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post #1 of 56 Old 05-21-2015, 06:39 PM Thread Starter
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2.8 problems

I've got a 1987 2.8 tbi. In the last year I've replaced intake gaskets and tbi gaskets. New ignition coil, new ignition module, new cap and rotor. 6 new spark plugs. I've checked for vacuum leaks. New iac valve. New fuel pump and fuel filter. Problem now is the truck cranks and idles fine. But when I'm driving and go to stop the truck will idle low and if I'm not carefull it stalls completely. I can't figure out what it is. I also seem to have occasional misfire in my passenger cylinder bank. So I don't know if it's fuel injectors or some other part of the ignition. If I rev the truck up it will act fine again. Are the injectors suppose to constantly spray or pulse really fast?


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post #2 of 56 Old 05-22-2015, 11:57 AM
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Re: 2.8 problems

Did you check to see if there are any codes present? Not much to these truck's EFI systems. Could be the IAC stepper motor going bad or dirty. It's in the side of the TBI. Has a four wire plug on it. Square 2x2.

Anybody remember the steps for testing it?



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post #3 of 56 Old 05-22-2015, 12:35 PM Thread Starter
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2.8 problems

2.8 problems-imageuploadedbyag-free1432312445.284577.jpg
Those are my codes last time I checked. Coolant sensor is new with pigtail. So I doubt that's a problem and like I said the fuel pump is only a year old. I just replaced the relay for it too
And I replaced the egr about 3k miles ago and I replace the idle air controls valve not sure if I replaced connector

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post #4 of 56 Old 05-22-2015, 03:07 PM Thread Starter
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Re: 2.8 problems

I will test fuel pressure tonight but I don't know if it's going to be accurate because when I crank it up it acts fine. I don't notice a lack of power even running 31's. We've adjusted timing before and it always ran best with the mark of the degree plate but I could have it set wrong and it be way to lean. And our truck only have map sensors right? Could that be it? Throttle position sensor? Do you know what a meter is suppose to read on the map sensor, throttle position sensor, fuel injector wires?


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post #5 of 56 Old 05-22-2015, 04:32 PM Thread Starter
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2.8 problems

2.8 problems-imageuploadedbyag-free1432326666.322168.jpg
What is this? I can't remember. But when I unplug it idle drops and goes up when I disconnect vacuum hose and plug it back in idle shoots up for a minute. If i plug vacuum line rpm drops and if I just plug in the connector without vacuum rpm goes up too also. I've got 3 relays on the driver side 2 5 wire relays and 1 4 wire. I don't see that wire pattern on diagrams


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post #6 of 56 Old 05-22-2015, 05:48 PM Thread Starter
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Re: 2.8 problems

Alight keep in mind I was messing with the map sensor with the truck running. But now I'm pulling 13, 32, 33, 34. Messing with the map probably set those codes off. I'm not getting a o2 reads lean anymore, and I'm not getting a code 54 anymore. Should I reset the ECM and do it again? How do I reset it


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post #7 of 56 Old 05-22-2015, 07:26 PM Thread Starter
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Re: 2.8 problems

Also someone told me the round vacuum canister was just for the cruise control. So I cut the hoses and pluged them. Would that cause anything?


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post #8 of 56 Old 05-23-2015, 08:36 AM Thread Starter
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2.8 problems

Alright I reset. Now I'm only pulling a o2 code. Which I unplugged it yesterday. I'll pop the new o2 sensor in and see what happens. But the guys at autozone said a o2 sensor was almost useless on a 87 so that's why I never put it in. If it's not that it's something on the engine that doesn't shoot codes. I didn't find any vacuum leaks. And my idle air control was working fine when I tested it. It's only while driving when you let of the throttle. People are saying the torque converter could be doing it. Does anyone know where the switch or solenoid is for the tc?


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post #9 of 56 Old 05-26-2015, 06:18 AM Thread Starter
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Re: 2.8 problems

It's been acting better with the o2 sensor. Hadn't thrown any codes. Until last night when I took it up to 85(very fast for my engine). And them it threw 2 codes. 3 flashes followed by 2 and then 4 flashes followed by 4. Which I'm assuming is 32 an 44. Egr circuit and o2 reads lean. My egr valve is brand new almost so idk whats all included in the egr circuit. And I know lean could be egr, timing, fuel pump, injectors


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post #10 of 56 Old 05-26-2015, 07:29 AM Thread Starter
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Re: 2.8 problems

How do I test the electronic vacuum control valve?


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post #11 of 56 Old 05-27-2015, 06:07 AM
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Re: 2.8 problems

Reset the ECM to clear the codes.

Drive it normally and keep the speeds down for a couple of days. Pay attention to how it runs.

Just curious to see if everything is normal with normal driving.

I'm going to guess that 85 is getting close to pushing the limits of fuel pressure supply versus actual demand.

Stock PSI is about 9psi.

Repsonse is much better across the board when closer to 13 psi, but to do this, retuning of the tables in the prom are required.

Oh, don't pay attention to the "guys at autozone" and what they say, especially crap like that.

That's why they work at autozone....idiots....

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3.4l, Edelbrock intake, a 4.3l throttle body controlled by an '88 TBI ECM. 700R4 with 3.73 rear. Real time tuning using a CF-30 Toughbook with a Moates Ostrich 2 emulator.
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post #12 of 56 Old 05-27-2015, 08:00 AM Thread Starter
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2.8 problems

I did a couple days ago, the o2 helped a good bit but it still did it deceling from 45-55 on occasion. I disconnected the vacuum to the egr. I know the egr is new but I'm guessing the valve is faulty and letting to much egr. So it's been doing better the last day or two, even idling cleaner sounding. But I live where I work so on a daily basis I usually don't hit over 35 down the dirt road. Once I get the time I'll check fuel pressure, check vacuum on the intake, and probably do another tune up and adjust timing.

Could an adjustable regulator in the tbi help? And are there any aftermarket Equipment for cheap that I could tune it with?


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post #13 of 56 Old 06-02-2015, 09:19 AM
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Re: 2.8 problems

A remote fuel pressure reggy can be installed, but it is not as easy on a TBI system since the stock reggy is built into the TBI body.
Here ya go:
http://www.ebay.com/sch/i.html?_from...or&_sacat=6000

Tuning is a lot more complicated... You need hardware and software to change the fuel/timing map in the ECU. You also need to know how to adjust the maps.
There are chips available that improve the fuel delivery, they are a good improvement over stock, but are still a compromise.
Here is an example:
http://www.ebay.com/itm/Hypertech-Th...c6cdee&vxp=mtr

Good luck, if you go for any of these improvements, post your results.

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3) '90 S10 2.5, 5 speed shorty
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post #14 of 56 Old 06-04-2015, 05:08 AM
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Re: 2.8 problems

The ecm expects base timing to be set at a specific value, I.E. 1228062 ECM BINs run a 10 degree initial advance whereas 1227747 ECM BINs are 0 degrees.

1985 GMC S-15 Gypsy ext cab.
3.4l, Edelbrock intake, a 4.3l throttle body controlled by an '88 TBI ECM. 700R4 with 3.73 rear. Real time tuning using a CF-30 Toughbook with a Moates Ostrich 2 emulator.
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post #15 of 56 Old 06-04-2015, 07:54 AM Thread Starter
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Re: 2.8 problems

Whenever I took the timing down to 10btc it idled very low and would almost shut off my motor had a 15-20 degree timing plate and my timing mark isn't even on the plate anymore just slightly off it probably needs a timing chain


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post #16 of 56 Old 06-04-2015, 10:32 PM Thread Starter
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Re: 2.8 problems

Also the best gas mileage I ever got out of it was 20 mpg after a tuneup and timing it just by ear. I haven't been able to get it times right again


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post #17 of 56 Old 06-11-2015, 11:26 AM Thread Starter
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Re: 2.8 problems

Will I need a retune with the adjustable fuel regulator. Or just put at 13-15 psi and let it go


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post #18 of 56 Old 06-11-2015, 04:44 PM
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Re: 2.8 problems

You won't be able to put a regulator inline with the tbi unless you take out the regulator in the injector pod first.

1985 GMC S-15 Gypsy ext cab.
3.4l, Edelbrock intake, a 4.3l throttle body controlled by an '88 TBI ECM. 700R4 with 3.73 rear. Real time tuning using a CF-30 Toughbook with a Moates Ostrich 2 emulator.
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post #19 of 56 Old 06-12-2015, 10:28 AM Thread Starter
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Re: 2.8 problems

Yes I know. I'm just making sure the stock ecu does fine on 13-15 psi without the need to retune


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post #20 of 56 Old 06-12-2015, 11:57 AM
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Your BLM values will go rich globally. Knowing how much will be a guess without data logging.
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post #21 of 56 Old 06-12-2015, 08:24 PM Thread Starter
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Re: 2.8 problems

So I unplugged the vacuum line that runs straight from the tbi to the vacuum control valve. Idle raised a bit and it's not as loppy, but keep in mind I've had the egr disconnected. Imma see how it does. Possible a new vacuum valve


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post #22 of 56 Old 06-13-2015, 04:52 PM Thread Starter
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Re: 2.8 problems

Q2.8 problems-imageuploadedbyag-free1434228635.690532.jpg2.8 problems-imageuploadedbyag-free1434228655.189322.jpg

Changing plugs wires cap and rotor. Bent cap posts and pulled 3 wire connections out with ease when I removed the wire. Also one plug is chipped right at the center electrode. I can't find any charts though


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post #23 of 56 Old 06-13-2015, 06:24 PM Thread Starter
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2.8 problems

Another problem. In park or neutral I can ref my truck shy of 7k rpm. With the peddle to the floor overdrive or not my transmission shits around 4k, it won't go above 4k. Now I can drop it into drive 2 or 1 and get it all the way to red line. In drive 2 at 5k I'm hitting over 70mph. But even in d or od if you put the peddle to the floor it should redline before it shifts correct?

Also. I took the filter out the back of the electronic vacuum valve. Now if I've got my egr hooked and plug the tbi line into it the engine stalls immediately. If I unhook the egr all it does is idle a couple hundred rpm slower. Is that normal? At the moment The tbi line that goes to the valve is open in the engine bay, truck is idling warm at 800


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post #24 of 56 Old 06-13-2015, 09:38 PM Thread Starter
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Re: 2.8 problems

I just got done. I advanced the timing and backed it off. I've still got slight starter lag. But now at idle, if I lay on the throttle the injectors pulse for a split second like tsh tsh tsh and straighten out. But also playing with the timing. I never heard spark knock once, and I advanced it and retarded it until it cut off. Only problem was I unplugged the est and whenever I would adjust the timing the engine would speed way up for about 10 seconds both advancing and retarding


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post #25 of 56 Old 06-15-2015, 01:00 PM Thread Starter
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Re: 2.8 problems

So I timed it off vacuum. Max i was getting was about 18 inches. I backed it off to 16.5. And every time I lock the distributor down it drops back don't to 15 inches. Now it's reading about 13.5-14. So needless to say I can't time it. I drove 20 miles and burnt a quarter tank of gas. Imma throw a new distributor in it this weekend, if it doesn't fix much. Time for the 3.4. I could have already done the swap with me trying to fix the 2.8


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post #26 of 56 Old 06-16-2015, 05:23 PM Thread Starter
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Re: 2.8 problems

I am postulating that the distributor internals are shot. When I tighten it it advances the timing. I can either purposely set the Timing low and hope it messes it up enough to run right or just get a new dizzy this weekend. Either way it's got some serious detonation between 900 and 1400 rpm. Sounds like backfire out the exhuast(which I know it's not)


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post #27 of 56 Old 06-16-2015, 05:34 PM Thread Starter
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Re: 2.8 problems

Another question. When I tighten the hold down bold, I tighten it until I can't move the wrench anymore, could I be over tightening it moving the gear teeth slightly away from each other. I feel like I answered my own question, but comments would be helpful


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post #28 of 56 Old 06-16-2015, 06:14 PM
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Re: 2.8 problems

Hmmmm...not sure what to tell you. This is one of those situations where knowing if the ECM is throwing a code and/or hooking up something to view live sensor data would help.

I know on my truck, the distributor would shift slightly when tightened down.

Are you sure your not 180 out?

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3.4l, Edelbrock intake, a 4.3l throttle body controlled by an '88 TBI ECM. 700R4 with 3.73 rear. Real time tuning using a CF-30 Toughbook with a Moates Ostrich 2 emulator.
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post #29 of 56 Old 06-16-2015, 07:45 PM Thread Starter
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2.8 problems

So guess what. Brand new set of spark plug wire from advance. Apparently the last 2 days I've been running on 5 cylinders. So I won't be buying cables from them anymore. Put my old one on and it runs hell of a lot better. Still slight ping. Imma back of the timing slightly now. Also adjusted my tv cable and it shifts like its suppose to, at least I can hit 5500 rpm now. Nah I've always been careful putting the dizzy back in, that was the one part nobody could touch.
And it doesn't throw codes anymore since I blew out the vacuum valve for the egr.

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post #30 of 56 Old 06-16-2015, 08:10 PM
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Re: 2.8 problems

That's awesome.

1985 GMC S-15 Gypsy ext cab.
3.4l, Edelbrock intake, a 4.3l throttle body controlled by an '88 TBI ECM. 700R4 with 3.73 rear. Real time tuning using a CF-30 Toughbook with a Moates Ostrich 2 emulator.
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post #31 of 56 Old 06-16-2015, 09:13 PM Thread Starter
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Re: 2.8 problems

For the most part it's running better. Still have some starter drag. But it's not knocking of half 87 and half 92 in the tank. I'll have to further adjust it once I get a vacuum gauge


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post #32 of 56 Old 06-17-2015, 10:55 AM
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Re: 2.8 problems

I hope you don't mean that you are going to adjust the timing.

The ecm expects the initial timing to be at 10 degrees. All of it's timing is based on that.

1985 GMC S-15 Gypsy ext cab.
3.4l, Edelbrock intake, a 4.3l throttle body controlled by an '88 TBI ECM. 700R4 with 3.73 rear. Real time tuning using a CF-30 Toughbook with a Moates Ostrich 2 emulator.
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post #33 of 56 Old 06-17-2015, 11:26 PM Thread Starter
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Re: 2.8 problems

I might be able to get it back to ten. But I'll have to find and remark the balancer at TDC.


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post #34 of 56 Old 06-18-2015, 01:23 PM Thread Starter
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Re: 2.8 problems

Imma replace the timing chain and fuel injectors this weekend.

Does anyone know if the comp cams timing chain is a good chain


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post #35 of 56 Old 06-19-2015, 09:32 PM Thread Starter
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Re: 2.8 problems

So I did correct the timing to 10 Btdc. And I still have a miss especially noticeable at low rpm and in OD


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post #36 of 56 Old 06-19-2015, 10:55 PM Thread Starter
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2.8 problems

So it's still at 10 degrees. So it's not jumping timing, I'll test the ignition components with an ohm meter tomorrow. For some reason I think it's fuel related. Still having the injectors pulse if you suddenly open the throttle
And it's not throwing codes

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post #37 of 56 Old 06-20-2015, 06:52 AM Thread Starter
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Re: 2.8 problems

So if also got a new distributor. Is there anyway to verify the distributors inner components are good without taking it out of the engine? If it's good imma return the distributor I bought. Also is it normal to be able to move the rotor button slightly when the cap is off


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post #38 of 56 Old 06-20-2015, 05:46 PM Thread Starter
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Re: 2.8 problems

An now my motors idling at 1000 rpm hot. So smh.


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post #39 of 56 Old 06-20-2015, 09:01 PM Thread Starter
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Re: 2.8 problems

Could it be dead spots in the distributors pickup coil? Or something like that


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post #40 of 56 Old 06-21-2015, 08:22 PM Thread Starter
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Re: 2.8 problems

So I'm sure I figured out what it was. I had a major vacuum leak at the tbi test port. Got that straightened out, changed all the vacuum hoses, fuel filter. So I'll be test driving soon. Also got some blue led driving lights hooked up, and some off-road lights


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post #41 of 56 Old 06-21-2015, 11:28 PM Thread Starter
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Re: 2.8 problems

So high idle is gone. Still misfiring. Popped the hood tonight, my number 1 spark plug/wire is arching to the block. Gonna wait for the motor to cool down and go inspect. If I have another bad plug wire I'll be pissed


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post #42 of 56 Old 06-22-2015, 09:58 PM Thread Starter
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Re: 2.8 problems

So no more arcing. Still misfiring. I've got ticking noise from cylinder 4 both down near the plug and at the valve cover. Could be bad valve springs/miss adjusted valves.


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post #43 of 56 Old 06-24-2015, 04:20 AM
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Re: 2.8 problems

"T" in a vacuum gauge somewhere in there and watch what it does while idling.

1985 GMC S-15 Gypsy ext cab.
3.4l, Edelbrock intake, a 4.3l throttle body controlled by an '88 TBI ECM. 700R4 with 3.73 rear. Real time tuning using a CF-30 Toughbook with a Moates Ostrich 2 emulator.
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2.8 problems

The needle vibrates back and forth by about a inch of vacuum. It's got me stumped because my tps and map checked out good. I pulled and checked all my plugs they look good. All wires check out good from visual tests and testing with an ohm meter. I guess I need a compression test. I would think it if was bad valves it would act up regardless of what rpm. But it's only at rpm below 2k that you notice. If your in overdrive, sometimes it gets so bad it constantly kicks the transmission in and out of overdrive with the pedal steady
Would teeing in a vac gauge and watching it will I drive tell me anything? You don't notice the stumble at idle to much except for the occasional dull sound from the exuast

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post #45 of 56 Old 06-25-2015, 09:12 AM Thread Starter
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Re: 2.8 problems

It wouldn't be so bad. I get 160ish miles a tank road driving. Problem is it does it worse at near idle speeds. And that's the range it drives at 80% of the time. All this week had been farm driving under 25 mph. And I got 40 miles out of 3/4 of a tank


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post #46 of 56 Old 06-29-2015, 11:20 AM Thread Starter
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Re: 2.8 problems

So it's doing alright. It smokes on startup every now and then. Also got a decent gas smell out of my crankcase. I ran a pressure test on 4 of my cylinders and got between 100 and 120 psi. Though I wast sure how long to crank it over, I was getting different readings unless I cranked it for a few seconds


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post #47 of 56 Old 06-29-2015, 01:35 PM Thread Starter
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Re: 2.8 problems

So I found 95 3.4 over at tacreationsusa. 135k miles. I'm heavily considering that, and a moderate rebuild for at least gaskets and seals


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post #48 of 56 Old 06-29-2015, 02:40 PM
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Re: 2.8 problems

We are more than happy to help you with that build. A lot of stuff can be found in my build thread and the 3.4 sticky! How much for motor?



1984 xcab s-10 3.4L GM crate engine 91 S10 TBI swap w bored intake, Edelbrock headers. 2" Rough Country Lift. Flowmaster, shift kit, e-fan.
The S-5 trailer-Half a 1st Gen LWB S-10


EFI swap https://www.s10forum.com/forum/f106/...e-help-513616/

My build thread (3.4L)https://www.s10forum.com/forum/f106/...stions-427168/
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I had to cut my nut in half .
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post #49 of 56 Old 06-29-2015, 02:48 PM Thread Starter
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Re: 2.8 problems

They want 450 for it. They had other ones for 200 but they were either high mileage or smoked.


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post #50 of 56 Old 06-29-2015, 02:49 PM Thread Starter
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2.8 problems

The the 2.8 flex plate and transmission assembly bolt up directly to the 3.4?
A manual tranny would be in it's future but for now the cheapest option would be my tranny, and mine had seemingly no issues

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