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Discussion Starter · #1 ·
I am having a problem with the truck missing/hesitating mostly at highway speeds, but it will do it moving slower as well. In the first mile or two it will run fine but then the missing starts. It was showing all of the symptoms of a fuel pump starting to fail so I replaced it since the it was still on the original pump. Got all of that finished and its still doing the same thing. I pulled all of the plugs and they look good. Finally as a last ditch effort I popped out the plug on the cat and emptied it in case it was a clogged converter causing the problem.

Also I had the the ignition control module(original gm) tested and it tested good, although I'm skeptical.


This weekend I replaced these things
fuel pump and 1/3 of the fuel lines(Bosch)
fuel filter
IAT sensor (different issue but nonetheless)
emptied the cat

In the past year Ive replaced the plugs(platinums), wires, cap,
rotor, pcv, air filters, breather, all vacuum lines. I only use premium grade standard/bluestreak tune up parts, no junk.


Is there anything that can cause this type of problem besides the obvious fuel/air/spark? Ive heard of various faulty pressure sensors etc in other makes of vehicles causing them to run oddly.


Thanks
 

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DUP post................
 

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most of the time when i see an engine doing this very thing its been because of a sparkplug wire leaking voltage into a metal part of the engine

such as at spark plug boot

check when dark out engine running look all over wires and ends for a spark leaking out of a booth etc

try with engine RPM up higher too

they like to leak mostly when under load, driving etc.

but fine at idle etc

seen it happen many times

most recently happens to be on a 90 2.5L and it fooled us good for a few days

we replaced FP and CS and such and i finally caught a glimpse of a leaking spark out of one of the wire boots at the cylinder head

a set of new wires and it was like brand new again

the wires werent original and they looked 100% fine

never woulda guessed they were doing it

cheap wires i guess
 

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Discussion Starter · #4 ·
Sorry about the double post,

I will check the wires tonight, I would hope they would still be good as new as they are, but stranger things have happened.

I was brainstorming last night and the 2 things Ive never replaced are the coil and the control module, Ive never known anybody that replaced a coil that was actually bad though.
 

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Again..... EGR...... pull the vac line off and plug it. Test drive, if better, try cleaning the thing.....
 

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Discussion Starter · #6 ·
I tried the egr thing, didn't make any difference.
 

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Having the same problem here. We just picked up this 88 S10 and it drove fine when we brought it home yesterday and last evening. But today it started to buck and chugg except under load. Not good, the whole drive train is getting hammered. Once it starts it will do it even at idle, surging rapidly, vroom, vroom, vroom, vroom very quickly. Really seems like a fuel problem.
It starts good, idles good, pulls good. It runs fine till warm, then starts to act up. Put methyl hydrate in the fuel when first got it. Tried putting some fuel system cleaner in the gas today. So darn cold out right now, too cold to spend a lot of time on it.
Getting an oil change and will get the fuel filter changed then too.
Supposed to have a faulty speed sensor on it, according to the seller. Will have to check into that.
Will also check the plug wires.
 

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why would you put platinum plugs in? get OE plugs.
 

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Discussion Starter · #9 ·
I got platinum because I never want to change them again.
 

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What brand of platinum plugs did you use? Last batch of BOSCH I put in were CRAP (I think the last couple actually were crap), I ended up putting in a set of NGK's and no more missfires.
 

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Discussion Starter · #11 ·
I think they were Autolites if I remember correctly, I've always used them in the past with no problems.

I changed the coil because it appeared to run better after I wiggled the original one around and upon inspection the plates were starting to de-laminate and the windings were loose, Still having same problems.

I also checked wires and cant see any arching, but since it does it on the highway I cant really see them when the problem is occurring.

I have noticed the problem comes and goes last night on the highway. One moment its running horrible and then it smooths out and I can floor it and it runs great.

The only things that haven't been changed are the control module and the hall effect sensor.
 

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I have always used Bosch, lately had trouble with them.

The Coil sounds kinda suspect......

Check the connections for the module and coil and everything.....
 

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Discussion Starter · #13 ·
Well, the problem ended up being the control module that originally tested good, I swapped in a spare I bought just in case and took the old module and tested it again and this time it failed, I took it out on the freeway and it ran better than it ever has since I've had it, It could be the module has been failing for a long time, or the msd coil I replaced the original with. Probably a combination of the two.

Unfortunately I still have a problem with it being hard to start when the temp drops into the 30's. But at least I don't feel like its going leave me stranded in the middle of nowhere.
 

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Check the CTS..... use the link in my sig, compare the unplugged sensor ohms in your thermostat neck to the chart.......
 

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Discussion Starter · #15 ·
I checked it and it was approximately +/-200 ohms compared to the chart, Is that enough throw it off to keep it from starting? I replaced the air temp sensor and it was 1000 ohms less than the one I replaced it with.
 

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Hmmmm, Might try putting a charger on it before you start it up in the morning, see if it starts better, your battery could be weak.
 

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I got those damn Platinums of every brand and my 2.5 ran like hell... Replaced them with the AC Delco factory plugs and all the bucking/heaving/missing shit stopped..
Just a thought..
willie
P.S. ALWAYS keep a cheapo module in the ol' glovebox!;)
 

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Hello everyone. I hate to high jack but I all so hate to start a new thread for the same problem. I am also missing at speed( real hard POP POP POP) until I get of the throttle and cut back on the power. I am going to try a timing adjustment and see if that does it. I all so have a REAL hard time starting in the cold(30f and below). I have tried everything. New map sensor, engine coolant temp sensor, fuel pump relay. I am doing the fuel filter tomorrow. Can anyone give me some incite as to why its sooo hard to start in the cold morning. It is driving(or not driving) me crazy!:eek:.

I am planing on changing the whole distributor out after the Christmas break( its the original). I would really appreciate any help and advise you have.

88, 2.5 5 speed manual.

Ben Mc Us army
 

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Check the CTS in the water neck with an ohmmeter, compare readings to link in my signature for appx coolant temperature.
 

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Discussion Starter · #20 ·
I've noticed that running premium greatly improves the cold starting problem with mine, I'm thinking the timing is too far advanced, It runs strong after it warms up.
 
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