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Not starting or staying on without gas pedal pressed

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Bjmac911

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Ok...my first post is me begging for help. Hopefully somone here has experienced this issue, got it fixed, and can share with me their thoughts.
Backstory: 1990 blazer, 350, tbi. Bought for my 14 yr old son for us to work on and pass on to him when he's 16 and pays for half of everything.

Problem: when I first bought it a few months back it started right up. Each weekend we'd start it up and take it around the block. Each time we started it, it took longer and longer to turn over and got to the point where it would only start by depressing the has pedal. Now when it starts it shuts off when i take my foot off the gas. Fuel pressure problem? Ignition problem? Both? There is a lot of light gray smoke from the exhaust and heavy fuel smell under the hood.

Solutions: First thing we replaced was the EGR valve after failing emissions- it then passed. Then we did the basic tune up stuff- plugs, wires, cap, and rotor. No improvement. Then we replaced the injectors and fuel pressure regulator- no improvement. So I've spent the entire weekend researching the interwebs and this site. Seems others have had this problem but they never posted what the fix was. Ive also talked to a couple mechanics and followed their advice. Today I replaced the MAP sensor and TPS with no improvement. I got the Ignition Module tested and it passed.

Before I lose more money and patience, i was hoping someone had this same problem and could help. Next options are the IAC, O2, or ECM...HELP!!!
 
Drive it more.

Two things will happen.

1 will be that new and fresh gas will help and wake things up.

The other is that the problem will get worse and make itself more obvious.

First things that I would do besides drive it is trace the vacuum hoses and look for deteriorating hoses. Also check that the hose to that MAP sensor isn't blocked.

Then get back to us.
 
Thanks Justin. I cant drive it cause it will stall when I let off the gas. I checked all vacuum hoses too, forgot to mention that
Fuel filter was also replaced recently as well as the fuel pump...so much has been done I cant remember it all.
 
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The problem with light gray smoke is that it isn't light gray smoke. It is more bluish, or blackish or whitish...each with it's own issue. The plus side is that with the TBI motor, you don't realy need much special stuff to check out codes or sensors. A volt meter and a paperclip can tell you all to need to know.
 
I hooked up to read the codes and only got code 12. I reset the codes by disconnecting the battery and have pulled ECM fuse. No changes to problem or codes.
Smoke would be more white than anything.
 
Loss of coolant into the combustion chamber is white smoke. Head gaskets, cracked heads, even intake gaskets can be responsible. Easy check is to pull the plugs and see if they have a greenish tint to them. Also look into the plug holes and see if there is a clean piston. Steam (from water entry) will clean the carbon off of the piston. Of course milky oil is a serious water contamination issue that would require a full teardown. If you have a cooling system pressure tester you could see if there is combustion pressures entering the cooling system. Anything over 15-16 lbs could be tell-tale, also if pressures increase way before temp increases.
 
It has been a long time, but I think code 12 is a standard code on any pre OBD-II GM not physically running with key on.
 
I am rebuilding my main computer, and typing on this pad SUX!! Got to keep it short.
1 Does the white smoke smell like burning antifreeze?
2 There is a minimum idle speed setting using a screw on the throttle body. Not likely to slip, but something to check. others here can walk you through setting it.
 
Thank you both. Hoping its not the heads obviously but ill check the plugs and holes. Ill also check in to the screw at the TB. No antifreeze smell, just a strong fuel odor under the hood during and after starting the engine. That and having to pump the gas pedal have me stumped...and with that i didnt think the engine was the problem. Yeah, code 12 is just general diag. That made me think maybe the ECM went bad.
 
Clean the throttle body. It doesnt take a lot of buildup for it to stop idling correctly. A can of throttle body cleaner will work wonders.

Also double check the timing, if you bumped it while changing the cap and rotor it could cause all sorts of issues.
 
Worry about sensors or vac leaks before you worry about the heads. A coolant leak wouldn't stop this thing from running or starting.
 
Bjmac911 said:
... No antifreeze smell, just a strong fuel odor under the hood during and after starting the engine. That and having to pump the gas pedal have me stumped...
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I'd check for a cracked rubber fuel hose. The newer gas with ethanol tends to deteriorate the older hoses that weren't designed to handle ethanol. And a fuel injected motor doesn't require pumping the gas pedal at startup.
 
Bjmac911 said:
So...a vacuum hose was disconnected, couldnt find it until today. Also timing was off and low oil pressure. Starts right up and runs good now. Thanks for all the help.
Click to expand...

Not so quick....after this, I took it for a test drive and it up and died on me 2 minutes in. Ended up having it towed to a mechanic who only suggested items be replaced that I already did. It wouldnt start at all now, just crank. Had them reset timing and tow it back home. In other words, it hasnt ran since my last post. Today it would only start, and stay running, by pressing the gas pedal. So, feeling froggy today now that its not 115 degrees out, I figured I'd take apart the throttle body and clean it up. So I disconnected the injectors, then the TPS...then as I disconnected the IACV and it donned on me that part could be the problem. So since the wife is out running errands I asked her to pick it up for me. I go get the keys out of the truck and decide to try cranking it....and guess what?! Focker started right up and stayed running without me pressing on the gas. WTF?!?! Mind you...all of that is disconnected. I turned it off quickly to not do further damage but I'm floored right now. Does this mean it is the IACV? I'll install the new one shortly but figure Id vent and get feedback as I wait for my cute parts delivery person to get here....SMH
 
It could be stuck and not letting air through for a good idle. Which would mean pressing the gas (aka opening the throttle blades) is letting in just enough air to keep it running. It could also be fine, but the wiring to it might be messed up.


I run a FAST EFI set up, kinda similar to a TBI, so the sensors I understand but haven't had any issues that needed this kind of diagnosis. Interesting to say the least.
 
Well that seemed to work. Starts right up and stays on without depressing tge gas pedal. Now it sounds like it wants to stall especially when under load of drive or reverse. Also lots of whitish smoke when pressing on accelerator. Back to more research. Just wanted to update for anyone else having this issue, and open to suggestions for the current issues.
 
I don't know if your engine has a fuel pressure regulator or not,but if it has one,they use a vacuum diaphram to control the fuel pressure to the injectors and if the diaphram in the unit fails,it can let gas get sucked into the intake through the vacuum hose connected to it, and flood the engine,make it run rich,stall at idle,and not want to re-start unless you hold the gas pedal floored..and if it floods badly enough you may have to wait some time for the excess gas to evaporate before it will re start..

I would make sure there are no other vacuum hoses broken or collapsing too,especially the ones for the PCV valve and power brake booster,and the PCV valve itself isn't sticking open or all carboned up..if the EGR valve fails to close all the way it'll act the same as a large vacuum leak also..
 
Thanks diesel. Im in the process now of checking injectors, theyre not spraying correctly. Im also going to rebuild and clean the TB and replace the PCV valve. Dont see any loose or cracked vacuum lines right now. Thanks again for the input
 
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