400 cid into '91 Gmc

[chuckander]

Hello,

I recently transplanted a 400 sbc with a set of preinjection 350 sbc heads (I already had them on in an older pickup) with an edlebrock airgap manifold. To get the stock TBI to mount I had to use an adapter for the bbc on top of an adapter to mount it to the manifold. I reused all the original TBI components. The problems I'm having is when it starts to warm up it starts to surge and under a load it surges bad enough to almost die. After warming up it won't idle and dies when in gear and not currently applying the throttle. Another problem it is having is it is causing serious blow-by into the crank case but when the spark plugs are pulled they are white like it is running too lean. I've checked and replaced all the vaccum lines and replaced the TPS, MAP, and IAS. The original manifold was an EGR manifold and the edlebrock isn't. I never heard the original engine run because it was blown. Do I have too much manifold for that system? Or is something else the issue. Thanks.
Sincerely,
Chuck

[Fast355]

Hello,

I recently transplanted a 400 sbc with a set of preinjection 350 sbc heads (I already had them on in an older pickup) with an edlebrock airgap manifold. To get the stock TBI to mount I had to use an adapter for the bbc on top of an adapter to mount it to the manifold. I reused all the original TBI components. The problems I'm having is when it starts to warm up it starts to surge and under a load it surges bad enough to almost die. After warming up it won't idle and dies when in gear and not currently applying the throttle. Another problem it is having is it is causing serious blow-by into the crank case but when the spark plugs are pulled they are white like it is running too lean. I've checked and replaced all the vaccum lines and replaced the TPS, MAP, and IAS. The original manifold was an EGR manifold and the edlebrock isn't. I never heard the original engine run because it was blown. Do I have too much manifold for that system? Or is something else the issue. Thanks.
Sincerely,
Chuck

Chuck,

An injection system is not going to cause crankcase blowby, but poor ring seal or a plugged PCV system will.

As far as your issue goes I see multiple problems.

You say it has a set of smog 350 heads on it. I take that to mean that it has a set of 882/993/624 equivalent slow burning 76cc chambers. The TBI factory spark map will be inadequate for these heads and the intake manifold will create the need for major fueling changes. The TBI heads were designed to require less spark advance and the intake swirl allowed the engineers to stay leaner.

Unless you have your EGR disabled in the PROM chip your fueling and timing will be even further off. The ECM will be advancing the timing and reducing the fuel in anticpiation of the EGR operation.

I helped build and install a 406 into a 1990 G30 based motorhome years back. It was a stock rebuild on the 400 with the exception of 5.7" rods, a 204/214 "RV" cam, and "810" casting 64cc TBI heads. We used a 3704 edelbrock TBI performer intake and a TBI setup from the vans stock 350. It ran very well on the stock chip with the fuel pressure bumped to around 15 psi.

Chris

[EagleMark]

Adding to Fasts post. All your symptoms are not surprising me for a transplanted TBI system and a stock chip. Then add an intake manifold that is rated from 1500 to 6500 RPM, so it does not help with any issue under 1500 RPM...

What is the fuel pressure?

What TBI? SBC, BBC and what injectors?

You did not mention the cam specs either?

Did you hook up the Park/Neutral wire to ECM so it knows if it is in gear?

VSS is another sensor that is often overlooked but can be a great help on idle. Some ECM can get by fairly well without VSS, while others can not.

What ECM and what chip BCC (four letter code) do you have?

All these things are important and can cause the issues your having... except the blow by. There's no way for TBI EFI to cause that.

Then the next step is your going to need to at least see data and read codes, for putting together a custom tune chip you'll need ability to save the data log. Without us being able to see what is happening is just educated and experianced, steps or guess to what is happening.

[chuckander]

The fuel pressure sits between 12 to 14 psi. I did no modifications in anyway to anything As far as the cam specs all i can say is it was an overhauled (not rebuilt) short block so the cam was new but is a factory spec cam for a '77 400. As far as the blow by could it be a bad manifold gasket? The motor had sat for almost a year before installing.

[buddrow]

The fuel pressure sits between 12 to 14 psi. I did no modifications in anyway to anything As far as the cam specs all i can say is it was an overhauled (not rebuilt) short block so the cam was new but is a factory spec cam for a '77 400. As far as the blow by could it be a bad manifold gasket? The motor had sat for almost a year before installing.

To reinforce Fast and Marks earlier statements, the blow-by is likely cause by work oil control rings which will 1. Contaminate your intakr charge, 2. Can cause a loss of compression, 3. It is a mechanical issue which you will never "tune out". The intake manifold will not cause blow-by it will only leak coolant or "vacuum". Now, be sure that blow-by is what you're experiencing. When u pull the pcv valve from the valve cover and place you hand over the hole do you feel air pressure blowing against your hand? That is the semi-compressed air blowing past the rings and out that hole. If you have smoke coming from the tailpipe that could be several different issues.

[chuckander]

I used a compression gauge and all cylinders sit between 148 to 150psi. I then checked the pcv and no pressure. As far as the blow by I was informed if it did get into the cylinder and down passed the rings it would have almost a propane smell. It does smell like raw gas. That's why I asked about a bad intake gasket. And there is no smoke from the tail pipe. Also forgot to answer from earlier it's a half ton pickup that had a sbc 350.

[buddrow]

Ok so why do you think you have a blow-by condition? If there is no air being pushed out the pcv hole then its not blow by. Is the pcv vavle wet with oil? Are your valve covers baffled? Rereading your original post, plugs are white? Its lean which will also cause the surging and other issues. You need a new tune. Maybe a large vacuum leak at the intake manifold? This situation falls into the the " call the doctor, hey doc i have a rash what do you think it is" catagory. Impossible to know for sure without some data or the vehicle in front of me.

[chuckander]

The blowby condition I was asking about was excess fuel blowing by the rings because the oil in the crank case smelled like raw gas and that the plugs were white like it was running lean. That is what was really confusing. That's why I asked if it could be a bad intake gasket. Would that cause a big enough vacuum leak to cause the surging, lean fueling, and raw unburnt fuel getting into the oil? No, the valve covers aren't baffled.

[buddrow]

An intake gasket leak can cause lean surging. Any fuel in the oil is excessive but will generally cause the plug to at least be wet and discolored if not covered in black soot. It may be leaking fuel when engine off and contaminating the crankcase. The surging is likely a lean condition, you just have to find the cause whether its the tune due to the engine combo or if its a mechanical issue. Take a sample of your oil and see if it ignites when exposed to flame or spark.

[chuckander]

I will check the oil when I get home.I Would I be better off reusing the tbi heads and manifold off the bad motor since I had them checked at a machine shop and they were still in good shape. I simply tried this one because it was already all together. The only thing I have to do with the tbi heads are drill the extra coolant hols for the 400.

[chuckander]

I drained the oil from the engine. There was no antifreeze or water in it and it was still very clean and clear, but it when I took a small amout and held a lighter to it, it caught on fire and burned steady for about a minute until I poured some baking soda on it. Yes I did it outside so catching anything on fire would be slim.

[buddrow]

Sounds like a fuel contamination issue. Now to find out where the excess fuel is coming from. Leaking injector and/or injector pod? I wouldn't change anything(heads, intake, etc...) just yet until you find how the fuel is getting into the crankcase. Obvious place of origin is the injector setup so focus on that initially and go from there. I assume you are not using a mechanical fuel pump so we can rule that out. Check for fuel dripping from the injectors after engine shutdown. Check for porosity in the tbi housing or possible modifications made to the throttle body has created a leak in the housing? All things to consider and inspect.

Buddrow

[chuckander]

I checked the tbi and gaskets before draining the oil and there was no signs of any leaks and I didn't start the engine but I truned the key on and pressured up the fuel system. There where no leaks there either

[buddrow]

Hmm. Fill it with new oil and see how it goes. The fuel has to be getting in there somehow so I'm still curious as to how.

[chuckander]

Put 6 quarts of new oil in( extra quart for the factory oil cooler) and replaced the filter. Run it for about 10 min. When it started to surge again. Shut it down and checked the oil. Can smell raw gas again. Checked oillevel before starting, immediately after shutting off, and then again 10 min. Later.