jeepster11

I have been cleaning up my new 89...tune up, sea-foam, tightened my manifold bolts and idles great now. But it is hard to start, cold or warm, and I sometimes get a carbon exhaust smell. It always starts but seems to be getting worse. Could it be the O2 sensor and if so where is it located? thanks anybody

tampaviking

You should try primeing the fuel rail once or twice first. Turn the key till you here it click off. Then do it again, I doubt you should worry about the 02 sensor.

jeepster11

thanks...I read that here somewhere...I will try that tomorrow...

BlueXJ

BTW your 89 only has one O2 sensor and it is located on the downpipe just below the exhaust manifold flange.

jeepster11

thanks...I think you are the one that suggested changing the O2 if there was a potent exhaust smell and hard starting...thanks for the location...

91 Laredo

I was having similar symptoms after doing a tune-up, seafoam, etc.. It would run okay when it was running but was a biatch to start when it was cold. I removed the throttle body and cleaned it with a toothbrush and carb cleaner. I also removed the IACV valve and cleaned that too.

jeepster11

Thanks...tried the starting procedure but no luck....so today I cleaned the MAT sensor and the IAC....started a little easier. Next the throttle body and then check the TPS and maybe throw in a new fuel filter. The little bit of cleaning I did today seeemed to help so maybe your idea of throttle body cleaning is the answer.....thanks

zombie850

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5-90

Heh. RENIX.

There are two common causes for a "Hard Start" (I'm going to assume - I hate that word! - that you're referring to more of a "long crank" issue than the engine having a hard time lighting off...)

1) The fuel pressure check valve is failing, and the fuel rail is losing pressure and taking longer to develop it when you're starting. Check this by cycling the key OFF-RUN(pause)-OFF-RUN-START and seeing if the crank time shortens. There is a BMW part that can be plugged into the line that will work, but I don't recall what it is offhand. Searching <BMW fuel> at NAXJA would probably be instructive.

2) Look at the back of your engine. See that stupid little braided strap on the driver's side, connecting the cylinder head to the chassis? Believe it or not, that is the main ground for the chassis! It goes by some official name, but it's also known as "The RENIX Killer." If that ground gets faulty, then the ground reference for your ECU goes stupid and it takes longer to figure out what's going on - and it will recieve and transmit some spurious signals.

RENIX likes to see 300RPM at the CKP and a valid SYNC signal from the distributor before it will fire fuel injection and ignition. A failing ground can corrupt either of these signals - and they're both pretty weak. This is why my RENIX kits have the option of a secondary chassis ground directly from the battery - it usually helps. You can check to see if your chassis ground is going stupid on you with a set of jumper cables - connect one end of a single cable to the battery negative post, and the other to some clean metal on the chassis. Start as you normally do - if you've shortened your cranking time or otherwise improved your start, replace that stupid braided cable and add a secondary ground.

Please, do not ask me how I know all this! Although, Blue can probably give you a faster explanation of why I know than I can - I do tend to be a bit pedantic...

jeepster11

thanks for the reply..Question-if I try to release the pressure on the fuel line(using that pressure release gismo on the rail, when the engine is shut off) and there is no pressure....would that indicate the fuel pressure regulator is not working and if so wouldn't I just want to replace the regulator to attain the quicker starts...and keep the pressure up. And what is the advantage of the BMW valve over a new regulator. thanks

5-90

The regulator is not a check valve - it's just a pressure regulator. It's a "dead-head" regulator, which means it releases excess fuel pressure at the end of the line (which does control pressure through the whole system. RENIX just uses intake manifold absolute pressure as a trigger for the FPR - using a base of 1 atmosphere as "zero" and running fuel pressure some 39psi higher than whatever the MAP is, IIRC.) So, it's not the same part - the check valve, as I recall, is part of the fuel pump.

That "pressure release gizmo" on the rail is actually a pressure test valve, and if you have a fuel pressure test gage that fits GM-style fittings, you can use that to monitor pressure in the fuel rail. I don't recall how much pressure it's supposed to maintain, or for how long, but that can probably be found in the RENIX FI manual you can download from Pirate (consider it required reading. It's only 65-70pp. I'd get my copy, but I have carne asada going right now...)

I can tell you one thing tho - you should definitely see pressure retained immediately upon shutdown - if it drops right to zero, replace/augment the check valve. Using a gage is a much more accurate test than just pushing the pin in the Schrader valve to see what happens...

mycherokee1989

My starting is not the best, and I'm looking to see if any of your responses could maybe apply to me. I know which ground you are talking about, but with my jeep there is a ground running straight from the battery to the post where the oil dipstick connects to the block. (normal I'm pretty sure)
Why would this little ground (you mentioned) effect anything if there is already a ground going to the block? Or is the ground you mentioned taking the electricity from the engine off into the chasis?
Keep in mind I'm not an expert with electrical, or Jeeps really, so this may not make any sense.

ShortyzKustomz

I dont know about Renix but alot of 4.0 guys I know had long cranks and they all replaced the crank sensor and probs went away, Mine is a stubborn starter but its sat for a long time and need to sea foam and tune up before I figure my problem

jeepster11

thanks 5-90....I appreciate your sharing the knowledge. After reading your stuff and taking the jeep for a ride tonight and trying the shut off and start test, I feel it is slowly getting better...due to the seafoaming I did a couple of days ago. I have to keep telling myself the jeep is old and has seen alot of miles. I have enjoyed reading the chats here and tinkering on the jeep using what I have learned. I will keep the ground switch in mind and hook up a jumper cable in the next couple of days to see if the cranking becomes shorter. Again I think it is getting better as a result of cleaning the MAT, IAC and then seafoaming...thanks all

5-90

Because the ground I'm referring to is the primary ground for the chassis - which grounds by way of the engine block.

This is a problem because the entire ground plane (chassis sheetmetal and engine block) is used as the "zero reference" for various engine management signals. Thus, if the ground plane gets screwed up, signals get screwed up as well. This is why adding a secondary ground from the chassis directly to the battery is a good idea. You're reinforcing the "zero reference" used for the electronic controls, and that has the effect of making the signals to the ECU rather cleaner and easier for it to interpret.

Think of it as reading something written in black ink on a grey paper, vice reading it on white paper. The white paper is going to be easier to read - adding the extra chassis ground to the battery effectively "lightens the paper" to white instead of grey.