Tbi swap build thread

[pancake]

Hello again,

I finially had the time to re-install my old intake and put the TBI onto it using an adapter plate.

I got the truck started but it is ideling very high about 1900rpm and has a VERY loud whistling sound to it. I let it run for 5 min or so and it did not stop whistling. It is almost unbearable. If you remember from my other posts I eleminated the EGR. Does this have something to do with it?

I thought the whistling was coming from the IAC so I replaced it. no change.

The truck will also act like the idle is going to come down but then back fires through the TBI.

The truck starts fine but won't idle below 1800rpm unless I turn the dizzy to adjust the timing but then it backfires and dies. I can not get the idle low enough to use a timing light but I rechecked the rotor position in relation to TDC of #1 and I am close to "0" degrees timing.

I did not have this idle or LOUD whistling issue with the OEM manifold and EGR valve, but the truck would not idle correctly and would backfire out the exauet with it on. That is why I put my old intake "Edelbrock 2101" back on.

I did install a fuel pressure gauge and ran 3/8 allumminium? tubbing from the tank. The fuel pressure is only at ~ 6psi by the TBI. could this be the problem? The TBI is spraying a nice steady mist when the truck is running.

I found a post by RF on IAC adjustment....do I need to do this?

The truck did not have these issues with old OEM intake and EGR, I know I installed the new intake correctly and do not beleive that I have a massive vacume leak causing the LOUD whistling. I am at a dead end and any help would be greatly appreciated...Thank again, Pancake

[rfmaster]

Originally Posted by pancake

Hello again,

I finially had the time to re-install my old intake and put the TBI onto it using an adapter plate.

I got the truck started but it is ideling very high about 1900rpm and has a VERY loud whistling sound to it. I let it run for 5 min or so and it did not stop whistling. It is almost unbearable. If you remember from my other posts I eleminated the EGR. Does this have something to do with it?

I thought the whistling was coming from the IAC so I replaced it. no change.

The truck will also act like the idle is going to come down but then back fires through the TBI.

The truck starts fine but won't idle below 1800rpm unless I turn the dizzy to adjust the timing but then it backfires and dies. I can not get the idle low enough to use a timing light but I rechecked the rotor position in relation to TDC of #1 and I am close to "0" degrees timing.

I did not have this idle or LOUD whistling issue with the OEM manifold and EGR valve, but the truck would not idle correctly and would backfire out the exauet with it on. That is why I put my old intake "Edelbrock 2101" back on.

I did install a fuel pressure gauge and ran 3/8 allumminium? tubbing from the tank. The fuel pressure is only at ~ 6psi by the TBI. could this be the problem? The TBI is spraying a nice steady mist when the truck is running.

I found a post by RF on IAC adjustment....do I need to do this?

The truck did not have these issues with old OEM intake and EGR, I know I installed the new intake correctly and do not beleive that I have a massive vacume leak causing the LOUD whistling. I am at a dead end and any help would be greatly appreciated...Thank again, Pancake

Hmmm. My got feel tells me that you have several problems conspiring against you.

Idle at 1900 is not a good thing - you have a vacuum leak. Check TB to intake manifold gasket - there are different gaskets out there. Some seal better that others. Make sure that throttle plates are fully closed. I have seen post where throttle cable is too short and keeps throttle plates partially open!

YOU MUST RESET IAC - no if buts or whatever. This must be done as ECM has no idea where IAC is positioned, but if it was set to a known position it can make adjustments to adjust idle.

6 PSI is too low - it maybe enough for idle, but ECM VE calibration tables are setup for two injectors (62 lb/h) operating at 13 PSI. Injector delivery rate changes non-linearly with fuel pressure. Popping though TB is an indication that engine is running lean (or timing is way to advanced)! You need 3/8" supply line - soft steel or aluminum with a fuel pump rated at least 20 PSI and capable of moving 40GPH (aka GSL393, Carter P5001, others). Do you have carb rated pump by any chance??? 6 PSI is a carburetor rated working fuel pressure. Cheap fuel pressure gauges are also known to give false readings. (I had good luck with Summit SUM-800130 as it tracks within 2 PSI window of Auto Meter 2239). What is is the supply voltage at fuel pump - it better be around 12volts!

EGR - re verify that you do not have vacuum leak under block off plate!!

Take couple hi res photos (if you can) of your engine bay around TB and lets see if we can spot the obvious.

//RF

[68 TT]

The guys on the DIY EFI GM ECM list have had several different aftermarket TBI adapters leak at bolt points. Some went so far as to fill the bolt head areas with epoxy so the TB wouldn't leak.

Did you make your adapter or is it an aftermarket one?

[68 TT]

Originally Posted by pancake

Hello again,

I finially had the time to re-install my old intake and put the TBI onto it using an adapter plate.

I got the truck started but it is ideling very high about 1900rpm and has a VERY loud whistling sound to it. I let it run for 5 min or so and it did not stop whistling. It is almost unbearable. If you remember from my other posts I eleminated the EGR. Does this have something to do with it?

I thought the whistling was coming from the IAC so I replaced it. no change.

The truck will also act like the idle is going to come down but then back fires through the TBI.

The truck starts fine but won't idle below 1800rpm unless I turn the dizzy to adjust the timing but then it backfires and dies. I can not get the idle low enough to use a timing light but I rechecked the rotor position in relation to TDC of #1 and I am close to "0" degrees timing.

I did not have this idle or LOUD whistling issue with the OEM manifold and EGR valve, but the truck would not idle correctly and would backfire out the exauet with it on. That is why I put my old intake "Edelbrock 2101" back on.

I did install a fuel pressure gauge and ran 3/8 allumminium? tubbing from the tank. The fuel pressure is only at ~ 6psi by the TBI. could this be the problem? The TBI is spraying a nice steady mist when the truck is running.

I found a post by RF on IAC adjustment....do I need to do this?

The truck did not have these issues with old OEM intake and EGR, I know I installed the new intake correctly and do not beleive that I have a massive vacume leak causing the LOUD whistling. I am at a dead end and any help would be greatly appreciated...Thank again, Pancake

My 90 Z71 with the 5.7 TBI made a pretty loud whistle / sucking sound at idle when the air cleaner was off and only slightly muffled when the lid was flipped. With the air cleaner assembled like from the factory it all but disappeared.

If you have more than about 4 degrees advance and less than about 30 it should only pop or backfire if the plug wires are grounding out or connected wrong. Check the routing and condition of your plug wires after seeing what amount of initial advance you have. Your engine might like more advance too. My Camaro will start to pop & miss with less than 8 degrees advance due to the cam profile and compression.