Getting owned by an 87 TBI

[GetItBilly]

Yup, the TBI (17087020) is appropriate for an 87 Truck. (http://www.carburetion.com/CarbNumbe...umber=17087020). I read around a bunch and 61 lb injectors should be the right ones for 5.7 truck, too.

"Only modifications are the additions of headers WITH no provisions for an O2 sensor and EGR physically disabled as mentioned in post 1" <-- Correct as far as I know, but I have no clue about engine internals.

[jim_in_dorris]

Ok, from the provided prom ID you have a 7747 ecm running $42 mask with a BCC of AFBW. I am more familiar with ASDU and ASDX. I think replacing the injectors is a good start. Without an O2 sensor it is difficult to determine fuelling issues, but old fashioned plug reading can get you close. Your vacuum issue and timing may be the result of a non stock cam wanting timing, you may want to try and see if you can figure that out. Simply checking intake and exhaust lift will tell you if it is stock or not. Not saying that is your problem, but unknown parts make it difficult to know where to look. After replacing the injectors, please look at what the IAC is doing. The counts should be around 10 at idle and go up with throttle position and load. If the truck really wants 6 to 8 degrees of timing, it also needs to be in the bin, or it will just drop those 6 to 8 degrees out of the timing. Taking the map out of the equation means taking engine load out of the equation. You may be fighting a circular problem. Knowing that the cam is or isn't stock will help in determining why it wants timing

[1project2many]

I've got an '87 GMC V2500

Engine is a L05, NA4

Here is the calibration information:

BCC= AFBW3542 Scan id= 4401 Part number= 16073539
Release date= 11/05/86 Engine size= 5.7 Trans Type= Auto trans
ECM/PCM: ECM #01227747
Used in trucks: GMC
Possibly used in:
R20,2WD,3/4 TON R2500,2WD,3/4 TON R30,2WD,1 TON
R3500,2WD,1 TON V20,4WD,3/4 TON V2500,4WD,3/4 TON
V30,4WD,1 TON V3500,4WD,1 TON

Options:
With L05 5.7L GAS 8 CYL (5.7K) V8 TBI
With M40 AUTO 3 SPD TORQUE CONV VAR 1
With NA5 FEDERAL REQUIREMENTS
With NA6 ALTITUDE REQUIREMENTS

[GetItBilly]

I don't want to jinx myself, but let's say the injectors don't help, so then I take the valve cover off, measure rocker lift and find out I have an aftermarket cam? Do I have any options other than tearing the engine apart? Do I need to become really good friends with someone who can burn proms until we find settings that work?

[1project2many]

I think you've described the two options. IMO if you find the cam is not stock it might be cheaper and better to put a stock or very mild "computer compatible" cam back in. But if you happen to make friends with a guy that can burn proms, well, even a stock engine can benefit from tuning.

[vilefly]

Sorry for interjecting, but this one is a classic case of fuel starvation. The injector acid test for us in the field is to disconnect one injector while it is running, and see if it will still struggle on and stay alive or instantly die completely no matter what is done with the throttle. If it dies, the injector is not flowing enough. Ran across this situation alot with cadillacs and gm trucks.

I skimmed the posts, and did not see any fuel pressure readings while the throttle was gunned. If the 9-15psi fuel pressure does not drop at all, then go for the injectors. If it does drop at all, look to the fuel pump/kinked fuel lines.
You may want to get an adjustable fuel pressure regulator in case of a cam scenario. The big block 366 engine uses a 23 psi regulator with the same injectors, BTW. Yup, they cheated.

Oh, just one more thing. Make sure your harmonic balancer reads true TDC. The outer ring has been known to "walk" over time. The other scenario happens when harmonic balancers were swapped from different motors. Doubt it is a timing issue, but it never hurts to check.

[GetItBilly]

It had the wrong injectors! Got new 61 lb injectors installed and the top end of the TBI rebuilt. I could immediately see a huge difference in the size of the spray pattern coming out of the new injectors compared to the old ones. It's 40 degrees out today...the first time I fired it up with the new injectors it came right down to idle @ 600rpm after a couple minutes. Timing checked out at about 2 degrees, which is where I wanted it, and holds nice and steady now. Did the IAC relearn, too. Haven't driven it yet, need to run to the store to get a couple things to finish up an oil change.