I have a kit with just about every size in metric and standard, so if I need one, I just match one up visually and throw it in

[barry G]

the spider is good, the pump is good.

 

in fact, expect 400k miles form the spider stuff.

 

.. there is a way to see vacuum on the obd2 at idle, and/or a good old vac gauge.

these run like an older engine, vacuum is in double digits at idle.

 

read it like testing an old carb engine.

 

..and the relief has to work to return line, of course it is going to drop. you got all kinds of fuel. It would pop something heating up after shutdown otherwise.

 

 

the only rough Idle I ever got was cheap oem plug wires...very elusive.

 

spray some moisture on the wires, coil, even tease the disty cap.

 

having four rear plugs wet and four front dry.. does not even match the timing of the engine. That is a physical misalignment of something.. is the injectors all seated?

 

if it is dumping, go for checking the 1 relief, and not all 8 injectors good for 400k miles.

[Jsdirt]

Maybe ME got all the good spiders - the rest of the country is lucky to get 100k out of one.

[blueridge725]

I havn't had time to work on the truck this week. What I am thinking of doing is putting it back together like it is (albeit with new gaskets). Then I can run it and check the vaccuum, check the plug wires (which were new before parked, but that doesn't rule them out). I can check the EGR, etc.

 

The spider isn't leaking, so I can leave well enough alone. What are your thoughts on the Regulator? The pressure does drop randomly after cycling it a number of times. I understand the fuel can't just keep building up forever, but it seems strange to me that it drops, even to Zero sometimes. I'm leaning towards installing the new one, since there is no way to test just the regulator. I understand that most failures occur with diaphragm, which causes a leak. I have NO leaks. Just thinking perhaps it is failing in a different way.

 

The reason the rear 4 plugs were wet was oil had collected on the intake from the PCV. The intake was wet from the PCV inlet back (the engine is sloped in that direction, for what that's worth). The PCV passes the rattle test, but since its only 4 bucks, was going to just replace it.

 

I can always take it all back apart.

 

Was hoping to put it back together this morning, but the wife wanted to go out, so I am kid-sitting. Where the truck is parked is on a busy street, so I don't dare take the young ones with me when most of my focus would be elsewhere.

 

Did take two cans of carb cleaner and cleaned the oil/gunk off the intake (that thing is actually a silver color, who knew?). Gently washed the spider and plenum with gas.

 

The plenum gasket looks pretty done to me (looks flattened), so I want to replace it.

 

I have a new regulator. so I could put it on and still test the pressure before reassembling to see if it still acts the same. An expensive way to figure out if this behavior with the pressure is normal or not.

 

Unless a part in the pump itself can cause the drop in pressure. Is that what you are referring to as the "relief", barry G?