Dry Start Only When Engine Warm 1996 Suburban

Maintenance/Repairs
,
1

My Burb starts right up when the engine compartment is cold. Can barely touch the key and the thing fires right up.

Once engine compartment is hot (operating temp), I shut off the motor, let it sit for a few minutes and I get about 3-5 seconds of dry start each time I start it. It fires right up, runs great after that dry start period.

The dry-start behaves as if it’s starved for fuel for those 3-5 seconds.

It’s a K1500 with a stock 5.7l (350 ci). 180,000 miles and the entire drivetrain runs like a top. Only mod I’ve made is a K&N cold air intake.

Here’s what I’ve done/changed recently (i.e. within the past 5k miles):

Fuel pump, OEM installed by dealer.
Fuel filter.
Ignition control module, BWD.
Ignition coil, BWD.
Crankshaft position sensor, GM OEM.
Engine coolant temp sensor, BWD.
Oxygen sensors (all four), GM OEM.
Catalytic converter, replaced one of the two.
Plug wires, BWD.
Plugs, Delco OEM.
Distributor cap and rotor, BWD.
Cleaned ground connection (bolts to frame) for fuel pump.
Alternator, new not reman.
PCV valve.
Battery.

Full diagnostics by a very qualified shop two weeks ago, no bleedback from injector spider, fuel pressure solid and holds perfectly. After 90 minutes of troubleshooting, the mechanics finally gave up.

One last thing with potential that I can think of is that I started running ethanol-free gas around the same time this issue surfaced. Not at the exact time, but at a relatively similar time. Gas mileage has increased by 40% and power increased, hard to blame “bad gas.”

2

Make sure the fuel line is not too close to exhaust and engine block. Fuel pump suspect 2. Try a shot of starting fluid next failure mode to confirm fuel issue. I hate to recommend a relearning for the engine as other problems may surface, but to start the brains over requires a battery disconnect. Turn off air and all heat functions first!

3

It could be quite a few things. I’m assuming there is no check engine light on. I’ll give it a guess.

I suspect it isn’t fuel starved, but in fact there is too much fuel on hot starts. Cold engines require a rich fuel mixture to start right up. Hot engines need a much leaner mixture, otherwise they won’t start until enough air gets sucked into the intake manifold during the cranking process to lean the mixture out. I think your engine is getting flooded with too much gas on hot starts.

I’m not experienced on your make/model, but fuel injected cars – which I assume yours is – usually use a “cold start valve” to inject extra gasoline on cranking. There’s just one cold start valve, which injects into the intake manifold. But, to prevent flooding, the cold start valve is only – or only should be – actuated on cold starts. The way it usually works, there’s some method – often a timer, controlled by the engine coolant temperature – which measures-out the amount of fuel injected by the cold start valve. When the engine coolant is cold, it injects a lot. As the coolant temp increases, the amount of gas injected decreases, until at some point when the engine is at full operating temp, no gas at all should be injected by the cold-start injector on cranking.

My guess is that there is something wrong with either your cold start injector or the gadget which measures out how much gas it is supposed to inject.

One way to test this might be to press your foot to the floor to hold the throttle wide open when you crank it while hot. If it starts more easily with the throttle wide open, that means indeed it needs a leaner mixture, and there may well be something wrong with the cold-start mechanism.

4

Did you replace all those parts in an attempt to cure this problem?? It’s a 16 year old truck with 180K miles on it…Be thankful it starts at all…

5

Barkydog and GeorgeSanJose, thanks for chiming in to offer suggestions.

Barkydog, the fuel line is as close to engine and exhaust as it has been since it was new, but this is a problem that developed in the past couple months. I am fairly ignorant of gasoline, but your comment kind of makes me wonder if the eth-free gas I switched to might be causing it. Perhaps something about the formulation that causes it to give the dry-start symptoms that I never got running gas with ethanol in it. I have no idea, but I hadn’t even thought of something so simple as running some gas with ethanol in it to test it. Fuel pump is going great. The shop that did the diagnostics for me tested it with the engine cooled off and then again when engine compartment was hot. They couldn’t find anything wrong with it, or anything else. I really appreciate you pitching in. If you’ve got any other thoughts/ideas, please don’t hesitate.

GeorgeSanJose, I had ruled out too much fuel as the culprit because I’ve watched it fire after the dry start and there aren’t any puffs at all coming out of the tail pipe. I expected to see at least a little puff of black as it gagged down extra fuel, but nothing. But your idea makes sense. I’ll dig through the service manual and see if I can locate any components that do what you describe. I appreciate your help a bunch. Without it I wouldn’t have even thought to look for this. Should any other ideas strike you, I’m all ears.

I’ll post what I find to hopefully help the next person.

Have a great night.

6

Next time you try a hot re-start hold the accelerator down half way to the floor when you engage the starter.

7

It could just as easily be a “Wet Start”…leaky injectors…

Try this…Crank it for a few seconds, then turn the key off…Try again. Does it fire right up the second try? Why? Who knows…Drive on…

8

To Burb Bum. I had exact same problem with my '95 Caprice. A friend told me to try this. Turn ignition on, wait for fuel pump to to click off. Should be able to hear it. Turn off all accessories so you can hear the pump. If you still cannot hear, ( background noise ), just count to 3 or 4. then engage the starter. Worked for me. If you already tried this & still no fix, sorry. It is all I got. By the way, Barkydog is wrong about using starting fluid! Bad idea for an engine that “WILL START & RUNS WELL!”

9

“I shut off the motor, let it sit for a few minutes and I get about 3-5 seconds of dry start each time I start it.” The fuel pump is a good idea, but I would think it would exhibit the behavior more when cold than warm. The use of starting fluid in a no start condition is to confirm it is a fuel problem. An exhaust manifold leak boiling the gas in the line was one possibility I was considering.

10

If the fuel pressure reads 63 PSI or more and is steady then the problem might be with the popet valves on the spider assembly. The popet valves are the mechanical fuel injectors on the spider assembly which uses the fuel pressure to blow them open to inject fuel into the engine. If the popet valves develope gum and varnish on them this can cause them to stick as the engine heats up. You might try adding a fuel system cleaner to the gas tank to see if gum and varnish are effecting the popet valves on the spider assembly.

Tester

11

Wow, thanks for the ideas.

I forgot…when I initially tried to post this issue, there was some kind of error that kept popping up. I shortened it up about five sentences of further info and it posted.

Barkydog, don’t worry about it. I understood why you suggested the starting fluid. It’s a good suggestion. But I guess you can’t always trust that someone you suggest this to won’t just keep spraying it into the intake. Hard to guard against stupid. Anyway, I understood what you intended with the idea. Thanks for offering it. As far as an exhaust manifold leak, I’ve never heard or smelled anything underneath it to suggest there is one. But it does remind me of a very short-lived vapor lock like with carbs at altitude, except that it does start up and run just fine once it does start.

Tester, thanks for the help. Some of the info I deleted to get the posting to actually post is that in the past couple months, I’ve run a tank with Techron cleaner added, two tanks with Lucas fuel system cleaner added and have noticed no change at all. I know the Lucas is a pretty mild cleaner, but I would think the Techron would have cleaned it out. But maybe not. I’m certainly no expert on fuel additives. In your opinion, should I try a different fuel system cleaner or do you think the Techron and Lucas would have removed the problem if that was it?

Cruser, thanks for the tip. I used to be a farmer and we pretty much only had diesel everything. It became a habit to never just crank a key, but to turn the ignition system on and wait a bit before actually cranking it. As such, my fuel line and injectors are always charged, every time I start the Burb. I know there aren’t any glow plugs, but I do it anyway, if for no other reason than to take myself back to when my life was farming. Good suggestion, though.

Rod Knox, thanks to you as well. So with the accelerator pedal halfway down, is it going to dump more fuel into the intake or is this to prevent something else from telling it to dump more fuel in right away? Just curious what the result might tell me. Do you suspect too much or too little fuel or something else? I’ll give this a shot tomorrow and see what happens.

GeorgeSanJose, I combed through the service manual last night for quite a while, which is about as straightforward as trying to find part numbers for Chevy/GM products. What is it with these guys? Like all the part numbers are top-secret and you have have some special training to understand the logic or lack of it in the layout of the service manuals. 1,500 pages with a two-page index. I didn’t have but a few minutes. I’ll look over the intake more closely tomorrow.

Thanks, folks.

12

GeorgeSanJose, I forgot to mention…the service engine light came on once a couple months ago. I forgot the number, but it was for a short across or bad ground on ICM. I put a new ICM in it and the service engine light shut off and no other codes have been stored since, which is a little baffling to me because it has been my understanding that the OBDs were still coded to throw a service engine light for nearly every hiccup, that GM turned them down a few notches some time after the '96 model to keep them from storing codes so frequently. Mine has thrown a code only for that ICM issue and some tanked O2 sensors (many months prior to the ICM issue) in the two years I’ve owned it. Another piece of info I deleted to try to get the question to post. I overlooked offering that in my first reply to you.

13

Not sure if this was sill used on the 96 Chevy trucks and Suburban. I know in 88 they use an oil presser switch that turned off the fuel pump if the oil presser went to low. I have seen this malfunction and cause hot and cold start problems. If this the problem,it may start to take longer to crank it before it starts.

14

Re stepping on accelerator. The engine must have sufficient air to start and the idle air control valve and throttle may be partially restricted with sludge and varnish, reducing the air supply. At cold start up the idle air control valve opens wide enough to rev the engine beyond 2,000 rpm, sufficient air to let the engine start up. At a hot restart that valve is nearly closed. If pressing the accelerator enables starting clean the throttle and IAC valve and ports.

15

oldbodyman, thanks for chiming in. Good heavens. It’s Pandora’s Box. I’ll keep this in mind. Thanks.

Rod Knox, I did five starts at op temp with the accelerator depressed about halfway over the course of the day. The first three, my Burb had sat for only a couple minutes before I restarted it. She started right up, but I’m hesitant to count these three only because I didn’t give it the 10 minutes to sit before restart, which is where I get that dry-start. I did get a chance to do two other starts with 10 minutes of downtime after I shut it off. With the accelerator depressed halfway, I still got the same dry start symptoms. That’s really only two times so maybe it’s telling, maybe it’s not. I will do it some more tomorrow and see if it still doesn’t change anything. I appreciate your explanation of the rabbit you were chasing.

16

Hey Rod Knox, you seem to be fairly familiar with this stuff. Random question for you. Because the problem surfaces when the engine compartment is at operating temp, could it be a problem of too much resistance inside the circuit of the IAC or throttle position sensor? This doesn’t, by any chance, mimic symptoms that could come from a bad EGR valve, does it? I’ve never had to change an EGR on a vehicle so I don’t know if this would fall into symptoms associated with its failure.

oldbodyman, it’s that hunch that this is a problem that’s going to get progressively worse until it just won’t start or stops running, probably out on the Interstate in rush-hour traffic when it’s 100-degrees and all the kids are in the Burb with me, that has made me determined to figure out what’s failing. So I appreciate you chiming in.

17

Another possible piece of the problem is heavy carbon buildup on the intake valve stem. The carbon will absorb fuel until it becomes saturated and then fuel passes but through a somewhat obstructed port. When cold the injectors are pushing a great deal of fuel into the engine to get it started and the carbon gets quickly saturated.

But, like many annoying symptoms, yours might be the result of several minor problems whose combined effect is a PITA. Weak spark requires a richer mixture. Winter fuels may be vaporizing too easily in the hot engine. Somewhere I have an old trouble shooting manual that must have 30 pages of diagnosis for your problem.

18

It’s hard to say. This could shut you down if it thinks you have no oil presser. The same could be true when you go to start it, it may just not start. The problem as I recall with this sensor when it failed the oil presser had rise as you crank it to turn on the fuel pump. In your case the truck is up to temp. So it cranks and the oil presser come up,fuel turns on and truck starts. Normally its time delayed. IE lets truck start then reads oil presser.
Please let us know what you find.

19

@Burb Bum, you are right, when there is too much fuel on hot start you’ll usually hear that “spitting” sound as it starts-up, that sound sort of like a person makes if they swallow a bee by accident. “spppppt, sppppt, spppt,” then it fires up.

If you aren’t hearing that, then too much gas isn’t likely the cause. And it doesn’t sound like the check-engine codes you had before are related to the current problem.

You are absolutely right about service manuals. Sometimes I think these manuals are written by chimpanzees! These manuals can make something as simple as “turn the bolt clockwise 1/2 turn” to be about as understandable as quantum mechanics! Maybe these shop manuals are some kind of inside joke or something on the layman. A single topic can be spread around 5 or 6 different sections of the book, and there is no clear way to know even if you’ve found all the places that topic is discussed. And I’ve seen things so unbelievable in service manuals that if I claimed I was abducted by aliens, that would be more believeable than what the service manual says. And then there’s the problem where the manual will describe the wierd part that might be the cause of the problem by one name in the body of the text, but in the diagram it will have a completely different name! You have no clue if the text or the diagram are even related. And what about when the manual lists the procedure step by step, but omits some important part, like you have to remove the engine first if you have air conditioning? lol … One day if I remember I’ll post an example direct from a shop manual about how the manual says to get the check engine codes spit out of a 1990’s Toyota Corolla with manual transmission. It’s a hoot.

20

Hey folks,

Thanks so much for your help with this. I was getting fatigued talking to myself under the hood so it’s nice to have a couple other minds chewing on it. Even if it doesn’t get solved here, it is with gratitude that I read each of your suggestions and ideas.

First, a quick summary of what I messed with today and what I got as a result. This morning, I did two restarts at operating temp, each with a waiting period of 10-15 minutes after initial shutoff (ie. after I had driven somewhere and shut it off). I did it with the accelerator pedal halfway down each time and zero delay. She fired right up.

I stopped by a parts house on the way home and grabbed some Mystery Oil, figuring I’d at least get a decent cleaner headed through the fuel path. Maybe it helps, maybe it doesn’t, but it may as well be running through there while I’m trying to get to the bottom of it. Worst case, it cleans out some varnish in the injectors. Best case, that was my problem to begin with.

While at the parts house, the guy who helped me said he has a similar era Chevy that had developed the same, as he called it, a “lean start.” He swapped out the engine coolant temp sensor, which I have already done, and the air temp sensor that goes in the air intake. He said he didn’t know which one solved the problem because he swapped them both out at the same time. And he’s never seen the symptoms return.

The one in the air intake was 1996 vintage so I swapped it out for a new BWD. Then I warmed it up to op temp in the driveway for about 20 minutes, shut it off, let it sit 15 minutes. It started right up without touching the accelerator.

I had to run to the store. I shut it off, was in the store for right at 10 minutes, came back and she fired right up without touching the accelerator.

It has been probably three months now since my Burb fired up immediately at operating temp. It just did it twice in a row after changing out that air intake temp sensor. Maybe that was the issue. Maybe not. I can’t imagine that Mystery Oil could have affected a change so quickly, but I guess it’s possible. I don’t know.

I’m going to see what happens tomorrow. I’m hoping the symptoms are completely gone, but it has been such a pest to root out that I’m skeptical. I’ll be surprised if the dry-start issue just disappears and hope to be surprised. I’ll post what happens this weekend while I’m out driving around.

Rod Knox, would Mystery Oil (or some other cleaner) eventually remove carbon if it were on the intake valve stem? By “eventually,” I mean like in a few tanks of running it, not over the next decade it would eventually erode the carbon. Or at this point, as dirty as the injectors could be, is getting the injectors cleaned out by a shop sort of in order? As far as winter fuels go, I’ve been running ethanol-free for about the past 3-5k miles so fuel vaporzing shouldn’t be an issue, should it? Serious question, not being sarcastic.

oldbodyman, I spent more time combing through the service manuals last night. Found the oil pressure sensor. In the manual, it looked fairly open to get to. Under the hood, it looks like it’s sort of buried beneath a couple AC lines, which is a handy location. I’m hoping that’s not it, but until I can see if the intake sensor actually fixed the issue, your idea is still on the radar.

GeorgeSanJose, yes, there is none of that spitting. No puff of smoke, no spitting. And your comments on the manuals are true. No single section provides complete information. The GM manual parks all kinds of stuff under the chapter “On-Vehicle Maintenance/Repair,” where it offers snippets of clues that you need to make sense of the other pieces in other chapters when you can find them. I’ve had one Honda. I bought an OEM service manual for it on CD and it was absolutely intuitive and helpful. I could find and understand everything in it in a matter of minutes. And it was half the number of pages, but told me in perfect detail with very helpful drawings (that matched the steps, unlike GM’s) every single step I needed to make any repair to it. It takes me longer to locate everything in a GM service manual than it did for me to locate and finish the repairs on my Honda. I can’t even wrap my brain around the way GM does business. 15 years ago I promised myself I’d never buy another Chevy. As much as we love the utility of our Burb for our family, I’m being reminded why I promised myself that.

Thanks so much to each of you. I’ll run it around this weekend and see what happens and return with whether the issue is gone. I greatly appreciate each of you chiming in to help. Have a great evening.