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.