RPM's Surging

[rover12]

Anyone help me figure out whats going on here. I have an 89 classic with these symptoms:
With the vehicle at normal operating temp. and when coming to a stop or while at a stop, the RPM's increase to 900-1000 and other times, the RPM's drop to 500-600. When RPM's drop, the truck has weak acceleration(the gas must be depressed about 3/4 of the way before the RPM's increase, but then acceleration is weak or non-existant). On occassion, while coming to a stop, the RPM's surge from 1000-1500, but this usually goes away once the truck is stopped. Another mention: All of this happens after driving from 15-20 minutes, never directly after startup.

 

[Clay]

I had a similar problem. When coming to a stop after driving at highway speeds my engine would rev in a pulsing fashion. I removed the stepper motor, gave it a good cleaning with carb cleaner and reinstalled. Problem Solved.

Also, check out www.rangerovers.net

 

[Black Mustache]

Clay is on it- check your stepper and have a good look at your timing and all things realated (cap, rotor, plugs, wires)

gl

 

[rover12]

Thanks much. Will the stepper motor set off the EFI light? I'm cleaning the stepper motor now and look forward to seeing if that will help.

 

[Chris-St Louis]

Surging.

I had the same problem. More so when I converted to a MSD ignition over the Crap OE rover Overheating ignition.

After looking at the alternator output on a scope, it looked just like a spark plug firing.

Turns out Rover routes the alternator to battery cable RIGHT under the spark plug wires.

Real Smart! The plug wires creates induction and makes the alternator to battery signal dirty like you can't beleive.

The fix is running a new cable from the alternator to the battery behind the engine. Instantly cured the problem, and other odd electrical gremlins I had. I wish I did it right away. Try that. It was cheap.

 

[p m]

Chris, I believe it's an urban legend. You may have disturbed something else that fixed your problem - or you have issues with alternator wiring.

Rover12: There are too many components that will make this shit happen. from the top of my head -
- stepper motor (AKA IAC solenoid)
- vacuum leaks
- ignition misfire or cross-fire
- poor electrical connection in the fuel injector harness.

Stepper motor - ask for that for an 89 Chevy Astro, 4.3V6. About $35 in any parts store (thanks rangerovers.net for the tip).
Vacuum leaks - easy to chase with the vac gauge. The engine should pull steady 17-22 inHg of vacuum at idle.
Ignition issues - less easy to troubleshoot; prepare to spend about $50-100 without noticeable effects.

Now, what I found very consistent - small coolant leaks from the connections of the heater hoses make their way into the fuel injector electrical connectors. Pop them up and see if any of the pins look dark and corroded. If so, clean up well with some electrical contact cleaner and soft brush, and think of something to prevent that from happening again.
This is very easy to troubleshoot - once you disconnect the big-ass connector from the ECU (under the front passenger seat). Resistance between pins 2 and 13 (IIRC) gives you the idea of how well is the connection to the injectors (right bank). Haynes manual for RRC has a good description of the procedure.

 

[p m]

Also - faulty stepper motor is unlikely to set the EFI light, but the faulty injector can and eventually will.

 

[montoya]

could be mass airflow meter

had similar symptoms where it would come close to stalling at stops. my mass airflow meter was replaced and surges stopped

 

[Chris-St Louis]

Urban Legend?

Are you kidding? Do you know about induction/Spark noise? How do you think your timing light works by just clamping a clamp on it?

And, you cannot argue with a scope.

The thing was making spikes of 2+volts going back to the battery. It solved the problem instantly, I'm telling ya.

Dont beleive me? Try it.

http://en.wikipedia.org/wiki/Electromagnetic_induction

Now, take the formula and enter 50,000 volts going through the wire.

In fact, when I disconnected the field, it ran fine, which is why I looked at the signal.


Oh course, I could have always looked in Rangerovers.net and just threw some parts at it....That would have got it for sure.

 

[p m]

Chris, as my luck would have it, I have a master's in EE.

What I am saying is that you should not have any large spikes on the 12V circuits from ignition - if you do, something is wrong.

The scope? wonder which scope did you use, and which leads. I am very reluctant to trust nearly any scope _UNDER_ $10k and fully-aluminum enclosure, and completely shielded leads, for any pulse measurements.

Oh, by the way, 50000 volts have nothing to do with induction, or your ignition setup. I wonder which formula do you refer to for 50kv to substitute to.

 

[Chris-St Louis]

I really have no desire to get into a pissing contest, Really I dont.

Since you know that induction is real, then you know this makes sense.

I'm a Factory Trained Land Rover Master tech, And I can tell you Spark noise, Bad Grounds, Etc are very real on all cars, and Rovers more so.

But! Since your smarter then I am, surely I am wrong. Thank gosh you pointed out that my fix is voodoo magic, as I have the car 30 feet from me and your 1000 miles away. I'm so glad I was proven wrong by someone who couldn't even tell me what colour the truck is. Sorry my bad.

I had a hunch, I confirmed it with a $2000 Snap On Pac Scope, provided no less by Land Rover, saw spikes coming from the alternator, tried a fix, and solved it.



Of course, I could point out it was a EE that designed it to run a power line under plug wires, but that would be mean.

 

[AlanB]

PM getting into a pissing match, nah can't be

Btw, I have a PhD in BS and I can't even change my spark plugs

 

[p m]

Chris, did someone spill his coffee on your pants?

 

[Surgeoh]

Chris, as my luck would have it, I have a master's in EE.

Hate to burst your bubble college boy, but all of your knowledge is based on theory. A tech's knowledge is based on real world experiece. I'd put my money on Chris. Besides, if the engineers in this world were perfect, we wouldn't need techs. If the man says it fixed the problem, IT FIXED THE PROBLEM.

 

[p m]

Do you know about induction/Spark noise?

I have a master's in EE.

Does it sound like a direct question and nearly direct answer to it?

all of your knowledge is based on theory

Where did I hear this before? Kyle, you have a competitor here!
Now, how about 16 years of building field equipment without a single failure sound?
And, by the way -

Now, take the formula and enter 50,000 volts going through the wire.

Does it not sound like theory to you? (that is beside the point that there was no formula in Chris' link to put any number in).

It is perfectly possible that the spark plugs induced significant voltage spikes in the 12V circuit. But, it is by no means normal - that means there is no capacitor inside the alternator, or it it is shot, or disconnected. Battery alone has enough capacitance to absorb the spikes induced by the spark plug wires - if it doesn't do it, there is a poor ground or 12V connection on whichever wire there is.

 

[Chris-St Louis]

This is out of hand.

Ok, Lets focus on the question.

Bottom line is it makes $5.00 to try my fix. It worked for me, it may work for you.

I have done it to other Rovers in the field, some with the same sucess, some with none.

Again, $5.00 in Bulk Stereo Wire, and a couple of crimp on ends.


I can say, the problem was much more pronounced after I converted from a Lucas to GM alternator.

On I got the truck, It was a worn out trade in. Compression was low, and it ran ok, no stumbles.

After I pulled it out to rebuild it, with 4.2 Pistons and crank and a Better cam, the thing ran great, but always had a surging idle. And, some hesitation and just simple weirdness.

I scoped the plugs and they were funky. I had the Distributor mounted modual, and a Extra MSD at home. Time for a update.

After I put that on, it got WORSE! (ARGH!), But liveable. I just lived with it.

Then, after going on a road trip where my Alternator died in Bloomington Ill, that was such a hassle I converted it to the Delco alternator. After that, It ran like SHIT! I mean, it would stall at idle, no power,just weirdness.

Scoped the alternator output, and found it jumping all over. 3 alternators later, the same readings each time.


The Battery was absorbing a bunch, but not all. Then I put a induction voltmetter on the alternator output, it was showing what the scope did. Big surges.

So, I tried a hunch, and it worked. Period, paragraph. And, Its either had no effect, or solved problems for everyone who I told.

I read everything I can on all the Rover Forums I can find. Also, I give some tips to the Rangerover.Net John. This is the first time I posted on here, because I thought I could help.


To have someone 1000 miles away tell me I'm wrong is just plain insulting, and will certainly not inspire people to want to help.

If you need to be the smartest guy whereever you go, great! Your smarter then me.

If you want to help people, your goign the wrong direction shooting people down.

Take advise for what it is.....A No Cost Idea.

I have some pics, if I can figure out how to upload them








Also, no coffee spilled on my lap.

 

[Chris-St Louis]

Picture of Nest the Power wire was run in.

Right under these plug wires is where the Brown Battery wire was run.

 

[Ian95rrc]

You can e-mail me the pic and I'll post it if you want. Just no pics of that ugly ass yellow plenum.

 

[Chris-St Louis]

I cant upload pictures.

http://www.rangerovers.net/rrupgrades/classic/engine/msd.html


Here is a link to my battery cable/MSD update. These are the pics I was going to upload.

 

[MarkP]

I have done it to other Rovers in the field, some with the same sucess, some with none.

I suspect Peter is correct in his observations and that Chris did fix his truck. I agree with Peter that Chris should not have observed large spikes on his alternator to battery connection. The battery is a large capacitor and under NORMAL conditions should absorb the spikes. Now Chris did fix his truck but his comment that this has fixed some but not all is the key piece of info. This means that something else is causing the spikes on some trucks, but not all. This feels like an electrical circuit that is high resistance and any induction current results in a voltage spke that disturbs other equipment. Eliminate the high resistance connectioin and the spikes go away. Or as Chris did move the cable away from the high voltage source to reduce coupling. It reduces the spikes but doesn't really find the root cause.

The problem is finding the marginal connection. I bet you find it down the road as some other problem.