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73-87 Chevy _ GMC Trucks => Suburbans => Topic started by: 90_suburban on October 05, 2018, 01:01:41 PM
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Ok I have a 90 r1500 5.7 tbi 190,000 miles. I stopped and got gas roughly 18 gallons to top off the 40 gallon tank. Drove it about 20 miles home and it died pulling into my driveway started right back up and pulled it into the garage with it dying once again, started right back up and finished parking. Couple of hours later went to go pick my kids up from school and it started up no problem and when leaving it sputtered and died. Started right back up and got going down the road it kept hesitating and sputtered some more and died again. This time it wouldn’t start back up without feathering the gas managed to get back home with it and take another vehicle to pick the kids up. My thought was bad gas.
Next day I replaced the fuel filter and dumped some fuel treatment in the tank. Now sometimes I can get it to start other times it won’t start at all. If I managed to get it started and try driving it, it will sputter some but sometimes run fine. I have managed to siphon around 8 gallons out and burned some out driving as well and topped off with premium gas close to 12 gallons. Now my thought is that it is something else and it just happened shortly after filling up and the gas is fine.
I picked up a ADAL scanner from oriellys too dang expensive but bought it anyways. My cel isn’t on but I pulled codes 32,34,42 from it. Being I have another suburban an 88 v2500 I changed the map sensor with no luck and I also swapped the whole tbi unit. This should rule out the map, iac motor, tps, the injectors, and fuel pressure regulator. Still no difference so I swapped the ignition control module one of the connectors on the 90 was broken so I thought it could be bad. Right now it is still the same. I have only owned it about a month and put around 1000 miles on it. Within the last year the PO replaced the fuel pump as well.
Anyone have any thoughts on where to start. I do have a new coil that will be here tomorrow I am going to try out.
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Pull the distributor cap out and check if ti looks good, pull the whole distributor out.
I had one dying whe going in gear and this was the post on it.
http://forum.73-87chevytrucks.com/smforum/index.php?topic=3984.0
BTW a wire between the AB terminal on the ALDL will flash the codes.
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I pulled the cap today when replacing the ignition control module both cap and rotor look relatively new inside. I bought the actual scanner so I can look at the little bit of live data it will show as well. According to it the map seems to be putting out good voltage it does show it to be running lean though when idling it will switch to rich for a second when revving up.
I will take a look at that thread and see what I can tell.
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can you swap computers?
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can you swap computers?
Yeah I could pull the one out and swap it in the other and give it a try. I guess the promm is the same in both of them?
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can you swap computers?
Yeah I could pull the one out and swap it in the other and give it a try. I guess the promm is the same in both of them?
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cant say 100%, the only issue i can think of is the trans and thats because im not sure how the 700r4 works in relation with the ECU if at all. does it seam to run different depending on if the engine is hot or cold?
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Holy parts cannon Batman.
Check your fuel pressure, check for spark, check for injector pulse. Don't keep swapping parts around as you may begin to compound issues before identifying your initial issue.
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Holy parts cannon Batman.
Check your fuel pressure, check for spark, check for injector pulse. Don't keep swapping parts around as you may begin to compound issues before identifying your initial issue.
I definitely have spark and fuel. With it cold this morning I was able to get it to run but wouldn’t hold a steady rpm. Once warmed up I couldn’t get it to start but for 1-2 seconds. I unplugged the idle air control motor and it fired right up and is idling at a high rpm but steady. I’ll test the iac motor and see if it is bad.
Not sure if it has anything to do with it or not but the brake light in the dash came on as well and hasn’t went back off. My thought is from braking with the engine off several times has caused it not sure what sets it.
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After plugging the iac back up while it was running. It seems to be running perfect for now.
(https://uploads.tapatalk-cdn.com/20181006/0c06c3c2719859223a942b0c1a587b6e.jpg)
Screenshot of the live data at the moment. Seems to idle a little higher than before but could be the difference in the tbi units from the 88 to 90.
I turned it off and it started back up running normal still. Guess I’ll see how it goes.
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Didn’t last long back to how it was I’ll get to testing the iac hopefully that’s all it is.
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Seems like the iac is working. Right now it idles around 1000 which is high but it does idle. When I put it in gear it drops to 750 and you can hear the iac open up and I can watch the counts change on the scanner as well until the Rpms get to 850.
When I put back in park or neutral it idles as 1400 way high and the counts on the iac don’t change immediately. It take about a minute then it will slowly decrease back to 1000 rpms idling. It starts and runs fine with a little stumble coming to a stop.
Besides the computer what controls the iac motor? If it is only the computer then my assumption would be that it took a dump?
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Idle just after startup
(https://uploads.tapatalk-cdn.com/20181006/fa010192d5372b26e7347675a625357e.jpg)
In gear
(https://uploads.tapatalk-cdn.com/20181006/fb8139dada41c3c824020a9ccf553250.jpg)
Just after shifting back into park
(https://uploads.tapatalk-cdn.com/20181006/f556f66f3917fa57d3c9562c0eb740d0.jpg)
After shifting into park and the rpms coming back down.
(https://uploads.tapatalk-cdn.com/20181006/88b3140fa21f0094c4a3594e9c3d2927.jpg)
Iac counts start close to 100 just after start up climb to 140 in gear then back to idle the drop and steady out around 55.
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Okay so don't blame the victim. If it's lean, idle is high and IAC is way off the mark, what's it doing? Compensating for a vacuum leak most likely or an extremely lean condition. Remember, garbage in garbage out. Are you chasing the symptom or the problem? So what's the issue now, just high idle? No drivability?
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Okay so don't blame the victim. If it's lean, idle is high and IAC is way off the mark, what's it doing? Compensating for a vacuum leak most likely or an extremely lean condition. Remember, garbage in garbage out. Are you chasing the symptom or the problem? So what's the issue now, just high idle? No drivability?
Most likely I’m chasing the symptom instead of the problem.
Mainly the issue now is high idle and the counts are high on the iac which is completely open. The O2 reading shows lean but if you watch the live data about every 2 seconds it bounces between lean and rich so my thought is that’s working correctly.
Correct me if I’m wrong but if it is a vacuum leak wouldn’t it go closed reducing the air needed?
I have sprayed carb cleaner all over and can’t find a vacuum leak (not that I notice anyways). Now even though the idle is high it will still occasionally not want to start or it will stall out it will also occasionally surge and not have a steady idle. It does still show to have a code 32 map sensor low voltage as well.
I guess it possibly could still be bad gas and I am chasing the symptoms as you say and the problem is actually elsewhere.
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What's the TPS voltage?
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Tps voltage is .61 little higher than the .55 you recommended in the other thread. I was just reading more on that thread.
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I have a thought but don’t know for sure. My thought is that the iac counts are off because the computer is telling it to step and it only moves some of the time.
I was messing with it a little bit ago and after taking it around the block the counts stay full open at 145 (highest I have seen it go). When coming to a stop they come down and then go back up the 145 sometimes dying and sometimes it doesn’t. Idle in gear is 145 counts on the iac and 850 rpms I also watched it stay steady at 850 rpms and the counts go from 95 up to 145. On the way back from around the block it died and wouldn’t start back up until I unplugged the iac it started and then I plugged it back in. Made it home and when I put it in park the rpms climbed to around 1400 and the iac counts went from 145 down to 10 and idles at 1000-1050 rpms.
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Is the ECM throwing codes? If so what are they?
You might try this ( I just skimmed these posts) it will reset the IAC.
Disconnect the battery for about 30 seconds and reconnect.
Jumper the A&B terminals on the ALDL connector
Turn the key on and leave it on for about 30 seconds.
Turn it off and remove the jumper.
Then try to crank.
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Is the ECM throwing codes? If so what are they?
You might try this ( I just skimmed these posts) it will reset the IAC.
Disconnect the battery for about 30 seconds and reconnect.
Jumper the A&B terminals on the ALDL connector
Turn the key on and leave it on for about 30 seconds.
Turn it off and remove the jumper.
Then try to crank.
Only code it is throwing is code 32 low map sensor voltage. I’ve tried 2 different map sensors and both do the same thing.
I have tried the reset on the iac multiple times with no luck. With it fully extending blocking all air flow it will start but only stay running if I am giving it throttle.
I have read through the post on your truck. I have tried almost everything that you did as well. I don’t have a fuel pressure gauge adapter so I have one that will be here tomorrow and I will see what the fuel pressure is actually doing.
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Tee in at the fuel filter. If all checks out as you say then I would suspect low fuel pressure.
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Will get that checked tomorrow when my adapter comes in. Hopefully that is it.
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Ok got my fuel pressure adapter in. Steady 12 psi in gear out of gear stays steady. Also got an iac circuit tester and it shows the circuit to be moving both directions.
I was mistaken on the code still showing. It’s a 34 not 32.
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This may be a stupid question as I know very little about TBI engines. Do TBI engines use a EGR valve?
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This may be a stupid question as I know very little about TBI engines. Do TBI engines use a EGR valve?
Yes they do use one. I haven’t made sure it’s not stuck open yet fixing to check that. I have pulled the vacuum hose off of it and it makes no difference and also pulled the oil cap off with no difference. The oil cap was something I saw in another thread.
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Looks like the egr checks out. With it running I pulled open the egr manually and it idled down and tried to die. Closed it back and it idles again. Still idles at 1000 in P/N 850 in R/DL going back into park 1400 until the iac counts come down.
Every time I try taking it around the block even if it seems to run fine in the driveway. It will die coming to a stop and it won’t always start back up unless I unplug the iac and plug it back in.
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Went back out and messed with it some more. I did notice that it seems to idle at a normal rpm when in open loop (didn’t have the scanner turned on yet so don’t know the actual value). As I was turning on the scanner and opening up the live data it went into closed loop and the idle jumped up.
Does this mean the O2 sensor is telling it to add more air?
Could the O2 sensor be bad and causing the issues with idling?
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Make sure the vacuum supply line to map sensor is not plugged up with carbon. If it is, map sensor will respond to slow and have skewed readings.
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Make sure the vacuum supply line to map sensor is not plugged up with carbon. If it is, map sensor will respond to slow and have skewed readings.
Checked and it’s free. With it disconnected the map voltage goes high and throws code 33.
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is it smoking at all? i saw its reading lean but wondering if the computer is trying to compensate and giving too much fuel. not 100% sure how these tbis work and im still learning
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Code 34 - MAP Sensor
High Vacuum
Low or no output from
sensor with engine
running
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also see this
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It does smoke just a little occasionally but it did that before. Little bit of white I think it’s a little oil burning. Clears up pretty quick though.
Looking at the testing you posted for code 34 it shows it is an intermittent code being my voltage is around 1.5 while idling. I haven’t actually checked the timing I’m pretty sure it hasn’t been adjusted since new being the bypass connector is still taped to the harness can’t unplug it without taking the tape off. The lean showing on the screenshots bounces every 2ish seconds between rich and lean which I assume would be normal ( constantly adjusting).
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should of added this first
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should of added this first
Looking at that it’s possible I set the code from having the throttle over 20% when trying to get it restarted. Possibly. I can reset the codes and see if it comes back and try not giving it any throttle while starting as to not set it from that.
I have to get a new fuel regulator tomorrow for it. I pulled it just for peace of mind that the spring wasn’t broken or diaphragm torn. The diaphragm is too soft to reinstall without the guide pins supplied with a new one.
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Have you checked timing? A loose timing chain possibly?
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Have you checked timing? A loose timing chain possibly?
I haven’t checked yet my timing light only wants to work occasionally so I will be picking another one up tomorrow. Loose chain is possible with 190,000 on the clock. Hopefully it’s not.
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If the timing is jumping all over it would explain a lot of what is going on
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Just checked the time and it’s 0* with the wire disconnected and 24* connected and idling. I did reset the codes and was watching the live data. All of a sudden lost all voltage to the map and it died started back up and can’t get any voltage reading on the map. Swapped the map out with a different used one same thing. I’ll be looking into what is causing no voltage reading.
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Checked the map sensor wiring. If I jumper terminal BtoC I get 5 volts. Check resistance back to the ECM and all check good readings were grey wire 1.1 ohms lt green wire 2.5 ohms and purple wire 1.1 ohms. According to the troubleshooting diagram above the ECM is bad.
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Before condemning the ECM, disassemble and clean all ECM ground connections to the cab and engine. Turn on the windshield wipers and verify there is zero voltage drop between the cab sheet metal and the battery negative post. Similarly, verify the ground connection between the engine and the battery negative post. Disconnect the harness connectors from the ECM and wash the wire terminal ends and PCB edge contacts with CRC QD Electronic Cleaner or equivalent. Using care not to deform the board edge terminals, slightly raise the terminal ramps using a pointed, narrow, curved scribe or similar tool to subtly increase the tension between the harness terminals and the PCB. Remeasure the continuity of the MAP to ECM wires while very gently wiggling the wires to make sure none are severed internally. Then retest. Note that disconnecting the ECM will clear all stored codes and reset the adaptive memory.
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Definitely is a wiring issue. Wiggling the wires for the map I can lose all voltage or get voltage back. I’ll dig into to harness and get that fixed and see where I’m at then.
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Got the wiring issue for the map sorted out. Loose connection on factory crimp for the 5v reference. Now I have 0.1 ohms on all 3 wires. Only issue I still can’t figure out is why it is idling at 1000 with the higher than normal iac counts.
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Check all the connections then. You may find more bad ones
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Went through pretty much all sensors and the wiring checks out. I checks for vacuum leaks again and finally found the intake manifold leaking between cyl 3 and 5.
I also noticed that it will idle fine at 650 in park and 550 in gear until I turn the scanner on? What would cause the idle to go up when the scanner is turned on?
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Looks like as long as I don’t hook the scanner up it runs perfectly fine even with the slight vacuum leak in the manifold. Drove it into town and back around 15-20 miles stop and go traffic and even stopped got some food and it started right back up and drove just like it did when I bought it.
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Maybe a bad ground?
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Might be a bad ground on the cigarette lighter. The scanner gets power from there. Might be causing it to idle high cause it is pulling a ground through the aldl? No telling.
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The cig lighter ground itself on the dash, there's a grounding strip above the ebake pedal. Not sure where the ecm grounds.
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Connecting some scanners (including Bosch) to OBD-I initiates an ECM service mode that affects idle RPM among other parameters. It is normal for the idle RPM to increase because of it.
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Connecting some scanners (including Bosch) to OBD-I initiates an ECM service mode that affects idle RPM among other parameters. It is normal for the idle RPM to increase because of it.
That makes sense. They should put a warning lol then people won’t chase a problem that isn’t all there.
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Figured I would give an update. I’ve driven it around 100 miles maybe a little more. So far so good. I did have one little stumble in the idle but nothing else. Still running really strong.
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