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| Username | Post: 89 5.7 tbi running rich | |
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J-dawg 46 Newbie Posts 7 |
12-14-22 11:32 AM - Post#2851251
I am building a 46 chevy truck on an S10 frame with a 1989 chevy 5.7 tbi engine with the GM#1227747 ECM. The engine seems to be running rich as the plugs are black and the exhaust is black, it idles for a bit and the idle drops and sometimes comes back, but usually stalls. When driving, it backfires out of the exhaust and doesn’t accelerate properly. If I unplug the MAP sensor it idles nice and revs up nicely. No codes are showing up. Fuel pressure is a steady 11-12 psi. Vacuum is steady at about 17-18 inches (elevation is about 2700 feet). Compression is 150-170 on all cylinders. I have removed and blocked the egr from the engine so I am not using the egr wire in the harness. I have replaced the cts, 02 sensor, MAP sensor, IAC valve, spark plugs and wires, distributor cap and rotor and pickup module. Then we tried swapping the computer, coil, distributor, and throttle body from a good running vehicle and it still didn’t help. I have the ground wires to the engine block from the harness, the body to the frame, engine to the frame. Any help would be greatly appreciated. |
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CowboyTrukr "11th Year" Silver Supporting Member Posts 4850 
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12-14-22 12:41 PM - Post#2851255
I know you’ve checked the fuel pressure, but what is your injector spray pattern like? Beautiful fine mist cone? Or, sort of a cone with larger drops/dribbling fuel?
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Shepherd Valued Contributor Posts 2848 |
12-14-22 02:20 PM - Post#2851261
Have you check the vacuum at the map sensor hose? Also when scanning look at what the pcm sees for barometric pressure. Hmm, 89 obd1 may not have that function. |
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CowboyTrukr "11th Year" Silver Supporting Member Posts 4850
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12-14-22 04:43 PM - Post#2851265
You’re right, it does not have that feature.
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J-dawg 46 Newbie Posts 7 |
12-15-22 08:23 AM - Post#2851282
Fuel spray does make a nice cone although it looks a little heavier than the other engine that runs nice. I had replaced one of the injectors because it had a little leak around the top of it. Vacuum at the MAP sensor is good, also tried running MAP from another vacuum port, no change. |
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Tony1963 Frequent Contributor Posts 2070 |
12-15-22 12:53 PM - Post#2851293
The computer expects a certain EGR flow to be mixed in with the intake mixture. By eliminating the EGR entirely, the fuel map is delivering fuel based upon an expected volume. At driving speeds EGR can account for a larger percentage of the total volume so that will have some impact on the mixture. You must have a bank of trouble codes in the computer and that's where you start.
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J-dawg 46 Newbie Posts 7 |
12-15-22 01:43 PM - Post#2851297
I don't get any codes but if I unplug a sensor I get a code so I know it works. It is an aftermarket harness that is a stand alone harness for the engine. My understanding is that the egr doesn't open when the engine is cold or idling and my engine won't idle very long before it acts up. |
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Shepherd Valued Contributor Posts 2848 |
12-15-22 02:45 PM - Post#2851300
If you suspect the egr is the source of your issue, disconnect it. Also look at the coolant temp the ecu sees when warming up. |
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J-dawg 46 Newbie Posts 7 |
12-15-22 03:34 PM - Post#2851306
My egr is removed and blocked off. The coolant temp sensor was replaced and I tested it in water with a thermometer and ohm meter all the way to boiling and is was quite close to the posted information. |
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Shepherd Valued Contributor Posts 2848 |
12-15-22 04:52 PM - Post#2851310
Have you been able to run a live info scan, looking at inputs from all the sensors? Things can be out of programmed parameters that will not set a code in obd1. |
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Tony1963 Frequent Contributor Posts 2070 |
12-15-22 05:00 PM - Post#2851313
This is where you need an old Snap On MT2500 scanner that can read live data from that system and give you an open eye to the system while the engine is running. Why is the EGR blocked off?
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J-dawg 46 Newbie Posts 7 |
12-15-22 10:16 PM - Post#2851320
I don't have a scanner but I might have to find one. When I removed the engine from the donor truck, I removed the air pump, exhaust manifolds, AC and the egr. I wanted to clean up the engine for my new build. |
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J-dawg 46 Newbie Posts 7 |
12-15-22 10:17 PM - Post#2851321
I don't have a scanner but I might have to find one. When I removed the engine from the donor truck, I removed the air pump, exhaust manifolds and the egr. I wanted to clean up the engine for my new build. |
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Tony1963 Frequent Contributor Posts 2070 |
12-16-22 03:26 AM - Post#2851327
In my experience, unless you have someone who can reprogram your PCM, you are always going to have problems. No AIR pump means that you are not pushing atmosphere into the exhaust during warmup and the computer is expecting a rush of fresh air. Again, you will need a scan tool and I have one. However, it is probably full of trouble codes and the computer is doing what it can do based upon the information that it has.
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355Cheyenne Senior Member Posts 3793 
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01-19-23 01:18 PM - Post#2853548
This sounds like a bad Coolant Temp Sensor. Get a ohm meter and ohm it out. if it doesn't match these values below, replace. Coolant Temperature Sensor (CTS): Coolant sensor approximate resistance specifications: 177 ohms @ 212 deg. F. or 100 deg. C. 241 ohms @ 194 deg. F. or 90 deg. C. 332 ohms @ 176 deg. F. or 80 deg. C. 467 ohms @ 158 deg. F. or 70 deg. C. 667 ohms @ 140 deg. F. or 60 deg. C. 973 ohms @ 122 deg. F. or 50 deg. C. 1188 ohms @ 113 deg. F. or45 deg. C. 1459 ohms @ 104 deg. F. or 40 deg. C. 1802 ohms @ 95 deg. F. or 35 deg. C. 2238 ohms @ 86 deg. F. or 30 deg. C. 2796 ohms @ 77 deg. F. or 25 deg. C. 3520 ohms @ 68 deg. F. or 20 deg. C. 4450 ohms @ 59 deg. F. or 15 deg. C. 5670 ohms @ 50 deg. F. or 10 deg. C. 7280 ohms @ 41 deg. F. or 5 deg. C. 9420 ohms @ 32 deg. F. or 0 deg. C. 12300 ohms @ 23 deg. F. or -5 deg. C. 16180 ohms @ 14 deg. F. or -10 deg. C. 21450 ohms @ 5 deg. F. or -15 deg. C. 28680 ohms @ -4 deg. F. or -20 deg. C. 52700 ohms @ -22 deg. F. or -30 deg. C. 100700 ohms @ -40 deg. F. or - 40 deg. C.
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jbknight311 "5th Year" Silver Supporting Member Posts 1077 
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02-13-23 10:44 PM - Post#2854462
I will agree with programing the ECM for the engine as it sits. You have done mods, even if only deleting things, that the ECM thinks are there. There are a number of custom tuners that can send you a flashed chip for your setup. That can be your starting point and he will make changes based on what is happening or what you want. You could possibly have a bad connector or plug on your new harness or old reused sensor plug. A wire under the intake in back of the engine will be fun to find (yep, got that tee shirt. You can't really start from engine with parts removed. Yes that makes it a pain. Now you have to find out how each deleted item worked and when, under what conditions and go from there. Doubt you will get elp from a shop as they can't mess with emissions.
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Bill K.b Senior Member Posts 4529 |
02-17-23 03:57 PM - Post#2854639
1989 TBI setups used a speed sensor located on the back of the instrument cluster. I am guessing you don't have one. There was one you could buy to add from the people doing jaguar 350 conversions, jagsthatrun was the website. Without that sensor the ECU doesn't know how fast you're going and runs the engine rich.
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