'88 W100 318/2 barrel throttle body surging extreme loss of power, please help!

Discussion in 'Engine & Performance' started by nikwho, Nov 28, 2018.

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  1. nikwho

    nikwho Member

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    Hello all,
    I've searched and read, and read. But, I'm still stumped. I don't want to just throw parts at it. So, this is my 17 year old sons truck. He bought it from my wife's dad. It's a really cool short bed 4x4.

    So, at first, my son called me and said that his truck wouldn't start one cold morning. Then, he'd get it to start, but ran super rough. He pulled the air cleaner and noticed that only one fuel injector was spraying. We pulled them both out and one functioned well with power applied, the other immediately started smoking and did not open. So, we replaced just the non functional injector. My son was super anxious to get it together, so he reassembled while I was at work.

    It fired right up, but was underpowered. I realized that we had not replaced the fuel filter. So, I asked him to swap that out, which he did.

    This is the point where we could have easily determined if we were good to go, BUT, this is also where he got impatient and began to pull his stock exhaust system off and install a set of headers that we bought him for his birthday. He is very mechanically inclined, and in his third year of auto shop in HS. He didn't realize that if we had issues, it would make it harder to determine our problem.

    Anyhow, he got the headers installed, I helped him weld an O2 sensor in the header collector, and we welded up a dual exhaust system. No Catalytic converter! We cut the wires for the one upstream O2 sensor and extended them, as the factory manifolds had the o2 sensor higher up in the system. But, sensor is installed.

    Truck fires right up, but surges and hisses, stalls and backfires. Just runs like crap. I just ordered a new o2 sensor, as I think that the current one may be original to the truck. We ha to spray some PB blaster on the inside of the manifold to get the sensor broken loose. Not sure if that's hurt it. So, going to replace o2 sensor to see if that helps.

    This has a non-vacuum advance distributor. The time was off a little (I warmed it up, unplugged coolant sensor & timed it to 10 before TDC). I still worry that it may have jumped a timing gear tooth, but would I be able to time it correctly if it had?). It doesn't seem to have a misfire, though I am thinking that a new cap, rotor, plugs and wires are in order.

    I have also replaced all vacuum lines, using the Haynes manual to follow each line. It was a mess. Like, I'm surprised it ran, in the state that the vacuum lines were in. So, those are all new. I unplugged the throttle position sensor and it ran worse and would immediately die when I would touch the throttle.

    Also, this truck doesn't have a Check Engine light, the best that I can tell! I tried to read the codes with the key on/off/on/off/on method, but realized that I didn't see a check engine light when I turned the key on. So, I took the dash apart and pulled the instrument cluster. It has a "Maint Req" light (I've read it serves as a reminder to check emissions, but isn't an error light), Oil Pressure light, and right where I thought that the check engine light would be, there is a "Gate Open" light, I'm assuming would be for a Ram Charger. It had a fourth light, but I'm forgetting what it was at the moment. Anyway, I removed all bulbs, verified that none of the four lights were Check/Service Engine lights and swapped the bulbs with known working gauge light bulbs.

    So, how can I check codes in a Pre OBD-II truck, that doesn't have a check engine light? I'm stumped. I'm thinking that maybe the gauge cluster was replaced at some point?

    I'm stumped, feeling like I'm not very competent and would greatly appreciate any help that could be offered! I don't really want to take this to a shop. I would like to walk through the diagnosis of it with my son, for a teachable moment.

    Thanks so much,
    Nik
     
  2. nikwho

    nikwho Member

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    Sorry for the novel! I just looked at it after posting and realized how long it had gotten!
     
  3. crazzywolfie

    crazzywolfie Senior Member

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    the check engine light is on the panel above the heater control. it may have a burnt out bulb since it comes on everytime you start the vehicle.

    did you make sure to order a ntk o2 sensors? o2 sensor can be a nightmare to change on these thing. i used a pipe wrench on my 93 and thought i thought i was going to break it trying to get it out. i don't know if it would be the same on 88 as it would be on 89 but i think they did originally planned on putting the o2 sensor in on the y pipe after where the 2 pipes meet which is why there is a o2 sensor plug somewhere on the passenger side of the engine with an extension cord plugged into it to run back to the drivers side manifold.

    20181128_152703.jpg
     
  4. nikwho

    nikwho Member

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    Thank you so much for the reply! And for showing me where the check engine light is! I had watched a video from probably a different year truck that showed the service engine light on the dash! I was super bummed when I couldn't find it. So, I'll pull the dash back apart and replace the check engine light bulb! That will allow me to finally get some codes out of this thing! That may tell us a lot.

    Okay, we have changed the o2 sensor. Idled rough for the first few minutes, but then cleared up, as I kind of expected. I was excited and went to pull it out of the side yard, and into the drive way and realized that it had a pretty extreme lack of power.

    I had to feather the throttle between a very fine line of trying to get it to move, and dying! If I have it just a hair too much throttle, it would die!

    We have replaced the fuel filter as well. Also went through the throttle body, cleaned, replaced one of the fuel injectors and put back together. Both fuel injectors are squirting what seems to be equally.

    So, I feel like the issue is with a sensor. It doesn't feel like it has a misfire. It runs smoothly at idle and at higher RPMS when not loaded. It bogs and will die almost before it moves in drive or reverse. It revs strongly in neutral, too! It seems as though something is conflicting when under a load. Like, a bad sensor. I was thinking the Throttle Position Sensor was a culprit. When the truck is sitting and idling nicely, if I pull the TPS, the truck will die right away. Not sure if that tells anything. Truck dies immediately if I pull the vacuum hose off of the EGR valve. Again, not sure how indicative that is of anything, or if that is a normal finding?
     
  5. crazzywolfie

    crazzywolfie Senior Member

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    unplugging sensors can cause also sorts of weird things to happen. it almost sounds like a TPS in some ways not not others. i am pretty sure you can test the TPS with a mult meter to see if it is operating properly.
     
  6. nikwho

    nikwho Member

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    I thought the same thing. It sort of acts like a TPS, but not really exactly what I'd expect a failed TPS to do. I don't want to just aimlessly throw parts at it. I just started a 48 hour shift at work, so I won't be able to mess with it again until Sunday. I may price out a TPS and if it's not too spendy, I may just replace it, as I have read about a lot of trouble coming from those. I'm all for throwing parts at it that commonly fail, just to potentially prevent future issues.

    Nik
     
  7. DustyDog99

    DustyDog99 Member

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    An easy way to check if you have skipped tooth on the timing is to bring it to top dead center on the timing marks and see how far off the rotor is. The way it sounds, I believe it is a timing problem. How many miles are on the truck?

    Sent from my SM-S727VL using Tapatalk
     
  8. nikwho

    nikwho Member

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    158,000 on the clock. Not too high. So, I timed it to 10 degrees BTDC with a timing light and coolant sensor unplugged, after warming up. It took just minimal adjustment to get it there, like 2-3 degrees worth of adjustment. Would you still be able to get it timed successfully if it jumped a tooth? I have no idea. I would think you would, but the cam and valve timing would just be off. It honestly seems to run to well in neutral for the timing to be off enough to take virtually ALL power away in gear. It just feels like a sensor, with the way that it's acting. But, I honestly have no idea!
     
  9. nikwho

    nikwho Member

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    I want to make sure that I'm thinking of this correctly. So, you're saying to get a cylinder (say, #1) to TDC on the compression stroke, then verify where the rotor is pointing. Where the rotor is pointing would directly correlate to the flashes of a timing light, so it seems that this procedure would tell you essentially the same thing that a timing light would, which in my mind is the timing of the distributor to the crankshaft. If a timing chain slipped a tooth, it would lose the timing associated with the camshaft, which also is what drives the distributor. So it seems that either test would show the same results.

    Now, I JUST remembered from thinking this through, that the truck was actually showing more like 25-30 degrees BTDC when I initially checked with a timing light, so the couple of degrees that I gave in my previous post is incorrect! That bigger discrepancy tells me that it could have jumped a tooth! I was able to adjust the timing back to 10 degrees BTDC. So, that would make just the cam off, which could definitely kill power! I would expect it to run worse being off that much.

    How do these engines run when jumping one tooth? Guess that it might be a good time to grab a timing set! Do these engines use Hydraulic flat tappets, Or were they roller lifters by 1988? Might be a good time to get a mild "RV" type cam, new lifters and a timing set. If I'm going in that deep, might be worth a cam swap.

    Hmm.
     
  10. crazzywolfie

    crazzywolfie Senior Member

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    if the engine is factory it should have a roller cam. also since it is TBI you can't change the cam in it because the computer would not know what to do.
     

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