Mismatched 1988 V10 Mismatched Suburban

[1967KaiserM715]

It's normal to drop rpm going into a gear, maybe not that low, but 200rpm difference isn't necessarily a bad thing, you can try upping idle in park to 950, and see what that does

Sent from my Lenovo TAB 2 A10-70F using Tapatalk

[MuddiGGEr25]

I know idle drop is normal, but the PCM is saying im at 1000-1150, but the tach says 850 almost exactly, and when i drop in gear i go as low as 400 or as high as 600ish, usually i dont drop that low unless its a lopey cam.


I dont have an idle adjustment on the TBI, or atleast not that i can access.

[frotosride]

I have and have always had the same issue. Before I changes my IAC and reset the value the truck would die on me every so often when shifting into gear from park or R-D, I didn't have a tach then but after using my cheap one for the last 4 months b4 I put it on the run stand  (which I originally purchased it for) I know my idle in gear is between 550-600 max. But no more stalling!

(1000posts)
Based on your earlier discriptions it sounds like you have a true '87 accessory drive so it's likely you just have a slight reman keeping within factory specs.
I currently have 35's and 3.73's it's ok but I feel like the engine would appreciate a taller gear at times. My shift points are all below 5k I'd say between 46-4800 at best. This is with all OEM running gear minus a few small engine bolt ons.

[frotosride]

The PCM'S rpm readings intrigue me because when I shift into reverse or drive it often feels like I'm shifting from that rpm but according to the tach it's more like 900-1k then a drop to around 550-600

[frotosride]

There is an idle adjustment but it is capped off for a resone. If you have reset your IAC and have no stalling issues then I wouldn't bother with it but if you are intrest ed in the name of science... it is behind the plug on the driver's side just inboard of the throttle blade shaft. Drill a hole and get a #15 or #20 torques bit and pay attention to how much you turn it. I really wouldn't recommend adjusting it unless you are trying to test what the ECM is seeing.

[MuddiGGEr25]

I have and have always had the same issue. Before I changes my IAC and reset the value the truck would die on me every so often when shifting into gear from park or R-D, I didn't have a tach then but after using my cheap one for the last 4 months b4 I put it on the run stand  (which I originally purchased it for) I know my idle in gear is between 550-600 max. But no more stalling!
Based on your earlier discriptions it sounds like you have a true '87 accessory drive so it's likely you just have a slight reman keeping within factory specs.
I currently have 35's and 3.73's it's ok but I feel like the engine would appreciate a taller gear at times. My shift points are all below 5k I'd say between 46-4800 at best. This is with all OEM running gear minus a few small engine bolt ons.

I have changed my IAC with a known good one off a 1ton van with no NO idle or running issues


I havent had the pleasure of stalling lol. is yours a 87 350 also? I havent been able to find the forum posts again, but i read on 2 different ones, where a few people said redline on the 87 block OEM was like 4800. then increased after some design changes that year.

I am now running 4.10 8 lug axles with oem tire height for now, i have noticed a small increase in mpg over the old 3.42 6 lug. but my effective ratio will be 3.71 if I buy the 35's.

Even towing 10,000K+ with the 5.7L it was not lacking the low band at all, I could get through each gear relatively quickly. mind you i am comparing to a mid 90's K2500 with the 6.2L turbo, a early 90's Chevy 3500 minidump truck with 6.2L turbo, and a 2000's 2500HD with the larger gas engine (i dont recall it right now)

I can pull an equal or identical load just as well as the diesels and better than the gas, (but the gasser had sensor issues), I am talking everyday pulling, 2,000-4,500lbs of lawn and snow equipment for 8-16 hours per day.

I am just barely slower (about 8-10ft) than a mid 90's tahoe with a slightly modded 5.7L vortec, 3.73 AR, about 1,500lbs lighter, and steeper 1st gear. that was with the 3.42 vs her 3.73 AND higher 1st gear. now with the 4.10, im pretty sure i could creep past.


I would like to verify stock OEM 87 engine specs but i am having no luck locating any info specific to the 87 block and its specs, or the pulley arrangement for the A/C


And no im not worried about the adjustment,and now that you described it i think i have read about it before, but my memory only lasts about 1-2 weeks, otherwise i cant remember without a trigger.

If you go up to my youtube links, i have many videos of the PCM readouts

[MuddiGGEr25]

what i did find on gmtuner.com was this
                      body                                    CR        HP                     TQ
1987   V8-350   F   8   Tuned Port FI   9.0   225 @ 4400   300 @ 2800
1987   V8-350   Y   8   Tuned Port FI   9.5   240 @ 4000   345 @ 3200


1987-up 350's had hydraulic roller lifters, new design centerbolt cylinder heads, and one-piece rear main seal cranks.



and this on full size chevy:

I have a 1986, 350 from a 3/4 ton in my 74. These engines from the early mid 80's 3/4 ton and 1-ton have a real truck cam in them. Shift at 4800-5200. It loses power at higher rpms and is very noticable at 5200 and above. However the engine should rev to 5500-5600 safely if its in good shape.

So i really really dont know what to believe and no papers on the engine, dont even know what shop did it, but according to the gm tuners page, my TQ "Stock" should stop 2800 or 3200 RPM, but i know mine isnt done till 3700ish, hardly any slippage at the TC either, its really tight



PS I meant 6.5L turbo NOT 6.2L sorry i drove about 8 hours today on maybe 5 hours sleep, and loaded and unloaded 2 axles and 6 tires, and tools bymyself, from the ground to my tailgate like 3ft up with no leverage -.- so i am like out of it right now lol


just googled the specs on the 6.5L we had in 2 of the work trucks for comparison. the 3500 had a 4.56 rear according to the glovebox, and im 99% the k2500 had 4.10 when i had the papers around in the shop. so similar weight "empty" similar ratios, and similar tires, the 3500 had the nv4500, and the k2500 had 4spd auto.

Engine Weight:
Roughly 750 lbs
Max Engine Speed:
3,400 rpm
Peak Horsepower:
Introduced at 180 hp @ 3,400 rpm. Offered as high as 215 hp @ 3,200 rpm.
Peak Torque:
Introduced at 360 lb-ft @ 1,700 rpm. Offered as high as 440 lb-ft @ 1,800 rpm.


i know im kinda comparing apples to oranges, but at the same time, highway or city, I could do the same load just as easily with my 87' 5.7L TBI as the 5.7L, no my hitch or total weight capacity was not the same, nor do i have the O/D but we "Raced" a couple times with trailers attached because my boss was adamant that his 6.5l was superior, we loaded the exact same equipment onto 2 almost identical trailers, about 4,000lbs behind us each, again approximate, it was a couple 0turn mowers, and concrete. He had me in 1st gear by about an entire length, but then he went 2nd and I was still in first and gaining, then i shifted to 2nd and overtook him. then in 3rd we were neck n neck. we also raced on a dirt road all 3 of us empty, his k2500, the other guy had his 1500
(dodge i think) and mine, we held neck and neck 4x4 for 3 miles at 95mph, none of us could safely go faster on that road, way too many bumps and loose gravel. but nobody won that day. I never let them live it down that a 87/88 suburban kept up with his K2500 diesel and his buddies 2014 1500. nevermind that i weigh alittle more lol. oh and that dirt road race was with the 3.42 GM10 6 lug axles.

[MuddiGGEr25]

Oh, and 3700rpm peak tq on 87 no ethanol gas, i dont run ethanol because i notice a significant power and mpg loss, also I get an extra 1-3mpg running 91 with no ethanol, and noticeably more power under the "pedal" lol but sometimes the per gallon cost isnt worth the higher octane. but since i do get an improvement using the 91, im wondering if my CR isnt increased over stock?

[MuddiGGEr25]

I made a new thread about my most recent discovery since this thread is and isnt on track with what i discovered. and i wanted a clean slate for the diagnosis for future and current members in case they run into the same issue. however I will copy and paste here what I discovered while reviewing my video logs and reading ALOT on programming the PCM, and about the BLM and INT readings, and open/closed loop etc.


:Ok, so i think i figured out my issues after reading hundreds of more pages regarding the Integrator and BLM values, and yada, yada, then I went back to my recorded video of the live data output on the shop snap on scanner. i noticed the 02 only really varies 430-451mv, it is always in open loop even at 208F, the knock counts are ridiculous. my BLM and INT both stay at 128, which from what i have read is caused by the O2 not letting the PCM head into closed loop.  my MAP was saying 8-9in but my manual gauge is reading double that, i cant believe i didnt see that before.I know at some point in the last 2-3 weeks i did find a sizeable vac leak and sealed it, but I dont remember when, and it didnt affect performance so i didnt mention it. Nonetheless, I am gonna try to find my other MAP I had extra around and then record the data readout again on monday after i punch out. But before I start on my data recording on monday:


1. Is it true that it cannot enter closed loop without the O2 sensor reaching a preset temp/mv reading? its not original exhaust and it is very possible that the sensor is cooled off by that point. I will check sunday afternoon to see if it is a lazy O2 or wideband. i thought i saw 3 wires but cant remember.

2. VSS input, the PCM/ECM whatever you want to call it, its got a spot for it, did the 700R4 in 1987 have a VSS for the ECM? and if so will that control the open/closed loop at all? and even if it does not, can I get a VSS module for my TH350 and eventually change out my dash with all digital speedo & gauges?

3. After I get it to enter closed loop, the A/F learned should switch to YES, and my knock counts should be completely or almost gone after it "learns" the block correct?

4. If all above are corrected, then I should get 100% performance back from the PCM after a few drives? assuming my used pump is in fact good.

[frotosride]

I'm not sure exactly how the o2 sensor plays into closed loop but I do know that anything above 160* should be closed loop. Also the location of your o2 sensor will pay a huge part in its MV reading. It should be @ 600* to function properly and if it isn't high enough in the exhaust it will not reach temp and cause a 470 (ish)MV reading.
I would check the o2 temp to justify the MV readings you are seeing
2. There is a VSS sensor in the trucks with 7700r4's but they are mostly located in the dash. Behind the speedo there's an optical sensor that reads a reluctor ring which is attached to the speedo.

3.

[MuddiGGEr25]

I'm not sure exactly how the o2 sensor plays into closed loop but I do know that anything above 160* should be closed loop. Also the location of your o2 sensor will pay a huge part in its MV reading. It should be @ 600* to function properly and if it isn't high enough in the exhaust it will not reach temp and cause a 470 (ish)MV reading.
I would check the o2 temp to justify the MV readings you are seeing
2. There is a VSS sensor in the trucks with 7700r4's but they are mostly located in the dash. Behind the speedo there's an optical sensor that reads a reluctor ring which is attached to the speedo.

3.

I have read on the GMtuners and a couple other knowledgable sources that until the o2 reaches said temp then the computer cannot enter closed loop and i have read many posts of indivuals confirming the same.

I checked the physical o2 sensor and there are no wires in it at all anymore, and the only connector near enough is a 4 plug with 3 wires in it. I thought it might be a "custom" heated o2 connection that was installed during engine swap. but the colors dont make sense for a o2 sensor.

and the wires for the aformentioned connector have melted to the exhaust so i would have to replace them anyway

There is no single wire anywhere nearby that could be the existing o2 wire and this forum:  http://67-72chevytrucks.com/vboard/showthread.php?t=352321


it says i need to find the purple D7 wire for the sensor wire for the 02 on a 1987 harness, and since my block is obviously an 87 it would make sense if they in fact pulled everything from 1 donor.

I was wondering if getting a VSS adaptor for the TH350 if that would help the engine at all.

I also have  code for open/short/faulty o2 but im getting mid 400mv up to mid 500mv readings and i dont understand how that is possible with nothing connected

[frotosride]

O2 temp is definitely a doctor but having it connected to the ECM is the first step...jk!
The VSS signal is paramount for any computer controlled vehicle. The ECM uses it to adjust fuel and spark tables. You will never get it to run right without a VSS signal with the right pulse. Check behind the cluster BC a gage swap would have been easy for them to do and you wouldn't know it was there without taking out the guage panel. But I do believe it's a 4k pulse so an adapter connected to the VSS input is a good idea.
Fix the O2 first of course. I wouldn't imagine a complete swap and them leaving out the VSS wire

[MuddiGGEr25]

Well they went from 6.2l and 700r4 which i thoight i read somewhere that it had electronic speedo and a vss in the trams somewhere amd now its the 5.7l and th350 which i know is mechanical lol.   O2 will be in just as soon as i find the signal wire and have time to bust the old one out lol

[MuddiGGEr25]

Ok so did some more work and i installed a used 4wire narrowband heated o2 sensor from a 98 pontiac, that was working at time of pull (about 2 months ago)

I got my info from this forum since he also was using a 87 donor harness: http://67-72chevytrucks.com/vboard/showthread.php?t=352321

Ok here are all the pin outs and the color of the wires. My computer is the standard #1227747

A1- grn/wht- this wire is used to power the fuel pump-relay.
A2- no wire
A3- no wire
A4- gry- to egr-relay. This is a ground for the ECM to control the EGR relay.
A5- brn/wht- service soon light. This is a ground to turn on the light.
A6- pink/blk- switched 12v from the ignition relay.
A7- no wire
A8- ornange aldl serial data wire pin-e
A9- wht/blk-aldl pin B When jumpered to ground will set the computer to diagnostic mode.
A10- brn- VSS speed sensor signal to the computer, (This wire I will wire this to on side of a after market VSS sensor and the other wire on the sensor goes to ground).
A11- blk- MAP sensor ground.
A12- blk/wht- System ground. This wire is tied to other grounds in the harness and goes to engine ground.

B1- orn- 12v batt power ( I looked and traced down this wire on my 87 cab harness and this is fuesed I think it was a 15). I will probably use a inline fuse.
B2- tan/wht- Fuel pump signal from the relay. This one ties into several places, the fuel pump, the relay, and the ecm. When the relay is on it sends 12 volts to trun on the fuel pump.
B3- blk/red- Distributor plug
B4- no wire
B5- purple/wht- Distributor plug
B6- no wire
B7- blk- ESC signal This is the knock sensor signal to the computer.
B8- dk grn- AC signal. This tells the ECM that the AC is turned on. I am going to tie this into the ac clutch wire.
B9- no wire
B10-orange/blk- park neutral switch wire. some people say this is optional but I do not think it is because it gives a signal to the computer to give the engine a slight bump in rpm.(if you don't need it why did they put it there?)
B11- no wire
B12- no wire

C1- no wire
C2- brn- wire is not needed
C3-grn/blk- Idle air control
C4-grn/wht- Idle air control
C5-blue/wht- Idle air control
C6-blue/blk- Idle air control C3-C6 all go to the Idle air control valve plug on the TBI it's self.
C7- no wire
C8- no wire
C9- purple/wht-Starter crank signal wire. Goes to the small terminal of the starter.
C10- yel- Temp sender
C11- lt grn- Map sensor
C12- no wire
C13- dk blu- throtle position sensor
C14- gry- signal to map and TPS. ( you will see it tied together in the harness)
C15- on wire
C16- orange- This wire is tied with B1 so it is a 12volt wire

D1- brn/wht- system ground goes to the engine.
D2- blk- tied to the wires for the engine ground.
D3- no wire
D4- wht- distrbutor plug
D5- tan/blk- distrbutor bypass. This is the wire that you disconnect to set your timing.
D6- Tan- O2 sensor ground to engine.
D7- purple- plugs in to the o2 sensor
D8- D13 no wire
D14- grn- Injector plug plugs into the top of injector
D15- no wire
D16- blue- Injector plug plugs into the other injector


Assuming this is correct, and from my other searches the purple wire  (D7) I cut and spliced into in the picture to run directly to the o2 sensor should have been correct, since the other threads said to follow it out of the loom on the passenger side coming from the PCM and it was the only purple wire besides the purple/white stripe. however I could not get a voltage reading at all on my analog meter set at 2VDC or 2V AC. I tried using the pigtail i found previously but it has 12V on two of the wires and i think a crappy ground on the 3rd. And from what I have been reading the pcm should be sending .5ish V down the wire not 12V. and the o2 sensor flashes back and forth constantly from .1V - .9V.

 I do not have access to a live scanner until monday so I cannot get more detailed readings BUT when the o2 is connected to that wire, after a little bit warming up, when i try to rev to say 4000 it starts to want to die, then picks up again, then hesitates, then revs up. when i disconnect it from that wire it returns to the way it has been for months. I am wondering if i connected to the wrong wire, or if this is how it "learns" fuel trims once in closed loop.

I disconnected it just in case i was connected to the wrong wire.

I think my CEL bulb is burnt out since it did not flash when i jumped the terminals, nor does it turn on anymore when KOEO, but I cannot have the truck down long enough to change the bulb until tomorrow around noon.

I do not have the heater element wired just yet, since the bung is in the manifold before the exhaust attaches, so I was wrong about the location previously.

From what i understand a GM 3 or 4 wire narrowband is simply a 1 wire with a heater or a 1 wire with a heater and separate ground to avoid unwanted readings. And with the heater unplugged it will simply wait till the exhaust heats enough.

The pics also show what was previously in the o2 bung, and the wire i am using to carry the o2 signal, it is a 3wire household extension cord and should have no internal resistance but could be shortened a bit if needed.


I got no readings from the o2 or closed loop when connected to the 12V purple wire on the pigtail, while connected to the live scanner before the shop closed.

I am not getting a o2 code anymore after i reset the pcm.



I mainly need to know if i am on the right wire, and if i am, is the sporadic revving a sign that my used sensor is "getting lazy" and not switching fast enough?

[MuddiGGEr25]

oh and my VSS is in fact connected, I drove forward about 40ft pretty quickly and it showed my speed go 1-15mph then down again as i stopped