'95 4.2 w/rough idle when warm...

[57loboy]

Esteemed colleagues, riddle me this:

'95 RRC LWB, 144k miles, complete top end rebuild 12 mos/7k miles ago, included plugs, cap, rotor, hoses, correct (non-platinum) plugs, etc with no drivability issues at all since. Suddenly starts running rough when warm, so much so that it stumbles at traffic lights and ultimately dies on my wife and kids while I am 250 miles away in parking lot. No SEL or CEL light on. Car will restart with no problem, only by massive feathering of throttle is AAA dude able to get it out of space for flatbed after 2 hour wait for him to show up.:banghead: Does same to put in garage.

I come home next day and discover the end of vac line to cruise diaphram is dry rotted and has fallen off so I snip end and replace. Car starts up perfectly, runs great so I take it for a ride. 6-7 miles later, when it is warmed up, starts to stumble when waiting at lights, roll into service station and it stalls out in front of the pumps. Restart and get into a space with very rough idle. No CEL or SES.

Have wife bring extra (new) stepper and some tools. Replace stepper, starts right up, then idles rough again. Local Rover enthusiast (thanks very much Paul!atriot: ) brings over known good MAF, stepper and ECU. Check for codes first - there are none. Replace stepper w/one of his - no change, no codes, no lights. Rough idle continues. Do same with MAF and ECU, no codes, no lights, rough idle continues.

It's home again in the garage (thanks to a trailer ride). I know in the AM if I go to drive it, all will be well until 6-7 miles of driving. Tank is full of 93 octane (well, the 1/2 I filled while at gas station at least, rest is probably 89). When running, the roughness smoothes out over 1500 or so, but the idles is real low and rough but never trips a code.

TPS? Other ideas? Help!

 

[noee]

Vss?

 

[Paul Grant]

Does the '95 have the VSS on the BW or if its the older style transducer that mounts along the side of the transmission?

If it's the same as what is on the Disco, I have one you can try Tom.

I also have a TPS with a round connector that is good. We can crimp on the square connector from the bad TPS I have at the shop to fit your truck and see if that is the problem also.

 

[sven]

Doubt its the VSS. My 1st test would b a fuel pressure test. See what it does when it happens.

There's also a fuel temp sensor on the fuel rail...used during warm starting. You can check the ohms vs temp chart in the RAVE to test it.

 

[MUSKYMAN]

coolent temp sensor I bet.

thinks its still cold so when it does get warm gets way to rich as it floods it stumbles and opening the throtlle plate leans it down and allows it to start and stumble.

let it sit it gets cold and the amount of fuel is then correct. so it runs ok again till warm.

try unplugging the sensor on the manifold and see what that does, it is right behind the thermostat cover it has a spring clip that connects it.

just a idea but easy enough to test for.

good luck

 

[57loboy]

Thanks guys - I'll give that a shot tomorrow evening. I got a handful of spare sensors from Paul this evening to cover all the bases.

It's just odd that it won't throw a code, guess it's within parameters not to trip it, but the car sure doesn't run well. And yes, the readout display does work as we got the correct 02 reading on the display when swapping the ECUs over.:ack:

 

[57loboy]

Update for all: Have swapped out all of the sensors with the exception of the VSS and the MAF and it's no different. I've even swapped plug wires and changed the fuel filter. I am getting a new fuel pressure tester/gauge tonight as the one I have doesn't adapt down for the LR style test valve. I'll report back with what I find - I suspect fuel now more than anything as it runs like crap from 1st startup now not just when warm. If I keep my foot on the accelerator, it'll run, but it will not idle - at all.:banghead:

 

[lforgue8]

I have a similar problem and i have tried everything except the dizzy basplate and checking fuel pressure when it dies.....i thought it might have been the relays from a thread awhile ago but my problem came up again.....

i too checked fuel and coolant sensors when running and when it wouldnt start and all were ok.....

my though since my fuel pump and wiring to it are new it may be the base plate in the dizzy getting hot and going open circuit!???

any way im going to try to check it out tonight and see......try this.....

when it wont start have some one crank it and chk the side of the coil for the pick-up and using a test light see if the light pulses. if it does then the pick-up is ok and its something else....

keep me posted

 

[57loboy]

Luc - since it's now doing it when cold, I really suspect fuel. i've got a new fuel test pressure setup and will be checking the fuel press tonight. Will post back with what I find - if all is well, I know I should see 35-38psi at the rail...(right?)

 

[lforgue8]

Luc - since it's now doing it when cold, I really suspect fuel. i've got a new fuel test pressure setup and will be checking the fuel press tonight. Will post back with what I find - if all is well, I know I should see 35-38psi at the rail...(right?)

yup that sounds right when you shut it off it should hold as well for about 20 min before dropping a considerable amount

didnt have time to look at mine last night maybe tonight :banghead:

 

[57loboy]

didnt have time to look at mine last night maybe tonight :banghead:

x2 :banghead: :banghead:

 

[lforgue8]

x2 :banghead: :banghead:

well i chekced my timing and idle speed and is ok stalled on me so i checked the pick-up and my test light pulsed....so i dont think its that so i checked power to fuel pump relay and its ok/ chk volt drop from relay to pump and had volt drop of 2.5v! i still dont think that would cause it to stall it stalls right away not like it runs out of fuel.

i may run a temp wire form relay to pump and see whats up.....i need to check pressure too!

im at a loss about this and its starting to piss me off cause im usually pretty good with this stuff:banghead:

i may also buy a new coolant temp sensor since its only about $20 cant hurt!

let me know how make out

 

[57loboy]

We've both been out in the garage tonight... Here's where I am at:

Fuel pressure comes right up to 38psi and holds beautifully above 35psi for 20-25 minutes. Did that test before I even cranked to see if it'd start. Now it won't start, it tries but won't catch. So, I checked for spark (the old bolt in plug wires against exh manifold trick) and we have spark. I cleaned coil connections just for giggles and we have 12v at coil. When cranking it tries to catch but doesn't, now I am really stumped...

Could it be the coil? Could it be the module? Could it be injectors as it won't even start now? It's obviously gotten worse since the weekend when Paul and I swapped plug wires after I swapped the fuel filter - it started from dead cold then, just idled like crap and then stalled out.Of course, still no codes are being set. Argh!

 

[ajtbussen]

Go throught the igintion electrical test in manual. If you go step by step you will find the problem if its electrical. I see bad dist. rotors give your simptoms. Good Luck.
A.J.

ps use only Lucas rotors

 

[57loboy]

It's got a Lucas rotor in it now with 7k miles on it.

 

[lforgue8]

It's got a Lucas rotor in it now with 7k miles on it.

X2

my coil, mod, cap, rotor, fuel pump, relays....etc are new less than 5k and im at wits ends man:banghead: :banghead:

 

[ptschram]

Brute force troubleshooting gentlemen! If it's not throwing a DTC, think back 30 years ago, what did we do when an engine wouldn't run right? We looked for mechanical problems, jumped timing, busted valve springs, blown head gaskets, etc.

 

[crown14]

Compression test?

 

[57loboy]

PT - thanks for the guidance earlier, I will be embarking upon the "brute force" diagnosing tonight... The more I think about, the way the car has gotten worse from all the attempts to start it, cranking and all, I think the timing belt and/or distributor may have crapped out. I'll report back once I have a diagnosis. Thanks again PT!

 

[lforgue8]

Brute force troubleshooting gentlemen! If it's not throwing a DTC, think back 30 years ago, what did we do when an engine wouldn't run right? We looked for mechanical problems, jumped timing, busted valve springs, blown head gaskets, etc.

my engine only has about 5k on it, compression is fine, timing is fine, idle speed is fine, coolant level hasnt moved in those 5k miles oil is clean the 3 changes ive made, mine is electrical some how i just dont know what yet..........now 57loboy's i dont know either it might be benificial to check the "brute force" things who knows!