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| Username | Post: 88 K3500 7.4L no knock sensor, no ESC Module | |
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LaMort Forum Newbie Posts 8 |
02-14-12 11:40 PM - Post#2190813
Here's the story. I bought this truck cheap...$500, the previous owner had destroyed the motor by continuing to drive it down the freeway when one of the oil cooler lines burst. I had the motor rebuilt, replacing most of the external components (temp and oil pressure sensors, fan clutch, radiator (because of the bearing bits in the oil), water pump, oil cooler lines, etc.), fired it up and let it run for a half-hour, changed the oil and fired it back up again. It was idling pretty high (1200 RPMs) and it never kicked back down. I didn't even think there was a big issue until I took it to get smogged. The techs left it running for 30 minutes in their shop thinking I hadn't let it warm up enough (I wasn't paying attention..that'll learn me) where it sat and overheated (melting the little do-dads that let my engine builder know it's been overheated, voiding my warranty) but they neglected to tell me this happened until later. So I was....rather upset at this point, and I took it to the dealer. They said the knock sensor was "Sending a Flag" and was causing the ECM to retard the timing causing the high temp. Charge $150. I took it home and I looked and looked but could not find the knock sensor. I checked my book and found where it should be...the hole is plugged and no connector/wire. I saw on the diagram it should be connected to an ESC module...I have no ESC module or connectors/wires/mounting bracket for such a thing. I found the diagram online for the 1227747 ECM module and dug the module out of the glove box to find that I have no wire connected to the terminal where it should be (B7). I split the harness open to see if the wire was there but had the ends cut off....nope. I took the truck back to the dealer where I informed the service manager that he gave me faulty information because the vehicle does not have a knock sensor. He replied that every fuel injected vehicle ever produced has a knock sensor. I asked him to show me where it was on my truck....20 minutes later and 3 GM technicians could not show me where I had a knock sensor. He said that even though they couldn't find it, it was there because it was sending flags. Won't be going back there again. Hopefully somebody is still with me here. Is it possible to buy a "Knock sensor kit" (comes with ESC module, knock sensor, and wiring harness) and add it to a no-knock-sensor-having vehicle? http://www.partsgeek.com/catalog/1988/chevrole t/k3... It looks like one end of that cable plugs into the ESC and it has the connector for the knock sensor itself, does anybody know what the other end connects to? I see no matching connector on my engine harness, and since there is no wire connected to B7 on my ECM would it do me any good anyway? The electrical diagram in the Haynes manual shows the knock sensor connecting directly to the ECM, could I just stick one in and wire it directly without the ESC module? Thanks, Scott edit: It didn't pass smog...way too much VOCs at idle. Also I have no trouble codes, and the light is functional. |
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baswm Member Posts 76 |
02-19-12 07:11 AM - Post#2192378
Maybe yours did not come with a knock sensor. http://coloradok5.com/forums/showthread.php?t=2788... Mentioned some 87 -88 did not have them. Sorry I have nothing that will help you. Good luck with it.
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LaMort Forum Newbie Posts 8 |
02-19-12 08:54 AM - Post#2192425
Thanks for that. Based on that post, and doing a little research (what little info I could find anyway), the truck I am working on should have the 1228747 ECM, right? Basically the 1227747 but with no knock sensor......perfect. |
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355Cheyenne Senior Member Posts 3743 
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02-19-12 09:29 PM - Post#2192729
I had an 88 I just sold. 7747 ECU is correct. It should have a separate module for that under the hood. Your truck should have this and the fact it over heated indicated that it should. Step one is to look on the passenger side of the motor. Forward of the starter at the base of the block just by the motor mount is where the knock sensor belongs. In the old days this was a block drain so either the sensor is there but not plugged in or a drain plug is going to be there. Let us know what you find. Also locate the sensor wire which comes off the same harness your starter wires come from. Travel down the bell housing... Next is the ESC module. It is on the passenger side between valve cover and intake some what midway. If it is not there then there should be a wire harness connection. Lets get factory working again and not play with questionable aftermarket quick fixes.
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LaMort Forum Newbie Posts 8 |
02-19-12 09:51 PM - Post#2192743
Thanks for the response but I went over all of those with my original post. The hole is plugged, there is no wire in the harness for the ESC or knock sensor (I even cut open the harness to see if the ends were cut off.), and there is no ESC module bracket or wire connected to terminal B7 on the ECM for the ESC. Even the intake bolts are bolts, and not studs in the ESC location for mounting a bracket like the 4 other brackets on the intake and they match the other intake bolts (same paint and flange size/markings.) I believe it just wasn't there on this truck. I looked at the forum link recommended above and have done some more browsing, and believe there was some reason for some vehicles to have this omitted. I just want to find out why, now, and how to make mine run properly. I'm thinking this 1228747 ECM may be the key. |
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355Cheyenne Senior Member Posts 3743
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02-19-12 10:06 PM - Post#2192747
the 1228747 is not key because that is the most common ECU to find out there. Not only just our trucks but just about everything GM sold in that time. They started the 1228747 in trucks in 87 with the previous body style. My old friends dad had a suburban with a 350 tbi. I remember t/sing a high idle with him years ago and remember checking the knock sensor so I know that it was available from the start. The other thing to consider is that the opinion given to you by the dealer is that the truck over heated because the ecu did not see a knock sensor and retarded timing. Well I have done some programming before on my old 88 and I know there are of course spark tables and an accommodation for the knock sensor in the code, even on the 1228747 with external ESC module. I believe the ESC module is a (forgetting the word) but like an amp that listens to the knock sensor like a microphone and then produces a digital signal indicating knock which is passed to the ECU as a knock count. There is a test sequence to verify the ESC circuit is functional by which the ECU induces a condition conducive to knock and if is sees none then assumes fault. so what we are saying is that your ECU sees fault and is retarding the timing in caution. So if there was a none ESC module I would fully expect this code to not be in the programming so that it is a none issue. So either some one went to great lengths to cut this out and hide it or some one changed the ECU with the wrong prom (programming) Other considerations is the base timing as listed under the hood. Factory is zero degrees at idle with timing wire disconnected. I would still expect to see this even w/ out the ESC circuit as the programming would adjust for this. Either way this is the first I have ever heard of this and the best thing I could come up with to support your theory is Mexico. This truck came from another country that did not require is and some penny pincher did his job a little to well? Also when you key on, engine off, does your SES light come on? I would try pulling codes because this condition should throw a code. Easy to check with a paper click, short Pin A and B I believe, please confirm in FAQ.
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LaMort Forum Newbie Posts 8 |
02-19-12 10:25 PM - Post#2192755
Thanks again. If this ECM was replaced, that means there was an ECM factory programmed to operate without a sensor. Is there a list of the factory proms somewhere that would indicate what programming it has (I.e. AWAK is this setup while ASHE is that setup). This guy took very good care of his truck (it was a hose failure and lack of attention to the SES that blew the motor.), I'd be surprised if he did anything like remove the ESC and knock sensor. He was the original owner, and the truck only has 80k miles. Replacing the ECM is one thing, completely cutting out a set of equipment instrumental to the engine running properly is something entirely different. I am getting/have gotten no codes since the engine was replaced. |
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stumppuller "3rd Year" Gold Supporting Member Posts 437 |
02-20-12 12:11 AM - Post#2192785
Have you verified that you have a 1227747 ECM? If you provide the PROM code I can use TunerCat to get some details as to what applications the PROM was used for. Also, make sure the PROM number on the ECM sticker is the same as the one on the actual chip.
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LaMort Forum Newbie Posts 8 |
02-20-12 08:11 PM - Post#2193162
I've got the ECM in my dingy little fingers. It is indeed the 1227747. The sticker on the case as well as the prom are AFTF. I didn't notice before but it has 95 hand written in pencil on the sticker. Maybe what it was pulled from.....I really do appreciate the help. Scott edit: Does Tunercat give you a list of available PROMs? It would be great if I could know what one I needed to run without ESC/knock sensor. |
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355Cheyenne Senior Member Posts 3743
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02-20-12 08:17 PM - Post#2193166
quick correction to my first post, I copied your 8747 when really I ment 7747. Anyway, if that really is a 95, I thought they changed the ecu coding at some point, there is a big difference from an 88 to a 95 ecu. Can you get a picture? Or better yet, if you pop open the EPROM door easy way to tell that it is a 95. In 95 they had the prom in what was called a calpak. The module contained the CAL module and the PROM in one long blue plastic cartridge. If it was one from 88 to 93~94 it should have two surface mounted chips, one smaller and one much bigger. If you have the ecu where in the access door it has the large blue plastic module that can be removed then indeed it is a 95 ecu and no wonder it isn't running right. Tom
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LaMort Forum Newbie Posts 8 |
02-20-12 08:44 PM - Post#2193183
It has 2 separate chips, no blue cartridge. Must be within the correct year range. I just thought I'd throw that out there, I thought it was odd. There is an eBay seller who is selling 7747s with Moates adapters and can do custom chips. Could I just order one with the KS/ESC turned off? I have to admit I know nothing of custom tuning and next to nothing about spark curves and where the limits should be if errors aren't being dealt with by a safety mechanism (the knock sensor). If I knew the factory limits I would just go for it. I'm way past time vs. money value now. |
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LaMort Forum Newbie Posts 8 |
02-20-12 09:25 PM - Post#2193200
Phone browser wouldn't let me edit my last post..... Just looked at the vin decoder. Truck was built in Ontario Canada eh. Maybe there is a metric PROM available? Ha! Just more info for those in the know. Scott |
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stumppuller "3rd Year" Gold Supporting Member Posts 437 |
02-20-12 10:14 PM - Post#2193211
Does Tunercat give you a list of available PROMs? It would be great if I could know what one I needed to run without ESC/knock sensor. TunerCat doesn't give that detailed of information. Thier CalData does provide some info though... AFTF -1987 Model Year -For ECM 01227747 -Platforms: R20,R2500,R30,R3500,V20,V 2500,V30,V3500 (2wd and 4wd 3/4 and 1 Tons) -Engine: L19 7.4L Gas 8Cyl TBI V8 -Transmission: M20 4 Spd Muncie -Axle: GT5(4.10), HC4(4.56) -Emissions: NM8 (Leaded Fuel) AFTF was superceded three times in 89, AKUL ATPZ AZFW I don't have any of those PROM files on my computer. I'll see if I can find one online somewhere, might help with some more insight...
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stumppuller "3rd Year" Gold Supporting Member Posts 437 |
02-20-12 11:51 PM - Post#2193230
Did some searching for the PROM Bin, but no luck. I re-read your original post, and it seems there was no issues with the motor prior to the rebuild (besides running it without oil). I think the dealer is full of BS about the knock sensor flag, the ECM would be giving you a SES light if it was programmed to use one and it wasn't there. Another item I noticed is that there are 2 different water pumps listed for your truck, a standard and reverse rotation. These are not interchangable. Something worth checking maybe? The high idle is a concern. The computer should have set a code and turned on the SES light if it couldn't get it down to the target RPM once warm and at idle. Is the TPS on that throttle body adjustable and is your coolant temp sensor working? Vacuum leak? Ignition timing set ok? Also, I'm not too familiar with what VOC's are as far as emission testing goes. Around here, they test for HC (hydrocarbons), CO (carbon monoxide) and NOx (nitrogen oxide). Can you post the readings your truck had?
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355Cheyenne Senior Member Posts 3743
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02-21-12 06:40 AM - Post#2193288
I think step one he needs to key on, engine off and make sure that SES light comes on. I am not going to help anymore until I know the status of that light.
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stumppuller "3rd Year" Gold Supporting Member Posts 437 |
02-21-12 10:00 AM - Post#2193352
edit: It didn't pass smog...way too much VOCs at idle. Also I have no trouble codes, and the light is functional. He indicated it's working at the end of the initial post.
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355Cheyenne Senior Member Posts 3743
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02-21-12 10:31 AM - Post#2193362
Missed that, then no doubt this should have thrown a code if what the dealer says is true which means ses light which never came on. Something else is likely going on. I would start by checking base timing and replace thermostat.
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LaMort Forum Newbie Posts 8 |
02-21-12 06:59 PM - Post#2193588
Good points guys. If the pump is incorrect rotation it could be sucking water away from the ecm temp sensor, keeping the ecm thinking the motor hasn't warmed up properly, right? I will run the old hot water test on the sensor itself and meter it to see if it is within range. Base timing with the timing wire disconnected is 4 degrees btdc per the emissions sticker under the hood. I have verified the SES light and no codes. My TPS is not adjustable....I think somebody asked that. I metered it and it had the correct voltage when closed, key on (I believe it was 4.7 volts, but whatever it was was within range) Unfortunately I am on call this week, so I may not be able to wrench again until next Monday, depending on how busy I am....tonight is very busy so far, I haven't been home yet. I will at least get the sensor pulled and dig up the receipt for the pump. The fan spins counter-clockwise when viewed from in front of the truck looking back through the radiator toward the motor. That should be a ccw pump, correct? I have to say again that I really do appreciate the assistance. Edit: sorry, I meant HCs were very high at idle....just painted a Bug and had VOCs on the brain. |
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stumppuller "3rd Year" Gold Supporting Member Posts 437 |
02-21-12 10:56 PM - Post#2193663
To determine water pump go here, www.edelbrock.com/zmags/automotive.shtml Pages 188 (rotation) and 190 (BBC pump years).
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N8sToolz Very Senior Member Posts 2314 
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02-22-12 08:25 PM - Post#2194054
In the 80's Only the 305 and 4.3 had the ESC system. It is possible that is the case even with the newer trucks. Also, if the knock sensor was disconnected and a fault was detected, it would revert to a 'safe' timing curve, or fixed timing. I doubt thats what caused the overheating. The water pump type used is dependent on if its turned by a v-belt or serpentine belt. serpentine belt would spin opposite the engine rotation while a v-belt would spin the same direction.
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