First half-throttle stumbling, now WOT stumbling

[Jimmy]

Check the wires running from the coil to the back of the distributor and connected to iginition module. They are pink and white in color

Chip not seated properly

Loose or chafed wires going into ECM

Loose or bad grounds (2 on the engine 1 under the tailgate)

Vacuum leak

 

[sytydvr]

pull out a few spark plugs how do they look? smell ?

what is your base fuel pressure?
if its not your ignition is definately fuel related maybe clogged fuel filter? or fuel pressure too high

keep us updated

 

[myclone]

Need to know the following:

What NGK plugs (part #)?
Plug gap?
What is your base timing (need to unplug the "set timing" connector)?
What is your base FP with vacuum line disconnected and plugged off?
How many miles on the truck?
Verified TPS action with an analog volt/ohm meter looking for "dead" spots?
Verified vacuum line to MAP sensor is good?
Verified correct part # GM 3 bar MAP sensor?
Verified grounds on back of passenger side cyl head are clean/in tact?
Verified grounds at ECM?
Verified correct battery voltage at ECM (low voltage is common and causes numerous probs)?


Your probs could be any number of things related to the above or not. Happens all the time with these trucks. Ive seen the grounds I mentioned above that are located on the back of the pass side cyl head wipe out an ECM. Changing ECMs fixed the problem temporarily until the other ECM died cause we didnt check the grounds to see if that was an issue. What Im getting at is just because you fix the symptom doesnt necessarily mean you fixed the problem and it will come back to haunt you sooner or later... So, EVERYTHING needs to be gone over on these trucks... ESPECIALLY if you have one that someone has modded/tinkered with.

HTH..

Oh, newbs usually get flamed so dont take it personal. They ask questions, get answers, dont like the answers, do things "their way", and then when the truck is still FUBAR they come back saying "hey, it was a bad plug wire or whatever". Happens all the time so the OG ppl are gonna pounce on the newbs. Again, nothing personal but it happens a couple of times a month at least.

 

[Black Storm]

Thanks for the help guys. I printed out this page and we will go over everything again tonight after work. I'll post this evening and answer some of your questions as well.

myclone - I understand. I'm sure you guys get tired of the newbs asking for help and then doing it their own way, only to find out you all were right in the first place. I know that you guys are the experts here, not me.

I'll post again later this evening. Thanks again.

 

[cloneman315]

dont take it personal they hate me 2 but some r trying to help lol but get a wire diagram and confirm all your grounds at the ecm r good and the ground straps of the heads r tigt.And also the ground on the intake on the drivers font bolt.Ps mine did the same thing turns out it was a bad ground i found this by using the schematic for the ecm plugs.

 

[ed hess]

myclone

The most interesting thing i find here is

>>>Verified TPS action with an analog volt/ohm meter looking for "dead" spots? <<<

I dont think anyone has ever mentioned anything on this bbs about looking for "dead spots"

Very interesting! Have you seen this occur?

ed

 

[myclone]

myclone

The most interesting thing i find here is

>>>Verified TPS action with an analog volt/ohm meter looking for "dead" spots? <<<

I dont think anyone has ever mentioned anything on this bbs about looking for "dead spots"

Very interesting! Have you seen this occur?

ed

Yes, many times actually.. Needless to say I get questions from ppl at work/neighbors about their vehicles and what to do to fix them. Depending on the symptoms the TPS test might come into play. On Monday I had a co-worker with some probs on his wifes ford escort (well, more probs other than its a ford escort) and it turned out the TPS had a worn/dead spot in the just off idle location. It caused all kinds of drivability issues but never threw a code. I had him test the TPS with an analog meter to verify it was linear throughout the TPS actuation and thats how we found the "dead spot".

FWIW.. A TPS is just a potentiometer (same as a volume knob on an old school stereo) that increases or decreases resistance as its actuated. If there is a lot of miles on a vehicle the TPS can and does wear out in the first ~1/4 of its travel where 90% of the day to day driving takes place. This can send wacky info to the ECM as it may think you are opening the trottle more/less than it actually is. To test it just hook up an analog volt/ohm meter across it and rotate the throttle slowly by hand from closed to WOT and watch the meter. If the needle on the meter fluctuates any then you have a TPS that needs replacing. The needle on the meter should slowly but steadily move from low resistance to high resistance (or vice versa depending on how you hooked it up) without any fluctuation.

That splain it?

 

[myclone]

Oh, yeah... One more thing... Be sure to use an analog meter (the ones with an actual needle movement) instead of a digital. The analog is the only way for us humans to really see any fluctuation as a DVM (digital volt meter) is way too fast which makes it tough to make sense out of the numbers changing at such a fast rate. An analog makes it 5 kabillion times easier to see and you can get a cheapy analog for a couple of bucks. at anywhere from walmart to radio crap...er....shack.

 

[Black Storm]

Need to know the following:

What NGK plugs (part #)?
Plug gap?
What is your base timing (need to unplug the "set timing" connector)?
What is your base FP with vacuum line disconnected and plugged off?
How many miles on the truck?
Verified TPS action with an analog volt/ohm meter looking for "dead" spots?

Here's a few answers to your questions.

NGK plugs are UR5 #2771
Plug gap is .035
Base timing was "0"
Base fuel pressure was 50
Truck has 110k miles
There were two TPS dead spots and that has been replaced

The truck runs better. When the engine is still fairly cool, the truck doesn't stumble at all and the boost maxes at 16 psi like it should. But once the truck warms up, the truck still stumbles under half throttle and WOT throttle and only showing 14 psi max. We are going to work on it again tonight.

 

[myclone]

Runs good cool but runs like ass hot.... If I had that truck in my garage those symptoms would tell me to go after a fuel delivery issue first. Fuel delivery includes everything from the fuel pump to the ECM to the injector wiring harness (IMO).

When cold the ECM runs in open loop which is basically the carbed version of having the choke on (rich mixture). Once up to temp the ECM switches to closed loop which leans out the A/F ratio using the feedback info from the O2 sensor (along with some others). So, that being said Id start checking the O2 voltage via a scan tool to make sure the cross counts were good. That would possibly give you a hint to whether the truck was rich or lean.

Reading the plugs would help but there seems to be a shortage of ppl that can or will do that.

Anyway... Your problem could be anything from a bad memcal/ECM to problems with the physical fuel delivery system (pump, lines, injectors, ect). Then again it could be totally unrelated to fuel delivery as its tough to fix stuff over the net. I usually have to put my eyes, ears, and hands on it.

 

[Black Storm]

Thanks for your info. I met up with some Syclone guys last night. One of them had problems that were similar to mine. He replaced his fuel pump and it still did the same thing - he found out it was the fuel sending unit that was bad. One of the guys had datamaster but he didn't get a chance to hook it up to my truck. I might have an opportunity to hook up a scan tool this week.

When I left the Sy/Ty get together and my truck was cool, I pulled out onto a two lane road and I saw an S-10 with a carb stickin through the hood coming up on my right. He looked over at me and smiled and slowly passed me. His back wheel was at my front wheel and I hit it. Once he heard me hit it then he punched it. I pulled him about 5 or 6 cars and my truck felt great. No stumbling or black smoke or anything. I slowed down and the guy was like "DAMN that thing is fast!" but then about 10 minutes later during my ride home I punched it and it ran like crap.

 

[Black Storm]

Also something I noticed -

Right now the truck is running great while it's been running for 5 minutes, but after about 10 minutes it hesitates and stumbles. I noticed that I can shut the truck off for a few minutes and then start it back up and even if the engine temp is the same the truck won't stumble - it will run fine. But then after another 10 or so minutes it does the same crap again.

One more thing - once the truck starts stumbling - I noticed that it will never do it at 12 psi or under. It starts happening around 13 - 14 psi and above.

 

[Buster]

You live in Minnesota, I know a few guys in Minnesota that own syty's, might try getting datamaster and weeding out the problems instead of posting a hundred different symptoms. I'm not ripping on ya either, I just have a good idea of how this stuff works.

 

[Buster]

In fact I know where you can get a laptop, diacom and the cable for $150, guy lives in Coon Rapids, really a nice guy and extremely sharp.

 

[Joey Allen]

If you haven't tried the dark spot spark check I would recommend that. I too had this problem and like you had just replaced everything under the hood. Cap, rotor, plugs, vacuum lines and ATR wires. Mine stumbled just like your saying, but with no black smoke or WOT stumble. I thought NO WAY could this be happening all parts are new, but low and behold the # 3 plug wire wasn't snapped on the plug good. Popped it on good and 90% of the stumble was gone. And not to mention ATR plug wires do ark if to close to one another. Now I intend on replacing the fuel pump with a better one.

"When in doubt try the craziest thing, it might just work"
'92 Ty 1635

 

[Black Storm]

You live in Minnesota, I know a few guys in Minnesota that own syty's, might try getting datamaster and weeding out the problems instead of posting a hundred different symptoms. I'm not ripping on ya either, I just have a good idea of how this stuff works.

Yep I was going to try that next. It's probably pretty tough to determine what the problem is over the internet when you can't even see or hear the truck. :wink: I would be very interested in the laptop, diacom, and cable

Joey Allen - I have tried that, but I might as well try again.

 

[Buster]

You live in Minnesota, I know a few guys in Minnesota that own syty's, might try getting datamaster and weeding out the problems instead of posting a hundred different symptoms. I'm not ripping on ya either, I just have a good idea of how this stuff works.

Yep I was going to try that next. It's probably pretty tough to determine what the problem is over the internet when you can't even see or hear the truck. :wink: I would be very interested in the laptop, diacom, and cable

Joey Allen - I have tried that, but I might as well try again.

You can bring the truck over this weekend, we'll take a look at it.

Later

Mark L
11.0 @ 122

 

[Black Storm]

Just hooked up a fuel pressure gauge and took the truck out. Did not disconnect the vacuum.

Base FP was 40 - at WOT FP went up to 64 max. Truck ran great - about 10 minutes into the ride it started stumbling again. Despite the stumbling, FP still maxed around 64 and stayed steady.

You can bring the truck over this weekend, we'll take a look at it.

Later

Thanks Mark.

I was the one with the Ty at Porky's Saturday. Nice to finally see your truck I've been hearing so much about.

Have a good one,

Patrick

 

[sy1907]

Patrick, ya get this shizzbang fixed yet? Lemme know, might have some time this weekend for DM if you and ML didn't hook it up.

 

[Black Storm]

Patrick, ya get this shizzbang fixed yet? Lemme know, might have some time this weekend for DM if you and ML didn't hook it up.

Yeah we got the ol shizzbang fixed. It's running pretty damn smooth now.

I plan on taking it to Rock Falls on Sunday since it will be the first time the truck has run right since June and also since I think I know how to drive the damn thing........ :wink: