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Replaced old manifolds on 1990 350 w/ Dynomax Coated headers

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BPatrick

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I removed the old manifolds with sensors in them for a set of headers specific for this year, make, and model (1990 4X4 Blazer w/ 350) with the place for the sensors on the header.

I'm having the exhaust run and put on this weekend but I've started up the truck and drove around a bit with the open headers to see how the lift handles and just cause its fun. I stopped by my friends house to show him the lift and told him how glad I was to have the tbi and then go to start up the truck again. Now every time I start it up it fires up right away no issues...well its not wanting to start. I had to hold my foot down on the accelerator and after a bit of cranking it fired up. Its never done this before. Once it fired up it ran like a champ. Once the truck warms up and I drive it around for a while the check engine light comes on but it still drives like a champ and all the fluids are fine and temp level is perfect. The only thing different I thought it might be old gas so I drove a while and filled w/ 2/3 tank of new gas thinking it might fix it but it still wants to be tough to start and then once it does it runs fine. Sorry for the length but the last thing is that this has happened since I switched out the manifolds for the headers and haven't hooked up any sensors in the header...any suggestions would be helpful.
 
You need any sensors you removed, but should only have been the O2.

Shouldn't affect startup though, nor really how it drives (other than really rich) so make sure your plug wires didn't get burned, and no other wires got pinched/cut on install.
 
dyeager,

thanks for the info...if you said that it would run rich, is it possible that its fowled some plugs?
 
It's possible, I would *think* that with some WOT runs and the engine up to temp, if it was running correctly (IE sensor hooked up), the plugs would probably clean themselves off. If it was burning oil I'd say it's unlikely, but it seems to me you can "burn off" deposits caused by richness.

In any case, if they are good otherwise, you can always take them out and clean them. If the electrodes aren't eroded, and the insulator isn't cracked, there is no reason to throw away perfectly good plugs.
 
I'm still baffled by why I have to hold my foot down on the accelorator and crank for it to turn over. its never done that ever.
 
When you FIRST turn the key to run (not start) do you still hear the fuel pump prime for about 2 seconds?
 
dyeager,

I just got home and I have a few things to do before I go out to the pole barn and give it a shot again but I remember hearing it the last couple of times I tried to start the truck. This was an all the sudden thing. It always started easy and smooth idled down as the truck started to warm up.
 
I had a problem with mine it got bad after I put headers on my old tbi 350. Ended up being the engine temperature sensor in the manifold (not the head) it was stuck in the hot position leaning the engine out so it wouldnt start easily. It finally got to where it wouldnt start at all. Try to hook it up to a scanner and see what the computer is seeing off all the sensors.
 
x2. Autozones (some, all?) will hook a scanner up to your vehicle and see whats going on.
 
Update...now the check engine light doesn't come on hardly at all. If it does...I just turn the truck off and then restart and the light goes off and stays off. I doesn't come on hardly at all. I added fuel injector cleaner and have almost run 2 tanks through the tbi and now it starts a lot easier, like it should. Now, I have a miss and I'm not sure why I'm going to check to see if a wire is arcing or a plug is fouled. This sounds like the nickel and dime thing starting.
 
When the code comes on, check it. Could be bad wire, or component that is failing a functional test by the ECM.
 
Another update...now the check engine light doesn't come on...I think the gas was old and had water or something but now I have a miss....with headers, if something gets to close, i.e. the plug wires, they can burn so I'm going to check and make sure everything is fine and nothing is arcing. Then its spark plug time and sensors and hell I just bought a new truck!
 
Be sure to get that 02 sensor hooked up. It is vital to proper engine performance and gas MPG. It is the main sensor the engine uses to set the air to fuel ratio after the engine warmes up.
Without the 02 sensor the engine just runs on a program stored in the computer This program usually causes it to run rich, poor performance and MPG.
 
Thanks for the tip...I do have the O2 sensor hooked up but it does run rich so that might be what it is. Question for you guys...Lets say I wanted to replace the sensors in the 1990 blazer, how many and what are we talking. Also, I've got a great junkyard around my area and I was thinking of getting some parts...can sensors be reused or go new?
 
Sensors can be reused, problem is that you really have little idea if they are good or bad, if you don't know every other component on the engine works correctly, and you have no way of testing or monitoring their operation.

Almost all of my sensors/injection components are used. Of course, I had a no-start condition that just didn't make sense. Come to find out I had a bunch of bad injectors that were causing the problem.

IMO you are better off buying a scan tool with the money, than simply replacing all of the parts. Something like an autoxray XP240 (old school) would work though.
 
I'm going to look on line for the scan tool as it would be great to have down the road. I was looking up the 02 sensors and the 1 wire is fairly cheap. Now that the exhaust is on, does it really matter what kind of 02 sensor I use ( 1, 2, or 3 wire). I used the correct headers for my blazer from Dynomax and it has the place for the sensor built in. With the 4" lift and larger tires...I like that everything is so easy to get to without crawling underneath it.
 
Scanner would actually tell you if it's fine or not. More than likely it is, it's a simple matter of it getting hot enough to start operating, which is shown by it switching between rich/lean on a scanner.

It's been shown that Delco O2 sensors are better than Bosch, at least for the ones our trucks use, but I've got a Bosch (actually stolen from my car, when I didn't know about Delco being better) on my truck and so far it's worked fine. I wouldn't replace it with anything other than Delco, but that's only when it fails.
 
well now we have it narrowed down to ignition...once I got the exhaust on the truck the service engine soon light quit coming on. I had an exhaust leak when the exhaust got put on and its right by the O2 sensor so now that its fixed it starts and runs well except for a little miss. Cap and rotor time with plugs and wires as they sat for appx. 2 years without much running time and my thoughts are some corrosion. Anyway I've got a couple extra brand new caps and rotors from swap meets and I've got tons of those spark plugs so it will pass some time on a rainy/snowy saturday. I'll let you know how it goes.
 
Update...I was bored tonite and was irritated with the miss, so I decided to change wires plugs cap and rotor. Well as I have the Dynomax headers, boy it creates extra work for changing plugs when compared to manifolds but its worth it because of the sound. Well with the 4" lift and 35" tires I layed under the truck and changed the plugs from the bottom. Well #1 drivers side front is almost impossible to change as the header really gets so tight that I had to pull out some of the Snap-on aviation tools to get to it and bingo, the plug was really corroded. I changed it out and instead of checking the other side, I decided it was fixed as the left side was running cooler and I figured try starting it up and sure enough it is running smoothly...for now. TBI is great when everything runs smooth. Thanks for all the advice guys and tomorrow I'll change out the other side just to be safe...then its drive around in the snow time!
 
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