# 1988 Chevy Cheyenne rough Running



## mpich (Feb 13, 2003)

I bought an 88 Chevy Cheyenne 4.3 TBI. This is what I have done.
Replaced 02 sensor
replaced EGR
Replaced wires,plugs,cap rotor

Still get check engine light. Bogs when trying to take off, rough idle at stops sometimes stalls. Have had it on the Comp scope at 3 different shops. Below is a list of the latest codes. This is with the engine not running.

Prom id 2251
Trouble codes Yes
Coolant 60C 140F
TPS volts 0.62
MAP volts 4.80
MAP kpa 98.9
Battery Volts 11.7
Oxygen (mv) 450
Loop Status open
Crossovers 0
Exhaust Gases Rich
Engine RPM 0
Vehicle MPH 0
TCC-Shift Light off
TCC grounded? no
Integrator 128
Block Learn 128
Learn Control off
Idle Air Control 145
Knock Signal 0
PRNDL SW p-n
4th gear SW off
A/C Request off
A/C clutch off
Air Control SOL off
Air Switch SOL off
High Battery off
Low Battery off
Clear Flood off
Async Flag off

-------Trouble Codes-------

Oxygen Sensor Lean
Code 44

Number of T-Codes 1


So please help me figure this thing out. I have also cleared the codes after everything that i have done to the engine.

Thanks in Advance
mpich


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## wyldman (Jan 18, 2001)

I would start with a basic compression test,and check the vacuum when running.

I have seen quite a few 4.3L with low compression,do the exact thing you describe.

Other things could be a plugged cat,bad fuel pump or regulator.Have you checked fuel pressure ?

Do you have any info with it running.I'd like to see the block learn and integrator values,after it has run for a bit.


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## mpich (Feb 13, 2003)

*1988 chevy cheyenne*

wyldman

Have not done compression test, but engine was rebuilt about 3 years ago. Exhaust system is brand new. It always starts no matter if it is 30 below or not. So can't see fuel pressure but will get it checked.

I will get another print out at lunch with it running for a bit and post my findings in a couple of hours.

thanks again
mpich


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## Arc Burn (Oct 21, 2002)

Is the converter also brand new?I have gutted a few converters for friends(illeagal,i know "but you would be suprised how the packing lets loose and wedges into the outlet of your converter,i'm sure wyldman has also seen this.


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## mpich (Feb 13, 2003)

*1988 chevy cheyenne*

Not sure what you mean by converter?

mpich


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## mpich (Feb 13, 2003)

*1988 Chevy Cheyenne*

Maybe I should elaborate a little more.

Some times, usually in the morning the check engine light will not come on, it still bogs for a bit till it warms up but then will run fine with no check engine light. but if i stop for a coffee or something and turn the truck off then restart it the check engine light most likely comes on and it starts running rough again. This is when I see it the most. The truck runs good at 80-100K weather the check engine light is on or not.

mpich


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## CT18fireman (Nov 30, 2000)

Too me that sounds like it is getting a bad signal from something and the computer is trying to compensate. Likely culprits would be O2 sensor (replaced), mass air or and injector problem. I would also consider the possibility of a mechanical problem such as a bad throttle body, vacuum leak or blocked (pinched) hose. Intermitten problems can occurr when these exist.


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## Arc Burn (Oct 21, 2002)

The catilytic converter(spelling?)follow the exhaust from the engine down,somewere usually under the cab,it's uaually oval in shape,not always but it filters exhaust gases with a special packing(used to be asbestos)but this stuff can break loose,especially with your mileage,and plug the outlet restricting airflow,this will burn out your o2 sensor and IF this is what happened,you will burn it out again,this is just a possibility here,but i have seen it a couple times on high mileage trucks.


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## mpich (Feb 13, 2003)

*1988 Chevy Cheyenne*

Well took it for a burn and here are the readings i got. I took 2 printouts. First while I was driving. second while engine was in park and running

1)

Prom id 2251
Trouble codes Yes
Coolant 55C 131F
TPS volts 1.16
MAP volts 3.22
MAP kpa 69.7
Battery Volts 14.2
Oxygen (mv) 27
Loop Status closed
Crossovers 0
Exhaust Gases lean
Engine RPM 1575
Vehicle MPH 9
TCC-Shift Light off
TCC grounded? no
Integrator 140
Block Learn 162
Learn Control on
Idle Air Control 96
Knock Signal 1
PRNDL SW R-D-L
4th gear SW off
A/C Request off
A/C clutch off
Air Control SOL on
Air Switch SOL off
High Battery off
Low Battery off
Clear Flood off
Async Flag on

-------Trouble Codes-------

Oxygen Sensor Lean
Code 44

Number of T-Codes 1

And here it is in park running.

Prom id 2251
Trouble codes Yes
Coolant 85C 185F
TPS volts 0.64
MAP volts 1.34
MAP kpa 35.0
Battery Volts 14.6
Oxygen (mv) 103
Loop Status closed
Crossovers 1
Exhaust Gases lean
Engine RPM 675
Vehicle MPH 0
TCC-Shift Light off
TCC grounded? no
Integrator 123
Block Learn 153
Learn Control on
Idle Air Control 16
Knock Signal 4
PRNDL SW P-N
4th gear SW off
A/C Request off
A/C clutch off
Air Control SOL on
Air Switch SOL off
High Battery off
Low Battery off
Clear Flood off
Async Flag on

-------Trouble Codes-------

Oxygen Sensor Lean
Code 44

Number of T-Codes 1

And that's it. I was watching the cumputer as I drove and did see the Exhaust gases switch from lean to rich quite offten as i drove.

Thanks
mpich


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## wyldman (Jan 18, 2001)

Well,I doubt it's a convertor,most of the older full size trucks have pellet bed covertors,which never clog up,and have nothing to come apart.It would be worthwhile to take a look at it anyways,just to make sure.

CT18fireman had a few good points,especially a vacuum leak.They are bad for the throttle body gasket blowing out,and the PCV vacuum tube connection at the throttle body getting soft.They don't have a mass airflow on that engine though.

Judging from your last two printouts,you do have an O2 problem,or the O2 is picking up a problem.The O2 voltage is pegged low in both,and the crossovers (O2 switching across .5V) are also very low or nothing.Are you sure that your O2 wire is not grounded somewhere ? Check near the back of the head,sometimes they droop and burn on the manifold.

Next time it does it,unplug the 02 and look at the O2 voltage with the scanner,it should be .450-.500 V.If it isn't then either the ECM is bad or the wire from the O2 to ECM is grounded. If the voltage comes up to .450-.500V then the O2 is bad or you have another mechanical problem causing the lean condition.


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## Arc Burn (Oct 21, 2002)

Wyldman,what does the pellet type packing look like?The last one i cut open was a 94 dodge and it had a hard honeycomb like packing wedged tight in the outlet,just curious about the one you mentioned.


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## CT18fireman (Nov 30, 2000)

Thanks Wyldman. I do not know the exact setup and was talking more generic fuel injection / emissions problems which could cause the rough running.


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## wyldman (Jan 18, 2001)

There are two basic types of convertors.

The pellet bed style which are quite wide,10 inches or so,and about 14 inches long.They usually have a large round fill plug on the bottom,abvout 2 inches in diameter.They have a bed of platinum coated pellets,which the gases flow OVER,and the hot platinum pellets act as a catalyst to help burn raw unburnt hydrocarbons.They never plug up.Used mostly on GM products from the late 70's to early 90's

The other style is the honeycomb style.It is a platinum coated ceramic honeycomb is which the gases flow THROUGH.When the honeycomb breaks up,it usually rattles,and plugs up the convertor exit,causing a power loss.I have seen a few plugged with carbon as well.The honeycomb style uses fiberglass mats to insulate the bed of the convertor.No asbestos is used.

If the convertor is glowing red hot,then it is trying to deal with a large amount of unburnt fuel.

They also use other rare metals like rhodium,palladium,and irridium.

Most honeycomb styles can be a single stage (2 way),or a dual stage (three way).A two way takes care of unburnt Hydrocarbons (HC),Volitile organin compounds (VOC's),and Carbon monoxide (CO).A three way has a second honeycomb stage to help reduce Oxides of Nitrogen.


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## wyldman (Jan 18, 2001)

> _Originally posted by CT18fireman _
> *Thanks Wyldman. I do not know the exact setup and was talking more generic fuel injection / emissions problems which could cause the rough running. *


I know,it's hard to know what every vehicle is equipped with.We work on them every day,and I still can't remember every setup out there.I wish they could keep them all the same.


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## Arc Burn (Oct 21, 2002)

Good info Wyldman,i was not aware of that:waving:


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## CARDOCTOR (Nov 29, 2002)

one thing you can do to check o2 operation

warm it up (closed loop)

get a propane tester basicly a propane bottle with a hose 
with it running slow send the propane gas into the throttle body
until it almost stalls at this point the truck will be running real rich
look at you o2 reading should read at least 900mv if it does 
then you know the o2 sensor circuit is working properly
if not you need to check the o2 circuit
you can also run the propane around the engine if the rpm change youhave a vac leak
check vac hoses for cracksalso use needle nose pliers to pinch of vac lines if idle changes this could be your leak


cardoctor
:salute: :salute: 
the quiet before the storm


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## mpich (Feb 13, 2003)

*IN the Shop*

Well I brought it into a very reliable shop this am for them to throw it on the scope. I will keep everyone posted as to how I make out.

Thanks again to all of you.

mpich


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## mpich (Feb 13, 2003)

*PROBLEM FIXED!!!*

Well it is Fixed.

On Friday I took it to a carb shop to get it scoped. Thet looked at it all day and came up with the conclusion that my TBI had a lot of play in the center shaft, but could not guarantee that this was the actual problem. Nor could they guarentee that drilling out the shaft and adding some bushing would cure the problem.

I jumped in my truck and left another $70 in the toilet.

On Saturday I went to the wrecker and got a TBI from an 89 van already taken off and only $40. Then went to piston ring and got a new base gasket. Brought it to my shop at work and started to remove the TBI off the truck, when i noticed the TPS was totally different on the 89. Could not even swap the two due to the different bolt pattern on the 2 TBI units for the TPS.

I decided to at least change the base gasket anyway. When I took the old base gasket off there was a small hole burnt through it in on spot so it was good that I changed it.

Although it did not help!! Still bogging and check engine light.

I took back the TBI I got from the wrecker and exchanged it for an 86 TBI that looked mint no play in the shaft, the spring was really tight looked great.

Sunday back to work and readdy to swap again. Everything went smooth, started truck up like the new TBI was meant to be there.

Have had no check engine light no bogging, shifts better can barely hear the engine stopped at a red light. LIke night and day!!

So i really do not know if it was the loose shaft, TPS maybe was bad on old TBI??? Just know that it works and works GREAT.

Thanks to all of you here for your support and suggestions I love this Forum.

mpich


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## Arc Burn (Oct 21, 2002)

Now that was interesting!thank YOU for posting your results,we can all use this info in the future,too many people ask a question and get a ton of responses but we never hear the fix in the end!Although i notice the situation getting better and hey,we all have a friend or a friend of a friend who will benifit from these findings.
Good work


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