autobahn_clem

Hello all,
I transplanted my an LT1 into my '84 GMC 1/2 ton, this engine ran fine when pulled, now after install, it starts runs great for about 5 min. then it begins to act as if it were running on 6 cylinders; BUT now and then when i play with the accelerator it's as if the problem goes away and all the power is back. Now, i have replaced the cap and rotor, plugs and wires before i installed it into my truck; however, it ran strangely, what i mean is that motor ran fine, but the transmission would not shift properly, and my "service engine" light was on... other than that, it ran fine but then i found a blown fuse, this is a 15amp (EMI) fuse that controls the "Mass Air Flow Sensor, Secondary Air Pump Relay, EGR Solenoid, Evaporative Emission Solenoid, O2 Sensor, Automatic Transmission"... Now, obviously this is why the transmission was not shifting properly, but now i have the poor idle issue after replacing the fuse (btw, it blows after a while). HELP!!!!!!!! thanks all.

autobahn_clem

BTW, i have to keep all the emissions stuff, we have testing here.

dhdenney

iTrader: (53)

Did the light go out after replacing the fuse?

dhdenney

iTrader: (53)

BTW, I am not real sure which fuse you are referring to. ???

FAD2BLK93

Have it scanned to see what the codes are...and check the voltage output of the TPS sensor.

autobahn_clem

Yes, the light did go out after i replaced the fuse... I am poor-boying it, so i have not had it scanned.
The EMI fuse that is located in the external (under hood) fuse box where the fan relays are located, at least on the buick roadmaster.
You think the TPS would cause this to spudder and act as if it were missing?? Remember, this thing will do this and then out of the blue, all the power is there for a few seconds, and then back to same old thing... frustrating.

Thanks guys!

dhdenney

iTrader: (53)

I looked and at least in the F body, all I can see out of what you mentioned is a fuse for the AIR pump and it's a 20A. Buff and Caprice might be able to shed some light here. But yes the TPS can monkey with your performance cuz it's the throttle position sensor. If it can't monitor that, then it can mess with stuff. Output should be .55 volts at idle.

autobahn_clem

Okay, just returned from diagnostic and found the following:
11- Malf. indicator lamp (i understand all the "lamp" codes; using VDO gauges)
15- Coolant temp signal high or open
24- Vehicle Speed Sensor low output signal (this may be caused by VDO gauge)
26- Evap. purg. control circuit
27- EGR Electronic Fault
29- Secondary Air injection pump circuit
48- Mass Air flow syst. failure
64- RT O2 Sensor to rich
65- RT O2 Sensor to lean
77- Fan 1 fault
78- Fan 2 fault
81- Shift Solonoid B circuit
82- Shift Solonoid A circuit
83- Torque converter quad mod.
84- Downshift feedback
90- TCC enable fault (QDM)
96- Oil Level light fault
95- Oil life light fault

Now, he did reset the ECU, and i will return some other time to re-read any faults. However, the same problem has persisted, as a matter of fact as i was driving home, upon acceleration it popped(intake) and coughed and sputtered, as if to be fuel starved before it may caught for a few seconds...

FAD2BLK93

Most of these codes look like they are from blowing the fuse...and your gauges. what is your fuel pressure? when you transplanted the enging did you recalibrate the trans for maybe a different gear? did you upgrade the fuel pump when you transplanted?

autobahn_clem

I did NOT recalibrate for the different rear-end. I did use the original fuel pump from the Roadmaster, i have NOT checked pressure.
Let me ask, you don't think it has anything to do with the new Cap & Rotor?

roadhog_113

i am with fad2blck check fuel pressure. Super easy to do. i don't think cap and rotor has anything to do with it at all. check your wiring and fuel pressure. It won't be coil or icm by the sounds of the symtoms. thats just my 2 cents

autobahn_clem

Great, i'll take your word on it. BTW, what should the pressure be, 40-50 psi? Thanks all!

dhdenney

iTrader: (53)

Should be about 43.5 psi with the vacuum line off.

autobahn_clem

Okay, here comes a dumb question... is it best to check the pressure at the valve by the EGR at the rear of the motor? Thanks again.

dhdenney

iTrader: (53)

Yeah the schrader valve is on the crossover between the rails. It's closer to the pass side though.

autobahn_clem

I have not yet been able to pressure test this; however, i have been thinking... let's see what you guys think. My idea is: I have noticed that fuel injected vehicles (or GM vehicles at least) the fuel tank seems to have a small section where the fuel pump sits, this is almost a reservoir in itself as to prevent the sump from taking in air as the fuel sloshes around in the tank itself... My tank, designed for a mechanical no high pressure external fuel pump does NOT have this small section... do any of you think this might be part of the issue as well? Thanks! you guys are great!

autobahn_clem

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Hey guy's, thanks for all the support all of you offer, I certainly appreciate it. This is a continuation of my last post... at this point i have changed the PTS sensor, and finally purchased a fuel pressure gauge that reads about 38psi as a norm, however, the pressure will pulse to about 42psi (and i do mean pulse) when i raise the idle to about 1500 rpm (what i mean as pulse, is that it will go to 42 for about a half-second then back down to 38). Now when i turn the ignition to the run position it will go to about 42 for a second then down to 38psi. Now, at rest with the ignition off, the pressure sits at maybe 10 or less psi... should the line have pressure all the time, because when i installed or removed my gauge there was no fuel escape from the valve as if it didn't have pressure in the line... anyway, thanks again!