HELP PLEASE! EFI Making my head hurt. I may go back to Carb - Team Camaro Tech
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post #1 of 13 (permalink) Old Feb 20th, 11, 03:57 PM Thread Starter
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HELP PLEASE! EFI Making my head hurt. I may go back to Carb

I really need some help. My Truck started acting up, surging and dieing. It s a 1989 GMC 5.7 TBI engine. Bone Stock. I could not find anything causing the problem. I replaced Plugs, Wires, Cap, Rotor, IAC, TPS, The whole shotgun thing. I was told by a Local Wrench that the shaft's in the throttle bodies wear causing this problem, so I was dumb enough to let him replace it. No Change. If anything it is worse! It only has 90,000 miles on it. I changed my oil every 3,000. The compression is good. The exhaust does not seem to be plugged. I have gone from thinking about Fuel Injection on my Camaro to the point where there is No way in heck I would do that. If I can not get this figued out soon, It is carb time for the truck. I can fix a carb. This computer crap is going to give me a stroke. Does anyone have an Idea what this is all about?

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post #2 of 13 (permalink) Old Feb 20th, 11, 04:03 PM Thread Starter
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Re: HELP PLEASE! EFI Making my head hurt. I may go back to Carb

One additional thing, There is no way to check fuel pressure on this setup, but the pump cycles, and you can feather the rpm's up till the engine is at high RPM's, and it goes like a house on fire. It just will not idle. It surges up and down for a few minuets then just dies. It is not drivable now. If I had some black powder I would blow it up!

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post #3 of 13 (permalink) Old Feb 20th, 11, 04:16 PM
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Re: HELP PLEASE! EFI Making my head hurt. I may go back to Carb

Sounds like a intake vacuum leak... Have you tried Google and typed in your info just to see what pops up?

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post #4 of 13 (permalink) Old Feb 20th, 11, 04:20 PM
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Re: HELP PLEASE! EFI Making my head hurt. I may go back to Carb

Any engine codes? Is your check engine light on?

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post #5 of 13 (permalink) Old Feb 20th, 11, 04:53 PM
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Re: HELP PLEASE! EFI Making my head hurt. I may go back to Carb

After finding the codes and deciphering them, these DTC's will get you in the general area.
As suggested, more than likely a vacuum leak. Put a vacuum gauge on the manifold or TBI nipple and it should indicate a steady 20" of vacuum.
EGR valves are famous for leaking. Only way to check is to pull it off, turn it upside down, and pour gas into one port. If leaking, gas will show up in the other port.
Another common leakage point, and would have been found during the TBI swapout, is the TBI-to-intake gasket. It leaks across the rear due to poor clamping.

Have you done a base timing and set base idle? Follow instructions on the hood sticker.
After setting base idle, you'll have to reset TPS voltage to avoid a DTC.

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post #6 of 13 (permalink) Old Feb 20th, 11, 06:43 PM
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Re: HELP PLEASE! EFI Making my head hurt. I may go back to Carb

Those vehicles had a common problem of the vacuum line coming off the MAP sensor. It is (black square box appox 1.5" x 3"x 3/4") located behind the air cleaner on the pass side. When the line comes off, it goes full rich & will surge, sputter etc. Hopefully this is your problem as it is an easy fix.
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post #7 of 13 (permalink) Old Feb 20th, 11, 07:48 PM Thread Starter
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Re: HELP PLEASE! EFI Making my head hurt. I may go back to Carb

No Check Engine light. I checked all of the lines at first. I was thinking the Power Brake booster may be the problem, and I pulled the line and plugged it. The Map Sensor and th EGR control are on a metal bracket above the passanger side valve cover. The lines to to both are fine. I cannot find my vacuum gauge, but I I'll drop by Harbour freight and get another in the morning. I am also going to get a couple of cans of Carb Cleaner to spray around the connections to see if there is any reaction. This is usually a good way to check. There are not alot of places for there to be leaks. That is why I have been pulling my hair out. If it were something simple I should have caught it. Of course it will be and I will be really embarrased.
Is it possible that the Distributor is bad? Could that cause this kind of problem. The other guy thought the Throttle body shaft was allowing a vacuum leak, and that is why I replaced the Throttle body. I have seen Fords suck in the back of the intake manifold gasket, but usually not an engine this old.

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post #8 of 13 (permalink) Old Feb 20th, 11, 09:52 PM Thread Starter
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Re: HELP PLEASE! EFI Making my head hurt. I may go back to Carb

OK,
I sprayed Carb cleaner all around the base, the Manifold, at the shaft pivots, and on every vacuum line. No Change. I sprayed it slowly down the throttle body and it smoothed right out. I took some Remoil, and as I would spray it in the Throttle body it would smooth out for a few moments, till it had all evaporated, and the idle would slowly come down, start to surge ad then it would die. I am telling you, That Carb is looking better every day. I pulled the filter to see if there was anything to restrict the flow, Nothing. You can clearly see a good fuel spray from each injector. I am going to work on it again after work on Monday, and then list it on Ebay. I am so over fooling with this. If anyone has any suggestions, Please let me know.
This happens hot and cold, so I do not think it is anything to do with the O2 sensors.

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post #9 of 13 (permalink) Old Feb 21st, 11, 03:20 AM
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Re: HELP PLEASE! EFI Making my head hurt. I may go back to Carb

If it happens during cold & hot, could be the two-wire coolant sensor, should read 5K ohms or more when cold, 200 ohms when operating temp, or the connector plugging onto it.
If you think it may be the O2 sensor(s), unplug them, ECM will default to a steady input of reading a good sensor signal.
There is a Schrader valve to measure fuel pressure, 9-13 PSI.

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post #10 of 13 (permalink) Old Feb 21st, 11, 05:12 PM Thread Starter
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Re: HELP PLEASE! EFI Making my head hurt. I may go back to Carb

Ok, This is what I found. I unplugged the MAP sensor and plugged the line to prevent a vacuum leak. Then Hit the key, and it fired right up. The idle is perfect. Went to Autozone and picked up a new MAP and problem solved. The map I had was already a new one, it was not working correctly..
Thank you Lonnie P for the idea. It was your idea that sparked the thought.

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post #11 of 13 (permalink) Old Feb 21st, 11, 06:30 PM
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Re: HELP PLEASE! EFI Making my head hurt. I may go back to Carb

Glad I could contribute.

The TBI's are rather crude & rely a lot on the MAP sensor to operate properly.
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post #12 of 13 (permalink) Old Feb 21st, 11, 06:58 PM
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Re: HELP PLEASE! EFI Making my head hurt. I may go back to Carb

F'ing aftermarket parts. Nothing works like AC Delco. Had an idle problem in my S10 and first thing I did was replace the IAC valve after cleaning the old one seemed to help. Didn't fix it so I wound up replacing practically everything else and it was no better. The problem? The new off-brand IAC valve was bad. Oh well....got spares for everything else now I guess.

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post #13 of 13 (permalink) Old Feb 24th, 11, 07:25 PM Thread Starter
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Re: HELP PLEASE! EFI Making my head hurt. I may go back to Carb

I went ahead and used a can of Sea Foam and ran it through the Vacuum line. That actually helped the way the truck ran also. It runs pretty good now. It still will stall from time to time when I pull up to a stop, or stop when backing up. I did go ahead and list the truck on Ebay to sell. If someone wants a good 350 engine. It is really good. The truck itself is a tank. It is a 1990 Long Bed 1500 with a tall camper shell. I feel like I am back driving my Freightlinner when going down the road.





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Balanced 350, Eagle rotating assy, Mahle Flat top Forged pistons, AFR 195 cylinder heads, AFR Hydrorev kit, Comp Cams Hydraulic Roller Cam, comp Pro Mag Ultra Roller Rockers, Edelbrock AirGap RPM Manifold.
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